Laurent Tillon is head of biodiversity at France’s National Forestry Office, in charge of drawing up inventories of forest fauna, especially mammals and batrachians. He is the author of Listening to Nature (Payot, 2018), the bestselling Being An Oak (Actes Sud, 2021), and Night Phantoms: Bats and humans (Actes Sud, 2023). He lives in the heart of Rambouillet Forest.

Jessica Moore is an author and International Booker-longlisted literary translator. Her translations have also been nominated for the French–American Foundation Translation Prize, included on the New York Times bestseller list, and have won the UK’s Wellcome Prize and a PEN America Translation Fund Award.

She lives in Toronto, where she tends to her twins and her urban garden.

First published in the UK in 2025 by

ITHAKA PRESS

An imprint of Bonnier Books UK 5th Floor,

HYLO, 105 Bunhill Row, London, EC1Y 8LZ

Text and image copyright © Laurent Tillon, 2025

Translation copyright © Jessica Moore, 2025

All rights reserved.

No part of this publication may be reproduced, stored or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior written permission of the publisher.

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A CIP catalogue record for this book is available from the British Library.

Hardback ISBN: 978-1-80418-340-3

Trade paperback ISBN: 978-1-80418-342-7

eBook ISBN: 978-1-80418-339-7

Also available as an ebook and an audiobook

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I dedicate this book to all those who love trees.

To future generations, whose well-being – whose very survival – depends on the forests.

To Sarah, in whose name I have planted saplings.

May they grow together!

PREFACE

IN THE BARK OF A TREE

What are trees? We tend to exist alongside them without giving them much thought. And yet, they are essential to our very survival. Forests may be the lungs of the planet, but we often pass them by without truly paying attention. Most of the time, they are little more than a green backdrop.

It’s true that when you look at them, trees are fairly simple beings: no central nervous system, no vital organs, no heart or eyes, no ability to speak or move. Considered with a distracted – or indifferent – eye, it seems they must be incapable of feeling. But if we look closely, if we examine their reactions to the various challenges they face, we realise that plants show an extraordinary capacity for adaptation – one that’s almost impossible to comprehend with our animal gaze. To understand them, we must attempt to slip into the skin of the plant world – inside the bark of a tree.

Trees brim with life, from invisible roots to lofty crowns. Their seemingly simple internal organisation makes them, in many cases, more resilient than any animal. Their longevity is the clearest proof; a tree can live for several hundred years, and some species for more than a thousand.

* * *

I may be a biologist working on the forest ecosystem but it wasn’t until I leaned against the trunk of one, years ago, that I learned – in its entirety and integrity – what a tree really is.

Go to a forest or a park and stop to rest against a tree. If, like me, you’re lucky enough to feel a particular connection to one in particular, that’s the one you should sit beside. Otherwise, any tree will do, as long as you have the will to become truly interested in who they are. Place your hands on the earth, on their roots, and lift your head to look up at the canopy. Lose yourself in the rhythms of nature. Listen to the sound of the wind in the leaves. Close your eyes for a moment, then open them again and look at the tree. Examine each of the shapes they are composed of. You like the tree because of the way they are. Their shape is the reflection of their lived history, and of their environment, both of which have gradually sculpted the tree to become who they are.

Who and what are trees? This book will give a long answer to this seemingly simple question. They haven’t always been big, tall, monumental. We have to go back in time.

Let us turn now to the main character of this story, a being whose life impacts the environment as much as it is shaped by it: an oak named Quercus.

INTRODUCTION

MEETING MY TREE COMPANION

On Earth, there are three thousand billion of them – almost four hundred and twenty times more than there are humans. They are vital for life to carry on. We depend on them, not least because they produce the oxygen we breathe. And they are everywhere: trees have colonised almost every environment, even deserts, proving they are capable of extraordinary adaptation. In recent years, research has revealed many of their secrets. But what, or who, are they really? And why do we feel such a compelling need to get closer?

There is a very ordinary oak at the end of the road where I live, near the entrance to a forest. Actually, it’s not quite that ordinary: it is my tree. I enjoy visiting it every so often, and I have noticed that this particular oak has the power to relax and calm me. It has a reassuring nature. Whenever I walk towards it, I feel an inexplicable sensation of happiness. If I had to sum up its role, I would describe it as something like a companion. I have become convinced that every one of us should have a companion tree to help us unwind.

Have you ever felt this kind of almost visceral attraction to a particular place? Somewhere you like to spend time, where you are completely in the moment? Where you feel at home? I’d be willing to bet there is a tree there. Maybe it’s your tree, a tree that one day ‘called’ you. And maybe you went in spite of yourself.

I first felt this call as a teenager. It happened slowly, over months and years. Without being fully aware of it, I grew deeply attached to this little corner of the forest. Some parents give their children one: a tree that’s planted when they are born. They will grow together and share all the events of their lives.

This animal–vegetable bond may seem a little one-sided, but I believe the trees we love may not be oblivious to our presence. I find this quite comforting. Whereas biologists usually only trust what they can prove with a rigorous, experimental, scientific approach, here I’m following my intuition. I have the distinct impression that I’m communicating with this oak every time I visit it.

How could I suggest that a plant has even the slightest hint of intentionality? I can’t answer that question, but perhaps the easiest way to understand is to think of it as having not so much a technical ‘consciousness’ as a kind of ‘personality’.

And already, I’ve fallen well and truly into anthropocentrism, which was something I wanted to avoid. The truth is that a tree might be far more than just a simple plant, and yet we cannot describe it in animal terms without some inaccuracy creeping in. Ultimately, attributing human emotions and feelings to it would be doing it a disservice. It is so much more than that.

* * *

My oak, Quercus, is two hundred and forty years old. While fully mature, he has not yet reached the middle of his life. When I observe his neighbours, I can, of course, see differences. He is the tallest in his pack; the first branches bearing leaves are at the top of his crown, while others lower down are dead. His south-facing foliage is particularly well developed, whereas none of his boughs grow towards the north. On one side, there is a large open space beneath his crown; on the other, a beech has taken up as much room as it can, its branches reaching almost to the ground. Strange, then, that this oak has not taken advantage of the empty space there to grow a branch rich in foliage, isn’t it? All trees respect a boundary, leaving a non-invasive space a few centimetres wide to avoid damaging each other, and leaving the sky visible between their leaves. There is a hole in the fork between two of his branches: a home drilled by a bird that made its well-sheltered nest there. I wonder: did our tree suffer as a result?

Some of our oak’s neighbours are trying to catch up with his height to win more territory, while others are overpowered and have had to give up their access to light, such an essential resource for their growth. There are large beeches with abundant foliage, several of which have trunks riddled with holes much larger than the one in my oak, dug out by the largest member of the woodpecker family, the black woodpecker. There are birches and Scots pines – scars of the successive wars that have marked our territory. In the undergrowth, hornbeams, holly and smaller beeches all await their turn, and keep the more vigorous trees company.

Further on, an oak, a cousin of my tree companion, stands dead, rigid and desiccated. Among the fronds of neighbouring trees, its leaflessness permits a shaft of light to reach the ground. Lush, flower-filled vegetation has reaped the benefit and found a way to express itself at its foot. There are purple-blooming foxgloves there, alongside a bramble bush that is over a metre high but fending off the still-larger ferns that surround it. A stump lies on its side: a sign of a storm that upset the forest’s equilibrium. Another, still in place, testifies to our age-old exploitation of wood. A few hairs on it reveal the presence of wild boars, who have scratched against the bark to remove parasites hidden in their coats.

Bracken has taken advantage of long-ago fires lit by humans to make advances in the undergrowth, its density preventing young trees from growing. My tree is surrounded by compact soil made from dead leaves, but a little further along I see two species of heather, vestiges of an open forest landscape that was once more like a wooded heath than the forest as we know it today.

Further still, birches, the quintessential trees of our Northern European forests, benefit from a marshy area. They are followed closely by a few colonising Scots pines. If I look carefully, I can pick out a succession of ditches and embankments, revealing a past use of this space by humans, though it is difficult to pinpoint exactly what they used it for.

* * *

What is a tree? The clues are multiplying, and we can already provide some answers. This landscape helps us begin our investigation. One side of the forest probably grew on former heathland. The other might result from woodlands where large oaks and smaller trees were coppiced – in other words, regularly cut back by people living nearby, probably for firewood. My tree reigns in the middle, this magnificent oak, the species sometimes known as the ‘king of the forest’ – his presence supports a plethora of animal and plant species, which would otherwise have no chance of survival.

The oak is home to more animal and plant species than any other tree, as well as hosting microorganisms. His death would lead to a dramatic change in this forest’s biodiversity. All in all, the interactions between this ‘tree being’ and his environment are numerous and complex. Humankind is just one of many species playing a part in this story.

Thirty metres away lies a sandy path, where countless animals, travellers, king’s couriers, foresters, lumber-jacks, coal miners, and hunters and gatherers have passed, and, more recently, cyclists and walkers. Among them was once a kid from the Eure valley who rode through the Rambouillet forest. He was a teenager trying to find himself while Quercus was just emerging from his own adolescence at the venerable age of two hundred. This kid – me – was overcome by the beauty of the place each time he rode along the sandy path and looked up at the tall trees. One time, my chain came off, right at the foot of the oak – it was as though something was compelling me to stop in precisely that spot. I was fifteen. I lifted my head. There he was, majestic. This tree. A sessile oak, whose scientific name is Quercus petraea. His genus name, Quercus, comes from the Celtic kaer, meaning ‘beautiful’, and quez, which means ‘tree’. Petraea comes from the Latin and means ‘rocky’. Quercus: the beautiful tree, solid as a rock.

* * *

I didn’t know it yet, but in that moment, a calling was born. Quercus was the involuntary witness (at least, I don’t think he played an active role). The scientist I have become doesn’t dare believe a tree could have actively contributed to this growing awareness within me. Impossible – isn’t it?

* * *

Ever since that day, I’ve come back to visit my sessile oak, and his effect on me remains the same. True joy. I have lived near him all these years. By examining the architecture of his branches, I can partially reconstitute the events that led him to the present day. When I observe the surrounding environment, I can read his history, which is far from being over – I am but one passage in Quercus’s long life. Centuries of adventures still await him. But Quercus reveals his story to me, in a simplified exchange, through the events he has lived through, and the encounters he has had with other species that have given him the form I know today. He tells me he hasn’t always remained fixed in that spot, enduring the ravages of time.

We talk about the global changes that affect the climate. Quercus has been sensing these changes for over two centuries. And the forest of today is very different from the one Quercus was born into. He has seen the landscape transformed by human beings, but not only by us.

For those who know how to listen, Quercus becomes an inexhaustible chatterbox. An exchange, if you like, between plant – this oak – and animal – a human being. It may seem difficult to believe that such an exchange is really possible. And yet, the tree shares his story with me. Not only does he share, he also urges me, at a time when our environment is threatened by so many crises, to tell his story to as many people as possible, and to explain that the forest and the life of trees are made up of stirring adventures, with many twists and turns, over the centuries. Quercus wants me to urgently convey that we need to take care of trees. As though to remind us that in these troubled times, the forest can provide the opportunity for a return to simple values, closer to our individual needs. And that human beings should remind ourselves now and then of our animal origins.

In Quercus’s story, we begin with a savings plan gone awry, but whose investment wasn’t completely without a return. Next, a seed, which, taking root, would give rise to a shoot pushing against gravity towards the light, defying the laws of nature to take its place among its own kind. Then, attempts on the part of several animals to take advantage of the resources Quercus knows how to access and transform.

There will be parasites and herbivores who attack its foliage. There will be invaluable allies. Encounters, some incidental, others intentional – some that began as attacks but turned out to be life-saving and symbiotic. There will also be betrayals, mutual assistance and competition, because making a place for oneself in the forest is not easy, and the number of competitors at the starting line is considerable. Then will come the joining of Quercus’s history with that of one particular species, humans, who shape the landscape as much as they profit from the natural resources provided by trees. Finally, an intertwining of relations between very different species, and this will create a kind of balance between all of them, for the benefit of not only a few, but the whole community – all these representatives of life! This beautiful demonstration of true communal life and solidarity may inspire some readers. And through all this, we’ll discover how Quercus was able to make it through, even though things seemed so precarious at the start.

* * *

Quercus tells me that his life began with a journey.

At the beginning of this long story, there was a seemingly terrible fall, but one essential to his true beginning.

Once upon a time, there was …

QUERCUS, THE OAK, 1780

In which we learn that Quercus, small as he may be, is brimming with energy, which can sometimes get him into trouble. That while he is still attached to his mother, he is already in grave danger; but that abundance will be his saving grace. That he will have to go on an adventure and gain his independence.

The year is 1780.

… An acorn!

The hope of a centuries-long future awaits.

* * *

The history of ‘my’ Quercus begins more than two hundred and forty years ago, at the top of an adult oak that has since died.

At that time, just before the French Revolution, the surrounding countryside resembles an enormous heath, with woodland at one end, populated by tall, scattered trees and a few clumps of coppice. A marsh signals the out-crop of the water table. People come to take advantage of nature’s resources: strands of heather to make brooms, and forageable morsels, such as mushrooms, chestnuts, acorns, hazelnuts and blackberries. But the trees are sparse, and the woodland looks more like a bright, airy space than a dense forest. The tall oaks are a resource for humans, providing wood and nuts in particular, and offering animals shelter during the hot days of summer. This forest is radically different from the one we know today.

For several centuries already, humans have had dedicated spaces for cultivating wood. The tall oaks have one main purpose: to serve the will of King Louis XVI, whose grandfather had considerable maritime ambitions of trade and conquest, which required a prodigious quantity of wood. He was also the man who, in 1669, began to organise forest management with the help of his controller general of finance, Minister Colbert. To build the essential boats, each curve of a tree will be used for particular parts: hewn beams, forecastle or poop deck beams, floorboards, futtocks and curved stempost or sternpost beams. Other trees, cut every ten to twenty years, sprout new shoots from their stumps that will be cut again as fuel for heat and cooking. Finally, some oaks will be dedicated to the construction of dwellings on the outskirts of the forest. The rhythms of life, here, are well-tuned to those of nature. One species in particular – humans – benefits from this, and has shaped the landscape to get the most out of it for centuries.

* * *

These are the circumstances into which Quercus is born. It would be difficult today to identify his parents – they have most likely died. The sessile oak is a monoecious forest species, which has as many male flowers (catkins) as female ones. The precious grains of pollen from the male flowers are so light that the winds of May carry them easily towards female flowers. Thus, the ‘father’ can be the same tree as the ‘mother’ through self-pollination – a rare phenomenon in oaks – or the father can live some distance away in the forest stand (cross-pollination). Once pollination occurs, the acorns form in groups of two or three. These clusters have a very short peduncle – a stem attaching them to the branch. The hat-shaped cup protects them and keeps them joined to their parent tree until they mature. Four months later, the essential elements for the transport of genetic heritage adapted to the conditions of local life are ready. The parent tree has provided organs to ensure development: inside the acorn, a plantlet and a radicle are ready to germinate, protected by two cotyledons loaded with starch, the fuel required for germination. The external pericarp and internal integument make up the protective envelope. Because it’s always good to have more than one string to your bow, the parent tree bequeaths a good dose of tannins to make the acorn less digestible, discouraging those who might try to eat it. The main player, sporopollenin (a mix of fatty acids and complex molecules), strengthens the protection of seeds and grains of pollen. Quercus is particularly rich in this. He has enough food reserves and multi-faceted barriers to give him every possible chance of survival: the acorn is ready.

* * *

But already, Quercus’s life is at risk. A few acorns on a neighbouring branch have attracted the attention of female weevils of the Curculio genus. These insects use their rostrum to make a sort of drill that spins from left to right, piercing the tegument and pericarp. It’s a long, fastidious job, so demanding that they must regularly stop to rest. But, in the end, the weevil always manages to break through. It then turns around, inserts the pointed ovipositor at the end of its abdomen, and places an egg in the centre of the acorn, inside one of the two cotyledons. The larva, unaffected by toxic tannins, can then take advantage of the starchy resources to develop and give rise to a new generation of weevils, extracting from the acorn all its vital promise.

* * *

Quercus is probably blissfully unaware of this threat while still attached to his birth branch. Nevertheless, while only two centimetres long, still in the lap of its parent tree, he is already fighting for his life.

Nearly five hundred kilograms of acorns finally reach maturity in September, all at the same time. Thousands of ‘sisters-brothers’, all waiting to leave the original oak. Only a few will survive to adulthood; in the end, the vast quantity of acorns produced, and ultimately lost, are what protect our Quercus.

His peduncle has held him to the tree and now Quercus has reached maturity. One day, seasonal stimuli – such as a decrease in daily sunlight – inform the parent tree that the time has come for its offspring to let go and explore new spaces. All that’s needed is a gust of wind, the smallest impact, or an insect landing nearby for the acorn to let go and fall to the ground. Jettisoned into the unknown.

And this is exactly how, after a fall of several metres, Quercus lands abruptly on a soft bed of decomposing leaves. Impervious to the shock, Quercus has only one option now, one single destiny: to germinate and take root.

APODEMUS, THE WOOD MOUSE, 1780

In which it becomes clear that Quercus is confronted with multiple risks, and that one of his worst enemies will become his closest ally; that once again, the multitude of sisters-brothers is the gauge of survival, and that, despite appearances, Quercus has unwittingly been travelling since infancy.

The year is still 1780.

Although it’s the middle of the day, Apodemus the wood mouse can’t stay put. He waits at the entrance to his burrow. In his short life as a rodent, Apodemus has never seen so much food – a veritable treasure trove that has fallen from the sky. More than a hundred acorns per square metre! Soon the ground will be completely covered. The abundance causes more than one creature to salivate. How should the mouse approach the situation? His quest began as soon as the first acorns started to fall. Grabbing one, carrying it to a hiding spot, gobbling it down as quickly as possible, and running back for more. There were so few acorns last year, and now, there are so many the mouse doesn’t know what to do, taking a bite here, a bite there, he’s thrown into a frenzy, a bulimic desire to devour them all. Not knowing which way to turn, Apodemus moves from one to the next, leaving behind a trail of carnage; those partially-consumed acorns have lost all hope of one day germinating. A hecatomb for oaks. Terrified he won’t have enough, Apodemus begins to gather them up to stash away for later. He carries them to his hiding places, some as far as twenty metres away from his burrow. Saving is not only the domain of the squirrel: every self-respecting rodent puts resources away, in the hopes of a peaceful winter.

* * *

Quercus, weighing around three grams, is a reservoir of starch, which provides him with enough energy to make the first roots, the first stem and the first leaves. But while these reserves are very nutritious for Quercus, they also rouse the appetite of several animals. One is the wood mouse, and its diet relies in large part on this nutrient resource. In the years that follow abundant acorn harvests, the population of this twenty-gram mouse, Apodemus sylvaticus, multiplies rampantly, sometimes reaching a density of up to thirty, forty, or – in very rare cases – more than fifty rodents per hectare. But this doesn’t generally last. Higher numbers of the little mammals have a dramatic consequence for the offspring of the parent tree: every year, they all get eaten. Because oaks don’t produce acorns annually, the number of wood mice fluctuates from one year to the next. When their numbers are high in the year following a good harvest, the oaks don’t produce any acorns, resulting in a population crash among the rodents. After several lean years, another good one will follow, when there are very few mice around to eat the precious seeds. The oaks take advantage to reproduce en masse, outwitting the mice. The plant world fools the animal. We call this phenomenon ‘masting’. According to forest species, the duration between two productive years can range from two to four years. For oaks, temperatures in April must be above eleven degrees, and must also be higher than the previous April. Since conditions differ from one year to the next, the reproduction of oaks alternates. This plant species is well versed in this cyclical phenomenon and produces its seeds on average every three years.

As we might expect, the number of wood mice is low this autumn, in keeping with the natural cycle. Temperature conditions were met, and the oaks responded collectively to this climatic stimulus. They spawned massively, so the high number of acorns would ensure at least a few would make it through to germination. Apodemus, our compulsive collector, must go to great lengths to take full advantage of this new manna.

Quercus is not the only acorn to have fallen from the parent tree. There are thousands whose function, like Quercus, is to ensure the survival and continuity of the species. Time is of the essence for them all, but the ones that have landed on soil with no vegetation are particularly vulnerable – a few dead leaves not being enough to conceal them. Aside from the gift bequeathed by their parent tree, their solid cuticle rich in tannins, they have no way of defending themselves against aggressors.

And so, the autumnal fall of Quercus and his sisters-brothers is followed by the near-immediate arrival of acorn hunters – so many, that the chances of Quercus making it are almost zero. Caterpillars of seed-eating butterflies, gall gnats and acorn weevils have attacked several of his sisters-brothers, either to eat them or to lay their eggs. In the last case, their larvae will grow inside the shelter of the precious cuticle and eat the starch. Although the acorns appear to be intact, small holes visible in their outer shells reveal the quick exit of insects that in just a few weeks have completed their growth cycle. Apodemus must work quickly to select the intact, edible acorns and tuck them away.

While the insects are still here and continuing to arrive, there remains a greater danger for Apodemus and Quercus. Throughout the Ancien Régime, lords would allow their serfs to gather acorns, or graze their livestock in the forest so they might fatten up before the winter. Pigs in particular love acorns, and their ultraefficient digestive system allows them to minimize the toxicity of the slightly astringent tannins adult oaks have bequeathed to their offspring. (During periods of famine, people ground acorns for flour and used it to make a barely edible ‘acorn bread’, or ‘oak bread’, which had to be cooked for a long time and chewed even longer to render it digestible.) And indeed, today, there are pigs passing by a few metres from Quercus. From his tunnel protected by the trunk of the parent tree, Apodemus is well aware of the exceptional opportunity to make stores for the winter but wonders if he should take the risk. He hesitates, pokes his muzzle out of the tunnel. His whiskers, sense of smell and acute vision alert him to the dangers outside his burrow, as well as sources of food. The situation is unbearable. The large mammals are only a few metres away, but the scent of the acorns is too strong to resist. He launches himself from his shelter into the open.

* * *

Pigs don’t just glean berries and seeds – they will occasionally eat small animals that have the misfortune of being in their path. Danger can also come from the sky – a bird of prey, for example. Apodemus takes hold of Quercus by planting his incisors into the cupule, and then runs the twenty or so metres that separate his tunnel from his personal stash in a bramble. To do all this, Apodemus must pass between the feet of the pigs. One notices him, but our rodent is exceptionally lithe. His cousins, voles, prefer to move beneath leaf cover or through tunnels they’ve dug in the ground – this way they’re protected and able to move inconspicuously. The wood mouse adopts an inverse strategy – he bets everything on his speed and his weaving paths. In French, farmers even call the wood mouse ‘ça file’, or ‘there it goes!’ The fast one! This is why Apodemus can afford to take his chances. The pig gets excited and tries to catch him, but in vain – the mouse escapes. The pig soon forgets him and turns back to the acorns, just lying there for the taking.

Many trees produce very light seeds, such as maple tree keys, which are sometimes carried several kilometres by the wind. We call these ‘anemochores’. Acorns are heavy and fall straight down. At most, they may become scattered over a few hundred metres by land animals, to be used as winter stores, or sometimes up to ten kilometres by birds, corvids in particular, such as the Eurasian jay, the magpie or the black crow. The parent tree’s landscape is, for the moment, a heathland with only a few trees, as well as some heather and a few blackberry bushes taking advantage of the open space. The forest is thin, the heath exploited by humans, and the repeated passage of large animals decimates the vegetation. Here, on the dead leaves where he fell, Quercus was condemned to remain in view of anyone passing, and probably to be parasitised or devoured in a few days. Without realising, Apodemus has done him a huge favour. Now that he’s protected by thick and prickly bramble vines, there’s no risk of being found. Unless, of course, the rodent returns to eat him. But Apodemus doesn’t return. Like other rodents, he can forget the location of some of his winter stashes. So, Quercus is safe, under an unexpected shelter, one plant protecting another.

In the end, the oaks’ reproduction strategy has worked, and a few among the thousands of acorns escape their hunters. Some acorns have been stashed in this bramble. There is a future for these survivors.

If, that is, they germinate.

QUERCUS, 1781

In which we discover that Quercus has been confronted with a particularly harsh winter, but has survived. In which we learn that the protective bramble has allowed him to anchor and develop roots, a stem and leaves. There is the promise of a bright future.

The year is 1781.

Quercus is hidden beneath the impenetrable bramble. Other acorns, too, have resisted all the parasites and granivores that hoped to take advantage of this rich nutritional resource. But in the end, only a few make it to winter.

The first frosts grip the wooded heathland, and Quercus goes dormant, just like the other seeds, whatever their species.

* * *

Let’s hope the frosts are neither numerous nor severe. The tissues of the seed would freeze and the plantlet and radicle could be damaged. Still, dormancy has a protective and life-saving virtue for the fruit of the forest tree. The genetic heritage included in just a few plant cells remains safeguarded in the heart of the acorn.

* * *

One after another, the winter nights are harsh and bitter. This period is particularly disastrous and the plants and neighbouring populations pay the price. These winters will count among the most terrible, and agricultural yields will be impacted. People will go hungry; some will die for lack of food.

The short days offer few opportunities for growth. The forest lies in a deep sleep. Quercus loses his hat, the cup, but his reserves and his cuticle protect his vital force, and maybe the bramble helps a little as well.

Conditions are harsh; snow, rain and wind mark the days.

The winter passes in this way. Time doesn’t matter to Quercus. He waits for the awakening of spring.

For him, it’s as though time has stopped.

* * *

During the winter, a few more acorns are lost. A band of wild boars chomp up the few still out in the open. These animals are rare. Wild game were hunted relentlessly, to near-extinction, by nobility in need of adventure. Quercus was born in a royal forest where deer are the preferred prey. Lucky for him, although the boars’ fur and thick skin would protect them from bramble, the pack avoids it and moves on.

* * *

Even if late frosts continue, rising temperatures and longer days announce the return of the growing season. For the seeds that have made it through their first winter, the time has come to germinate. Winter rains have bathed the underbrush in a permanent humidity that envelops each seed.

Quercus drinks it up.

And in just a few days, the acorn’s envelope fissures beneath the pressure of the plantlet and radicle. These two organs quickly detect which direction to take. The radicle is Quercus’s first root – the one that will allow him to anchor in the nourishing earth. The cells at the tip of this root are loaded with starch, which makes them heavier than the others. Gravity pulls them down in spite of themselves. The tropism of the radicle pulls it towards the ground to give birth to the first axial root. It moves around a few obstacles – a decomposing leaf, a twig – to reach the sandy loam soil. It begins to plunge in and seek the support of nutrient resources. When necessary, it’s helped by mucigel, a lubricant it produces that allows it to slide past any obstacles. Plants don’t speak, apparently; but on the scale of our axial root, this movement makes one hell of a racket. Not only do its cells push aside molecules and nourishing earth, they also split on all sides to make room for new cells that gradually make up this new organ. In spite of its prowess, the root has a fairly difficult time finding enough water and mineral elements to help in its ponderous growth. It quickly exhausts the supply of starch in its two cotyledons. The axial root can’t do this alone: it has too many missions to accomplish. It must find water, trace elements and maximum nutritional resources. Each may be found in different parts of the soil, but how to gather them all without getting lost? And how to avoid the competing needs of the few sisters-brothers who also made it? The fact is, they all want access to the same resources and there’s no guarantee there will be enough for all of them. And now that Quercus is rooted, he can’t move at all and must make do with what nature offers. This will be his calling for his whole life, where he will have to adapt to local resources and the presence of his neighbours, themselves hungry for the same nutrients, or die. Becoming a multiple being is the only solution. His first root begins to divide, forming the beginning of a complex root system that will feed Quercus for the rest of his life.

Now that several roots are developing around the central axis, the taproot, they can strike out in search of the various resources necessary for Quercus’s development. The tip of each one, its apex, is a veritable homing device. Nothing happens by chance. The apex detects vibrations emitted by the growth of neighbouring roots and takes its place in the underground environment without encroaching on the terrain of its counterparts. Each one has its place. All the elements are essential to Quercus’s survival and growth: water, of course, but also trace elements and macronutrients – phosphorous and nitrogen in particular – oxygen (yes, the few rootlets that touch the surface catch some of these molecules, so vital for animals) and carbon dioxide. The tip of each rootlet makes a choice that does not depend on an order given by Quercus directly but that responds – without us knowing, still, which mechanisms are involved – to a collective reaction to different needs expressed by the complex individual Quercus is becoming. One root plunges towards water while another goes to find pockets of trace elements scattered laterally. What counts is respecting the space of each prospecting neighbouring root so as to raise the collective chances for Quercus to get everything he needs for growth. According to the stimuli received, the apex will head downwards, laterally or upwards. In this way, the root organ plays multiple essential roles for the tree: it constitutes a permanent nerve control centre, managing an enormous amount of information, such as weight, humidity, light, temperature, atmospheric pressure, sound vibrations, the presence of minerals and other nutrients or toxic elements to be avoided at all costs. And if a piece of information needs to be transmitted, several solutions are available: the use of chemistry, by transmitting the molecule found in the soil to Quercus, or by emitting an electrical field that spreads the message, the content of which, although still a secret to scientists, seems to provide precious information to neighbouring roots, which are capable of interpreting it. We’ll come back to this.

The root system, although still only a few centimetres long, establishes itself. Bit by bit, Quercus acquires the organs that are still mostly a mystery to us because they’re invisible beneath the ground, but we do know their role is complex and their function is vital. The two cotyledons have separated, in particular to supply the first root with energy. With the little energy they have left, they must also feed the plantlet. While the radicle only had to dive into the soil, the plantlet forms a stem that, in contrast, must rise up, towards the sky in order to reach the light. Quercus must defy gravity. This will be the very essence of him when he grows: diving, on the one hand, into the soil, and on the other, rising towards the sky. Shaping himself in contradiction to this one law of nature, Quercus must reach the heights, while remaining anchored in the soil.

When Quercus is just a few centimetres tall, the plantlet gives the last of its energy to make his very first leaves emerge. Five or six, that’s all. Even though shade is significant under the protective plant, he tastes his first photons, those particles of solar energy he needs to survive. Is Quercus capable of feeling emotions? Does he feel joy in the fact that the cells on the surface of his leaves can drink in this vital energy? Is there some form of exaltation, of happiness, for this burst of life that fills him with new strength? No one knows. Either way, his very future depends on this light. And there’s lots of it in that first spring.

* * *

Quercus still faces a challenge – the stems and leaves of the bramble form dense cover. Like every self-respecting oak, he needs direct light, needs to feel the sun’s rays warming each cell of his leaves. But the grey shadow of the bramble sucks up most of the sun’s energy. If this continues, Quercus is at risk of stagnating. Could this be a blessing in disguise, though, for the time being?

Spring heralds the herbivores coming to eat the tender leaves and enjoy the accessible buds. A deer passes close by the bramble. A few acorns had escaped the pigs, the parasitic insects, the woodland mouse, and then the wild boars. But this deer destroys all their arboreal hope – it munches the stems and leaves of the young oaks that have remained in full light. Some will still survive, but will never grow tall enough to escape the teeth of ungulate herbivores. They’re subjected to a life somewhat like that of bonsais, having to make new above-ground growth in an attempt to reach photons with new lateral branches, until, in the shadow of other bushes and trees that have managed to grow taller, lack of light condemns them to abandoning the game.

* * *

Although being caught inside it means Quercus must struggle to reach the sun’s direct rays, the bramble turns out to be a life saver; it prevents the deer from getting too close. Both protectors and tormentors, brambles are sometimes essential nurseries for baby oaks.

LECCINUM, THE BOLETUS, 1782

In which we discover that the soil holds a number of surprises for Quercus, and that he will encounter organisms very different from himself: fungi. This encounter will be violent, and Quercus will be betrayed. But this symbiosis will provide him with new vital energy. He will subsequently gain access to an extraordinary world of exchanges that transcend the barriers between species.

The year is 1782.

Sitting at the foot of Quercus, I observe a dead oak in the clearing a little further along. A small bramble takes advantage of the opening and the light coming through the tree canopy. It sometimes produces a few berries that I like to pick, juicy if the summer has had some rain. What a treat! While I graze on the fruit, I notice the stems of young oaks trying to reach through this impenetrable bush. Their destiny seems very precarious to me. But their challenges might also be a boon for other forest organisms. And perhaps they will get some help from another species, allowing them to eventually escape this thicket.

Given his environment and the history of this forest, which we’ll come back to, it’s likely that Quercus was subject to the same constraints at a very early age. Receiving help from others would have been vital for him.

Let’s go back to his first summer as a young plant.

* * *

Quercus is floundering. He benefits from a few photons that penetrate the bramble, but he needs more space. The bramble is stifling his development. If this situation persists, he’ll end up withering in spite of all his efforts.

During this time, Leccinum spreads out and develops her network as much as possible. Because she’s infinitely tiny, she goes where she wants and reaches a multitude of mineral resources hidden in the ground, such as water, which can be rare.

Leccinum is a fungus, most recognisable to humans when she fruits. The orange oak bolete is a favourite of connoisseurs. But most of the time, Leccinum quercinum hides in the ground and stretches each of her filaments as far as possible. Each year, in this way, she extends nearly thirty centimetres. This might seem ridiculously slow, but for an organism moving through the soil, and for whom the diameter of its tissues is around five to ten micrometres, this progress is a feat.

Leccinum sometimes fruits by making an epigeous mushroom; it emerges from the ground with a cap covered in thousands of spores, or tiny seeds, promising dispersal and perpetuation of the species. But most of the time, Leccinum is invisible and leads a subterranean life. She is made up of hyphae, very fine filaments capable of stretching out into the volumes of earth and humus of the forest floor to compose a dense network called mycelium. This allows her to exploit large volumes of soil to reach basic nutrients such as nitrogen, potassium, phosphorus and magnesium, and trace elements like copper and zinc. But gathering these chemical elements is one thing – preventing their recrystallisation while they’re being transported through the very narrow hyphae is another. For this, she produces citrate or oxalate, organic acids that can break up complex molecules so they can pass through the tubes more easily.

The mycelium becomes an enormous circuit through which molecules circulate in all directions, without ever being stopped, except to create new hyphae. But, like all fungi, the bolete has one weakness: she can’t make the sugars, lipids, vitamins and complex molecules necessary for her development. She can survive for a long time on simplified molecules from the ground, but then she’s condemned to stagnate, and will never be able to fruit, reproduce or scatter her spores to conquer new spaces. In order to flourish, she must find resources elsewhere. She must ask for help and form alliances.

Long ago, in her search for partners, Leccinum found a tree. The connection of her hyphae with the roots of an oak allowed her to absorb these essential nutrients in exchange for water, trace elements and mineral salts. The pact benefits them both. But the oak has aged, and keeping all her eggs in one basket is too risky for our fungus. It’s in Leccinum’s nature to multiply her partners, without abandoning the already-established partnership. When you’re mycelium, you play every angle.

Leccinum is slowly expanding her network and continuing her search when she detects some very particular structures emitting a signal that leaves no room for doubt. She has come across a very young oak who has just extended a brand new root into the soil. If she heads directly for this root, the oak will probably react badly. He might not be able to prevent contact, but the connection would immediately be considered an act of aggression. To facilitate the encounter, Leccinum seeks the assistance of a structure whose activity could be considered diplomatic, the rhizobium, to mediate. When it extends into the soil, Quercus’s root emits molecules that can resemble hormones – flavonoids or betaines which help it to better resist stress related to heat or lack of water. Quercus naturally produces the hormones to protect his root system. But his emission has an indirect effect: bacteria that also need water detect them, move toward them in the soil, and agglomerate to form nodules, like tiny little balls that make up the beginnings of the rhizobium, right before the apex of the emitting root. They are also naturally nitrogen-fixing, which the plant can benefit from.

These unique structures are mainly formed during the development of the root system of leguminous plants, such as peas; for oaks, there’s still some doubt about their existence, but it’s likely. So Quercus would benefit from these bacteria coming closer. The nodules they form aren’t part of our young oak, and they demonstrate its capacity to accept partnerships with outside organisms from a very young age. So why not Leccinum? The latter perceives a chance to make contact with the growing tree, taking advantage of bacterial diplomacy.

Aside from soluble mineral ions and surface water, Quercus is unable to find all the nutrients necessary for his development. The tissues that form the extremity of his roots open to absorb the nitrogen agglomerated by the rhizobium bacteria. By opening in this way, the roots are prepared, in spite of themselves, for a new encounter. This is how Leccinum’s hypha enters the newly established relationship. The bacteria detect the opportunity to reach the coveted water, and then the door opens. The hypha goes straight to the heart of the root’s epidermic cells to begin the partnership, limiting the oak’s defensive responses; without this, the oak would feel attacked. Indeed, Quercus makes a simple acid, jasmonic acid, which helps warn neighbouring cells in case of attack. He uses it in his leaves as much as in his roots. The acid is corrosive, so it is avoided by intruders. But in reaction to these protective molecules, Leccinum makes neutralising proteins. The strategy works and Quercus is invaded, despite his defences.

First he was betrayed by bacteria, now by his own organism. But strangely, this breach in the defences of the young plant will cause an inverse effect when he’s grown: much later, the tree will react fiercely to each attack and make molecules that allow for a more efficient immune response. The invading fungi will aid this process: the mycelium will detect microbes in the soil that help improve the tree’s immune system in case of attack, provided the former transmits a molecule informing him of the problem. For the moment, young Quercus is unaware of the relationship that lies ahead. All he knows is that the tips of his roots are under attack.

The hypha begins to insinuate itself between root cells, breaking down their organisation to form a bond stronger than marriage, called ectomycorrhiza. This is a perfect, inseparable welding of two very different organisms, the fungus and the growing sapling, which combine their cells to form an organ in its own right. Quercus ends up accepting the fungus inside his own tissues. But the fungus doesn’t stop there. Now that the connection has been made and the tree’s acceptance forced, Leccinum produces auxin, a hormone usually synthesised by plants to solicit the production of new tissues. By tricking Quercus once again, Leccinum orders him to make new roots, into which she will promptly insert herself, multiplying the exchange gateways. This involuntary production of root tissues has an energy cost for Quercus – but one that will very quickly be compensated, as we’ll soon see. The two individuals are now intimately linked, until death do they part.

In this story, the nodules of the rhizobium played an essential diplomatic role for the future of both protagonists. After Apodemus, this is Quercus’s second experience of direct exchange with a species completely different from his plant nature. This beneficial partnership has a name: symbiosis. In the symbiotic relationship it creates, Leccinum gathers sugars made by trees. Since the fungus pays in trace elements, the building blocks of these sugars, the exchange is largely agreed upon by the trees. These complex molecules are what allow them to grow. By entering into a relationship with several trees, it’s possible that Leccinum creates an underground relationship between young Quercus and his older parent tree, which stands, after all, only a few metres away. And so, this connection can be considered in two ways: as a divergence of water, trace elements and sugars destined for the older tree; or, as a conduit transporting help from the old tree to the new: a legacy, or even an inheritance.

* * *

The number of species of fungi in a given forest plot is considerable, but it is often difficult to inventory them exhaustively. Studies that count the fructifications, or caps, of fungi on reference sites in several French forests showed the emergence of new species, which had not been observed before, thirty years after monitoring began. Although not all fungi bear fruit, or not each year, more than a hundred different species can be counted in a single hectare, their hypha stretching out in all directions in the soil just below the surface. Each mycelium is generally dependent on one tree, but some know how to adapt, partnering with forest species other than the one for which they are programmed. When a hypha binds to a tree, the tree may be connected on the other side of its root system to another mycelium, which is, in turn, linked to other trees. This creates a vast underground network in which molecules circulate and can move from one tree to another, forming a highly efficient system of communication and resource-sharing that benefits all the connected individuals, no matter their species.

We often compare this network to the internet. However, the comparison falls short of being able to describe the totality of relationships and information that circulates via mycelia. Our internet functions for a single species, humans, and allows individuals to communicate and exchange extraordinary quantities of information. But there’s a great deal missing for it to be considered equivalent to the power of the mycorrhizal network. The latter goes much further, allowing the exchange of not only information but vital nutrient molecules between individuals of different species. In theory, if they’re connected to the same network, trees as far apart as several hundred metres can communicate, and even help each other in times of food scarcity for one of them.

As one of the new members of this vast network, Quercus is offered opportunities to develop and better resist the hazards he might encounter. This symbiotic relationship will be vital for him.

Quercus is still stuck in the brambles, but he has more than compensated for this handicap. With the help of Leccinum’s hypha, he now has access to an extensive, if somewhat anarchic, network. Leccinum is connected to many other roots of other individuals, mainly oaks. Some are young, like Quercus, but others, like Quercus’s parent tree, are mature. Up to thirty per cent of all the sugars produced by the trees are sent back through the sugar-enriched sap, called phloem sap, to the mycelium. The mycelium feeds on them and sends them throughout the network that forms it, allowing the most distant hypha to benefit and continue growing towards new volumes of soil. However, if one of the trees is in trouble or weakened, it can conserve its resources at the expense of the fungus.

Another advantage has been observed for trees: if one of them is attacked, it emits defence molecules and hormones, including some that circulate all the way to its roots. If the danger is sudden, the warning can even be issued via electrical impulses. This information is sent, along with carbon molecules, to the mycelium, which continues to redistribute it to the wider network. In this way, neighbouring trees are warned of potential danger. Quercus receives messages about the emergence of parasites or the dangers of various defoliators, and reacts by preparing for their potential arrival. He’ll be ready.

Quercus, an apparently solitary individual, has become an ultra-connected being, who seems to have access to everything this forest can offer. But while in Leccinum he has found an exceptional ally, other relationships are less happy. Quercus becomes sensitive to the approaches of more threatening fungi, such as oidium, or powdery mildew, which is found on the surface and attacks leaves. Most worrying of all, he is still not able to photosynthesise enough sugars because of this cumbersome bramble. Fighting to reach a little bit of light from inside his prison, in order to make new tissues he must instead gather sugars through his roots. Could the bramble, which had been his saviour, now be digging his grave?

HOMO, THE HUMAN, 1787

In which we discover the multiple unsuccessful attempts to limit the disappearance of our forests. Quercus may never succeed in extricating himself from his plant prison, the bramble. But we encounter a new ally, temporary perhaps, who will open the way for his upward growth. It is the beginning of a new era for Quercus.

The year is 1787.

Quercus is only seven years old, but his future is already in jeopardy. He needs photons to grow. Scarcely more than a few decimetres tall, the direct light he desperately needs is still blocked by a roof he could do without.

And that is not his only problem. The impact of human-kind on the area means that the forest is receding, as it has been for nearly seven thousand years. Logging is intensive, and Quercus’s chances of reaching the age of thirty are low.

This is not a promising scenario.

* * *

While Quercus has been trying to push through the bramble, Paris has been experiencing harsh winters and difficult living conditions. Even before his birth, the 18th century had not begun well: 1709, 1762 and 1766 were years of terrible famine, followed by very cold winters in the 1780s, which affected crop production. Could people use the forest to respond to scarcity? No. With ongoing wars calling for the replenishment of the Royal Treasury, and major works which required construction material, the forest was depleted.

Attempts had been made to regulate forestry activities in royal as well as private forests since 1552, under François I, but without success. A century later, First Minister of State Jean-Baptiste Colbert imposed the Forestry Ordinance of 1669 on the entire kingdom. This included the emergence of the first real forestry services and attempts to make inventories of forest resources. Quercus’s parent tree saw the first large-scale efforts to collect data about the nation’s woodlands, and the development of the first forestry management techniques.

But this had not prevented its exploitation. The proximity of our forest to Paris means that it was used for the construction of the famous palace in Versailles. And despite the century’s great famines, the country’s population has grown by thirty per cent over eighty years, which leads to an increased demand for wood to support the expansion of cities experiencing significant development.

More resources are needed, and Colbert’s ordinance is sometimes difficult to apply. In 5000 B.C., the afforestation rate in France was eighty per cent. Around 1780, the period when Quercus was likely born, the forested area had decreased to about twenty per cent. And its reduction isn’t over yet.

* * *

In the area surrounding Quercus, people have designed their environment to meet their needs – building homes, heating them, and finding food. For a long time, they’ve been cultivating the neighbouring marsh, just a few hundred metres away, which they drain by digging regular ditches. They also sow barley and wheat on the embankments in between – water supply is not a problem in this boggy area. Pigs are put to pasture on acorns in the forest, with people respecting the ‘right of pannage’ proposed by Colbert in his ordinance, which limits the number of animals allowed. The pigs are let into the underbrush where they glean what they can from the irregular production of the oaks. Heather is picked to make brooms and the thatch on houses. Sheep and cattle are grazed in an intermediate space between the village and the forest, where, every so often, fires are lit to regenerate the grass: the fires renew the grass’s nutrient content. People make every attempt to keep these fires under control, but now and then the flames lick the forest and the marsh, and sometimes blaze out of control.

Cattle are used for meat as well as milk production, and also help woodcutters transport logs out of the forest. These animals are sometimes brought all the way from the region of Beauce to help with this fastidious work in the spring, the calmer period for agricultural work. But in the Rambouillet forest, most logs are so heavy they can only travel long distances by waterway. What saves the large trees in this forest is the absence of major rivers. Rambouillet is at the top of several basins and its rivers are not large enough to allow for fluvial transport. So this forest is largely limited to a feeding role, and the livestock is numerous as a result.

But water is needed to quench the animals’ thirst. Ponds are dug so the animals can drink. In the forest is a transit post for the king’s messengers. A pond has existed there for several centuries, beside a house surrounded by walls. Within them, several horses can be seen grazing, awaiting riders from Versailles who, charged with royal missives, pass by and change horses. Given the frequency of grazing in the forest, another pond is created at the other end of the marsh. Because wild animals come here as well, today it’s called the ‘Mare aux Biches’, the deer’s pond. A sandy path between the marsh and Quercus allows transit between the local village and the larger town in the forest to the west.

Tucked away inside his bramble, Quercus is a hidden witness to the many riders, travellers and carts that use this path each year. But these various activities are not the only things to shape the landscape of our forest. Kings love to hunt – François I is an illustrious example – and so the forests must abound in game. Here we find wild boar, stags, deer, hares and rabbits, which the forest verderers frown upon, reproaching them for eating the bark of young trees and ruining attempts to plant more.

Inside his bramble, Quercus is safe from these threats, but he still can’t reach the much-desired light. The risk grows daily that he’ll never break free to become a large tree dominating the forest. But, with humans’ need to control everything around them, to master even the landscape, they have invented a system that might well be what saves our young oak. The time has come for them to intervene.

Quercus is to benefit from a very rare tax, applied in just a few royal forests, and which will soon be eliminated. Under this decree, neighbouring villagers are allowed to bring their animals to graze and gather some firewood and, in exchange, the king demands a forest worthy of the most beautiful paintings, with large oaks beneath which he can be seen galloping in pursuit of a noble and majestic stag. By incredibly good fortune, the ruling covers the area where Quercus struggles towards the light.

* * *

Quercus’s leaves seek out every photon that manages to penetrate the shade. For a while now, he hasn’t really grown much. The only thing keeping him alive is the infusion of sugars from Leccinum. Suddenly, one day the grey shadow becomes an abnormally deeper darkness. The sun disappears. It’s blocked by a man, hovering over his bramble. Quercus doesn’t see this directly, but his photosensitive cells detect the change. The man examines the prickly plant, and makes out a few oak saplings within it, just waiting to be freed. The expert blade of the silviculturist trims the top of the bramble to help the future trees emerge, conserving the branches around them to ensure their protection against herbivores. Later, when these trees are grown, the tables will be turned. They will extend their foliage, creating such significant shade that the bramble will die for lack of light. The competition for photons is a matter of life and death.

The silviculturist’s shadow disappears as he moves on to the next bramble. For the first time in his life, Quercus is hit by the sun’s direct light and warmth. The rays from the sun allow him, finally, to begin the set of chemical reactions for which he’s programmed. His future begins to brighten. He is born a second time.

The presence of his parent tree a few dozen metres away is not obstructive, nor are the nearby clumps of coppice. There is nothing above him, nor immediately to the south, the direction from which the maximum number of photons arrives in the middle of the day. All he needed was direct light, and now he has it! He’s not alone in this bramble; other oak saplings have also been freed. But despite being barely a metre in height at the age of seven, Quercus is already the tallest, and he’s hardy, too.

Foreign sugars are drawn upward towards the apical bud, the bud right at the top that leads to the production of tissue reaching towards the sky. Grow, reach the light before the others. Defy gravity. If Quercus were alone, he would have developed low branches very quickly and stretched out. But because there are several saplings in a one-to-two metre radius, all waiting for an opening in the bramble, the race towards the sky is on. The various shoots of these siblings grow by girding each other, favouring their crowns at the expense of leaves that might have developed along the trunk. Friends for a time, they support each other today, but will likely be in competition tomorrow, when only one adult tree will win out in this ecosystem.

* * *

Even today, Quercus retains the memory of this history. His current architecture, with his long, straight bole, indicates to the forester that the tree began growing alongside other trees, long since dead.

While things are stabilising for Quercus as he begins his upward growth, everything is about to change for Homo. Successive great famines will weigh heavily on the local serfs who will soon revolt against their king and the rest of the privileged classes. After the start of the French Revolution in 1789, forest management regulations will be blown to pieces. People will come and take what they need from the forest – wild game, wood, anything that might sustain their lives. Dangerous times lie ahead.

QUERCUS, 1810

When he’s thirty years old, Quercus begins to take on the typical shape of an adult tree. We discover that his structure is quite simple, in the end. And that, within the roots, trunk, branches and leaves, physical and chemical laws operate which may be basic, but which make the whole organism very resilient – solid and flexible at once. We meet the plant world’s best ally, an ancient bacterium with an inexhaustible drive to produce energy vital to the tree’s growth.

The year is 1810.

When a tree grows a branch, it is to fulfil a particular function; mainly that of gathering solar energy. Its position gives us a page in the history of the plant’s life. A large branch only a few metres up an adult tree would have emerged early in its life. By trying to understand the architecture, we can map its history. The structure of its tissues – especially the wood – is a lasting record of its ‘choices’.

* * *

The French Revolution blew apart forest management and all available resources were pillaged. In particular, felled timber, twigs and coppice, and forest fruits were stripped, and wild game was hunted tirelessly. But when the Reign of Terror of the early 1790s ended, Napoleon Bonaparte reinstated a forest service that regulated use of the woods. Once again, the need for timber to build ships and extend cities required concerted silviculture. Our oak probably benefits from this official decision.

Quercus is thirty years old. Because his early growth was restricted by the bramble and the harsh winters, Quercus is still only a dozen metres tall, and barely ten centimetres in diameter, but already his form can be seen.

His shape emerges gradually. The roots continue to grow. According to their species, tree roots may either stretch out laterally below the surface or favour depth in order to access groundwater. Their structure follows a model fairly similar to that of the trunk, except they can slow their growth depending on any obstacles they encounter. Quercus relies on a prospection of the soil that is lateral as well as deep, and still benefits from the help of Leccinum’s mycorrhizae, which continue to stretch ever further and provide him with resources from the soil.

Quercus continues to reach towards the sky. He will only stop growing when he can no longer carry nutrient-rich water to the furthest branches of the canopy. To be as efficient as possible, he regenerates the tissues that carry his sap each year, those towards the outside of the trunk. The sap-carrying tissues depend on those at the tree’s centre, which constitute the heartwood (also known as duramen). These die off as the tree develops and sometimes act as reserves of sugar and starch for the end of the following winter. Thus, the heartwood inside the trunk is in fact dead tissue, protected by the live tissues just below the bark, which continue to grow.

Although it is the dead part of the tree, the heartwood remains essential. It is what allows Quercus to defy one of nature’s great laws: gravity. Without the heartwood, the tree would flop towards the ground. All through the heartwood, the xylem, or sapwood, and its large springtime vessels carry raw sap – which is to say water, simple carbonaceous molecules and trace elements – from the roots to all the other organs of the tree and right up to the canopy. The phloem forms the layer of tissue supported by the xylem, initially very simplified and referred to as ‘primary’ phloem, then much more structured once the warm season sets off the abundant production of material, when it becomes known as ‘liber’ or ‘secondary’ phloem. Its job is to redistribute the sugar-enriched sap, called phloem sap, issued from the leaves, which descends towards the roots. The cambium is a layer of cells between the xylem and the phloem, whose role is to produce cells for both these sap-transporting tissues, on demand. Finally, the bark is made up of phelloderm, protective cork, and the epidermis. Between the cork and the phelloderm is another layer of generative cells that provide the bark with new cells.

For Quercus, the bark forms thick bands with deep crevices in between. Higher up on the tree, the branches follow this pattern of superposed layers of tissue, all the way to the terminal bud of each branch – also called the meristem, whose primary function is to guide the tree’s growth towards the light, from the moment of its birth. If we could hear these buds, they would be constantly calling out to the elements that support them: ‘Follow me – the light and its precious photons are this way!’ In general, young branches have a layer of cells in their epidermis possessing photosynthetic chlorophyl, or chlorenchyma, to support the work of the leaves, particularly during spring. Finally, this long and fastidious description ends with the crown of leaves.

Every year, the tissues that were previously made – all those vessels, supportive elements and parts that transport materials, in which circulation is very dense – are abandoned and overlaid by these new tissues, which are adapted to the current conditions. If unlimited resources are available, water in particular, the vital fluid highways are wide. If it’s dry, too cold, or if the tree is too constricted by neighbours and forced to compete for essential resources, the fluid flow networks are tight and narrow, to limit the difficulty of supplying different parts. The wood gives us a map in the form of rings made up of these raw and elaborate sap-conducting vessels. The tree grows wider and taller with the support of the dead parts it encompasses.

* * *

The roots, branches and trunk represent nearly ninety-eight per cent of the total biomass of our tree. The remaining two per cent – the leaves – are essential, however, for making it all work, and for the production of Quercus’s constituent materials. Once the plant machine’s equipment is established, the chemical production factory is put in motion. Quercus won’t stop transforming simple molecules into complex molecules. All the tree’s tissues are used in the effort.

* * *

The leaves are the engine of Quercus’s production. The chlorenchyma of the bark contributes, but only a very small part. In this species of oak, the leaves grow at the ends of the branches and are lobed and round, with pinnate veins, meaning one central vein that serves several secondary and lateral veins. Between them, the leaf blade forms a sort of green fabric, a soft and slightly fluffy sheet to start with, which soon grows rigid and firm, so as to better resist the ravages of time and make up this plant tissue rich in chloroplast-bearing cells, the chemical agents of the tree. Stomata, a kind of pore, act as windows opening onto the surrounding air. The whole leaf is held by a petiole, a stem which in this species, the sessile oak, is several centimetres long.

While a very old deciduous tree may have nearly eight hundred thousand leaves, Quercus already has more than ten thousand. Each leaf constitutes a nerve centre, acting as both an entryway and exit into the atmosphere, a kitchen which produces food for the supporting tree, a hospital to produce reparative molecules for damaged tissues, a detention centre for harmful molecules, and, in the event of attack, a communication centre to alert the entire organism to the danger. Additionally, it is a factory, manufacturing weapons that might be needed to defend the whole organism. The leaf knows how to do absolutely everything. So simple in appearance, it hides its complexity well.

By the time of the bud break – when Quercus unfurls his leaves in the spring – the activation of all his organs has already taken place. The tree asked for water first, before any other nutrient. Then the chlorenchyma, with its few chloroplasts housed in the epidermis of the branches at the top of the tree, helped to begin sugar production as the tree awakened, which set off the the rest of the plant’s machinery. But because he still didn’t have the means to transform simple molecules into sugars, Quercus had to rely on his stored reserves of starch and sugars, such as saccharose. Starch is easy to transform into other sugars and quickly served him. The water that arrived through the roots then carried these nutrients to the top of the tree, all the way to the buds. All of this constituted the first energy input for the production of leaves.

The leaves contain chloroplasts, former bacteria that were engulfed by leaf cells. On a bacterial scale – in the realm of the micrometre – these are the definitive chemical factories for Quercus, but also for all plants that populate our planet. Each of these factories makes so many molecules, you’d think you were in a manufacturing complex, with workers toiling around the clock to produce the goods.

In a nutshell, the chloroplasts gather water from the ground, carried from the mycorrhizae, then open the stomata, the leaves’ entryways and exits, to catch carbon dioxide from the air. Then, thanks to photons from the sun’s rays, the two molecules of water and carbon dioxide are completely taken apart, atom by atom. The chloroplast then builds new molecules – carbohydrates, mainly glucose – and sends the waste products – water and oxygen – into the atmosphere. To succeed in this amazing feat, the worker – the chloroplast – uses a tool that resembles the solar panels that blossom on our rooftops today: a photosynthetic pigment called chlorophyl, capable of using light energy from the sun to activate electrons that stimulate chemical reactions. At the heart of the chlorophyllic system is magnesium, an element with a happy tendency to free oxygen atoms, to which it easily binds. And, to accelerate all the processes of molecular transformation, Quercus uses enzymes. Thanks to these enzymes, each chemical reaction happens in only a few microseconds. These occur everywhere in the tree, from leaves to roots.

Thus, the principle of photosynthesis is the transformation of carbon dioxide and water into oxygen and sugars. Its energy yield is lower than that of solar panels, but it has the advantage of being very low-cost and of renewing itself endlessly. The energy produced can be stored and redistributed when the tree needs it most, sometimes several weeks after production. These thermodynamic reactions become more complex as chloroplasts also know how to make other molecules, using trace elements from the soil, to respond to the various demands of the multi-faceted organism that is the tree. Indeed, if a root shows a deficiency, if a nearby leaf needs extra starch to repair a leaf blade damaged by a shock or a parasite, or if the tree is under attack, information is transmitted from the affected tissue to the cell housing the chemical factory. Sap plays a crucial role here, circulating throughout the organism, delivering the nutrients and information needed for this complex life.

* * *

The functioning of the superstructure that is Quercus depends on vital fluids. As is the case for every living being, the circulation of nutrients is only possible in liquid form. And here, gravity will pose a problem for Quercus. Although the phloem sap, full of sugars and other molecules made by the chloroplasts, can easily descend from the leaves to the roots, it’s not the same story for raw sap, which must rise from the roots to the crown. Animals rely on a pump to disseminate vital fluids, such as the heart in mammals. But a tree has no pump. So what does it do? How does it defy gravity?

Nature has given Quercus and all trees three tricks that enable the upward movement of fluids. The first uses osmotic pressure. When you add two liquids together, the one with the highest concentration of dense molecules tries to mix with the other, as though to relieve itself of the weight of these molecules, which are then redistributed among both liquids. They aim for what is called osmosis. Relying on this physicochemical rule, the tree always offers a fluid with a low concentration of heavy molecules to its crown. And this is quite logical, when we consider that these molecules, made up of trace elements drawn from the soil, are progressively distributed to all the tree’s branches. The sap gradually unloads as it rises toward the treetops, becoming lighter as it climbs. In this way, the raw sap carrying nutrients always seeks to merge with the molecules of sap just ahead of it.

But this mechanism alone is not enough. To complement it, the vessels are constructed to favour capillarity. It’s a bit like in a glass: when it is filled to the brim, you can see a film of water extending beyond the rim, because of the capillary forces of the material. The vessels of the sapwood have walls mainly made of lignin, a tannin-based material, one of whose properties is to be water-repellent. Lignin repels liquids – it cannot do otherwise. This means it promotes the circulation of liquids, and the sap can rely on it to move upward. This force helps draw all circulating fluids towards the top of the tree.

The third and final system in place is supremely intelligent. It requires absolutely no effort or redistribution of liquids, as might be required by scientific chemical calculations, nor properties involving the construction of tissues. This time, the tree lets nature take its course: the trick is to call for upward flow simply by opening the valves and allowing the fluids to circulate as much as possible. We’ve already seen how, when the leaves produce sugars and different complex molecules, they emit oxygen and a small amount of water to balance the chemical formulas. When the leaves see that raw sap fluids are arriving, they send the molecules that have been made towards the bottom of the tree, via phloem sap through vessels in the phloem.

Remember, the osmosis of the first system allowed for trace elements and water to be drawn towards the top of the tree, involving a dilution of molecules in the raw sap, a dilution that grows stronger as the fluid climbs towards the top. For this principle to function, an enormous amount of water is needed. The tree is the inventor of the water pump. A thirty-to forty-metre-tall adult oak pumps up to two hundred litres of water from the soil per day. The raw sap generally rises at a speed of a few centimetres an hour. When it has a low concentration of trace elements, the speed can reach up to seven metres an hour. But when all these water molecules arrive in the leaves, they can’t all be used, and Quercus must deal with the surplus – if it hangs around too long, the excess water is at risk of altering leaf cells. The excess water is discharged through the tree’s crown into the atmosphere, via the stomata, in the form of water vapour.

This gives rise to the water cycle so dear to our forests. Water is pumped from the ground, redistributed throughout the tree, and climbs all the way to the leaves. One part is deconstructed to make sugars and other volatile molecules, another part serves to redistribute these molecules to the tree, right down to the roots, and a large part is discharged into the air in the form of vapour. As a result of this phenomenon, forests distribute water into the atmosphere. Up to thousands of litres per hectare each day. Just as leaves are tree factories, trees are cloud factories.

* * *

Quercus’s water engine is extremely simple and requires very little energy to circulate fluids. All he needs is for direct sunlight to hit his leaves. But the atmosphere is saturated with spores, pollens and seeds. Up to five hundred particles might be deposited on Quercus’s leaves each day, blocking his stomata, or creating a thin film that reduces the efficiency of photosynthesis. He must not let a few particles on the leaf blades jeopardise his survival! To deal with this, Quercus has developed a fairly simple cleaning apparatus. The tree produces very fine hairs along the veins, sheltered from the rain on the underside of his leaves, called domatium, invisible to the naked eye. This pelt serves as shelter for microscopic dust mites that feed on this organic dust. Nothing must slow photosynthesis.

To take maximum advantage of the light, Quercus must extend his network of branches. If he had grown up in a very open environment, on the neighbouring heath, for example, or in a large crop field, he would have been able to reduce his height growth, shortening the distance between the roots and the leaves. But competition with neighbouring trees, particularly his siblings, requires Quercus to climb, growing his trunk first so he can get closer to the sky. At some point, his growth will inevitably stop, because the three physical principles allowing the upward movement of fluids will no longer be sufficient to transport the raw sap all the way to the crown.

Quercus experimentally developed leaves on his first few metres, but none had a durable function – they tend to disappear as he grows. And so he keeps extending upwards. First, a straight and solid trunk. At six metres, he was able to develop a shoot that would become the master branch, because of an opening in the foliage. But above, there is no other choice but to wait more than eleven metres before presenting a first major separation, a division. Two metres higher, just below the terminal bud, there is another division. A small one. But one that, in a few years, will give rise to two main branches forming a clear fork, while a third branch will extend laterally towards the north. However, there’s less sun on that side – the south is much more favourable. This branch will seem more fragile later on. Perhaps a poor choice on Quercus’s part? But at the time of this new development, the leaf cells cannot yet detect any abundance of photons to come. The opening in the foliage enabled this cellulosic gamble, and the tree bets on potential, on a possible future for this new branch.

* * *

Little by little, each constituent element of Quercus reacts both holistically and almost autonomously. A branch can respond to various stimuli; one branch on the other side of the crown might respond to very different stressors in its local environment, because its exposure is different, or because it is more or less impacted by the wind. In this way, Quercus builds himself. But make no mistake – he is not just a plant. Like the other trees in the forest, Quercus is a being made up of a multitude of individuals – each limb and branch fed by the same trunk. Each part of the crown is almost independent of the others. So the tree’s evolution in space is propelled by opportunism, often as a result of the death of a neighbour, which an adjacent branch might profit from. One’s sorrow is another’s joy. Quercus is a multiple being, a sort of plant explorer.

* * *

This is how the familiar shape was formed, the one I see today each time I visit Quercus.

TORTRIX, THE CATERPILLAR, 1820

In which we discover that the emergence of Quercus’s tender leaves offers highly sought-after food opportunities for many organisms, including Tortrix, a small caterpillar with an insatiable appetite. Quercus will pay the price. We learn that Tortrix is still a fragile animal, and that only these leaves will save her. We understand that, as a rooted organism, the tree must search deep within to defend against these multiple attacks. But, for the moment, Quercus suffers.

The year is 1820.

The underbrush is lit by the first rays of spring sun falling on the last winter flowers, the ones that have chosen to emerge early before the trees’ leaves filter the light. First among these are purple hyacinths and white anemones. The forest is multicoloured and rich in tangy, sweet scents, released by a light morning dew that covers the wild grasses with sparkling droplets. Insectivorous birds, most of them migratory, are returning from Africa where they spent a more clement winter than the one here in Europe, and declaring loudly that, yes, they do intend to reclaim the territory they acquired last year. They’re here to reproduce, and the toughest among them have claimed the areas richest in food. For the insects, the birds’ appearance chimes the hour of danger. They must remain hidden, even as they rush to complete their biological cycle: emerging from the egg, growing through the larval stage, moulting and transforming into an adult. Their adulthood sometimes lasts for only a few hours – just enough time to meet a sexual partner. It is a life governed by the seasons and one central challenge: avoid insectivorous animals.

But how? They’re plentiful and voracious. Fortunately for them, it’s unlikely that insects feel fear. In this rapid cycle of eating to grow, and growing as fast as possible before they reproduce, there’s no time for philosophical questions.

And now for a meal. Tortrix is hungry.

The freshly-built limb is so welcoming, so delicate, soft, and rich, made only of trace elements and water. So tender, and nutritious too. The caterpillar is programmed to eat oak leaves. And she’s right on time. Nature has regulated her biological rhythm so she will respond to the emergence of the leaves. She is primed for a growth spurt.

* * *

Her mother laid tiny eggs on the bark of Quercus’s boughs last summer. The tree was not aware of this, since these eggs are only on his epidermis. Tortrix waited inside her egg all autumn and winter, until the weather was favourable enough to emerge. Early April this year brought the ideal conditions: relatively mild temperatures since March led to the gradual opening of the buds on the oak. The buds were protected by a sticky substance, a wax which enabled them to resist the freezing of the subcutaneous tissues that hold the new leaves, still folded up inside. Now, the scales of the bud Tortrix has chosen have come unstuck, and the caterpillar in the first larval stage tucks herself inside to take advantage of this essential meal. If the winter weather had been colder, the oak might have waited longer before the bud break – when it opens its buds and makes its leaves – and the diurnal caterpillar of this green oak moth, Tortrix viridana, would never have been able to properly develop. This is why Tortrix populations have years of low numbers as well as boom years. The mild temperatures of this early spring are a good omen for Tortrix and her peers.

* * *

After passing through the recently-opened bud to taste the tender new tissues, she took advantage of the almost simultaneous emergence of the oak’s first leaves. When Quercus felt the time had arrived for the leaves to emerge, he reactivated the circulation of vital fluids within them. The chlorenchyma of the young branches helped him create the first sugars necessary for the opening of the buds, and then make the new spring leaves. They’re beautiful, so efficient in their endeavour to draw liquids from the ground and up to the top of the tree.

The tree has renewed his connection with the mycelium and with it, the flow of water through the tree has picked up pace, moving reserves of sugar and starch stored in the deep roots and the taproot up towards the crown. These reserves support the builder branches and buds, and the simultaneous creation of Quercus’s first sapwood cells, those large, raw-sap-conducting vessels. Long before the visible bud break, Quercus had already been coming back to life.

* * *

Tortrix is programmed to emerge from the egg when the photoperiod – the quantity of daily light – signals to her that the oak is about to bud and the leaves will be out very soon. Illumination is the life source for the tree, but also for its enemies. The advantage of eating newly-formed leaves is that they are extremely tender and digestible. In the first days of their formation, the tree is drawing upon its energy reserves to produce plant tissues. It makes them as quickly as possible, so the leaves can take over from the reserves and photosynthesis can instead fuel tissue production. Once they have grown, the leaves will have the job of making defence molecules, but meanwhile, they are fragile, vulnerable and full of simple trace elements, which are easily assimilated by our caterpillar. And Tortrix cheerfully takes advantage! She feasts as fast as she can, before Quercus can sense an attack, identify the enemy and react.

After the buds, Tortrix heads for the leaves to devour their blades, one after another. Previously camouflaged inside the bud, she’s now highly visible on the leaf – only her green colour hides her from predators and other parasites. Tortrix is not alone. Thousands of other caterpillars have, like her, begun their development in sync with the opening of oak bud scales. In turn, species that eat these insect larvae have synchronised their reproduction with the caterpillars’ anticipated date of emergence. This is the case with birds such as tits: their chicks are so voracious, they need to be continuously fed. A single couple captures more than five thousand caterpillars in just three weeks to feed their nestlings. Nearly a hundred species of insects hunt caterpillars, or even parasitise them by laying an egg inside them. The larva of an ichneumonid Hymenoptera, from the very large family of wasps, can develop inside our caterpillar and eat her viscera while she’s still alive.

But Tortrix has one significant advantage: numbers. This year, the green oak tortrix is dominant in this forest, but there are other species as well. For the most part, they too have calibrated their phenology, in other words their rate of emergence and subsequent development, to be able to take maximum advantage of the most tender leaves. In some oak groves, up to 1,100,000 caterpillars can be counted per hectare of forest, from a wide variety of lepidopteran (moth) species. That’s nearly eight tons of caterpillars per hectare. So all Tortrix has to do is melt into the crowd!

And that’s not even counting all the other insects, the Coleoptera (beetles), the largely dominant Diptera (flies) and Hymenoptera (wasps, bees and ants), which can, in exceptional years, amount to nearly seventeen million flying and crawling insects per hectare, in the richest and most diverse forests. This astronomical number reflects the high level of animal activity in the forest. The higher the forest population, the more insects there are – up to nine times more in the canopy than on the ground. Indeed, it’s common, especially on calm spring days with no wind, to hear the canopy veritably humming with the activity of flying critters. With this exceptionally high number of insects, Tortrix has a good chance of avoiding the risks of predation and parasitism.

* * *

So, she nibbles avidly at the leaf on which she’s perched, avoiding the harder veins in favour of the much more digestible tissues. She eats and eats and eats, growing longer and fatter. Like the hungry caterpillar of the children’s story-book, Tortrix is insatiable. At this stage in her development, she is, above all, a digestive tract: she eats, digests and defecates for most of each day. You can walk through the forest in May, under a completely blue sky, but still hear a sound like rain. This is from the falling exudates of our caterpillars – their droppings – made up of undigested potassium, nitrogen and phosphorus concentrates. Depending on the number of caterpillars, up to three hundred kilos of droppings have been measured per hectare, in some cases doubling the soil’s nitrogen content. Add to this the plant debris that falls from the treetops – the casualties of their gluttonous consumption – which promotes the development of soil bacteria.

In this way, a large portion of the trace elements so vital for Quercus’s growth are redistributed to him in highly concentrated form. These trace elements pass through the phases of molecule degradation, and then absorption into the ground via various decomposer microorganisms, before being collected again, namely by Leccinum. In the forest, nothing is lost, and everything is recycled.

But meanwhile, Quercus’s leaves are disappearing as quickly as he can make them. His chemical factories may be working full tilt, but Tortrix represents a significant and immediate threat for our tree, preventing him from photosynthesising the molecules he needs to continue his annual growth, let alone begin making the reserves he’ll need for next spring’s bud break.

By the time they’ve finished growing, caterpillars reach a length of fifteen to eighteen millimetres. Then comes the pupation phase. Tortrix has a feature that makes her recognisable from afar – in this phase, she rolls up a leaf – yet another one that Quercus won’t be able to count on this year for photosynthesis – which she has previously selected. This is where she gets her name; from torsion. Tortrix has spent nearly a month eating holes in as many leaves as she can, but she is entering a fairly fragile period and so the chosen leaf must be intact to ensure the necessary protection.

When the leaf is rolled up and stuck together with sticky strands of silk Tortrix has made herself, she slides into the chamber to begin pupation. Slowly, she wraps herself in a chrysalis. And then something magical happens: all her viscera are reorganised in a sort of melting-down process, and soon an amorphous mush can be observed inside the chrysalis, from which a green and grey butterfly, with a twenty-to twenty-five-millimetre wingspan, will emerge sometime after the beginning of July. This butterfly will take flight, find a partner and reproduce. A new cycle will begin.

* * *

For Quercus, the destruction of the leaves and buds slows photosynthetic production, and thus the tree’s capacity to produce wood and reproductive systems – the male catkins and female flowers. He is able to make replacement leaves, but if the attack is too massive or if it’s repeated, the tree won’t be able to reproduce, because he won’t have enough energy to make acorns. Also, Quercus has now consumed all of the energy reserves in his taproots. This time around, the tree will need to make more leaves without the precious reserves he had saved. This presents a considerable energetic cost for Quercus, with a knock-on effect the following year. Tortrix’s abundant numbers can have serious consequences.

It seems that some trees ‘learn’ to defend themselves against this sort of attack. Last spring, I visited Quercus to breathe in the first scents announcing the return of life in the forest. The birds began singing at dawn, creating an almost intoxicating symphony whose orchestral organisation my novice ear could only partially discern. Quercus’s bud break happened late, more than two weeks after neighbouring trees of the same species. We sometimes see a discrepancy of up to three weeks between bud breaks of branches on the same tree. Although conditions may be favourable, some branches hold back, almost as though each one can ‘decide’ on its right time to open. It seems that this adaptive phenological response is a reaction to make it harder for caterpillars to attack the buds.

* * *

Ever since he sprouted his first few leaves, long before the French Revolution, Quercus has been adaptive. By budding late, he convinces Tortrix’s descendants to switch to neighbouring trees – these, in contrast, are budding earlier in an attempt to take advantage of the extra spring sunlight allowed by Quercus’s slower growth. Quercus’s strategy is risky, because it means the quantity of sun he receives – and therefore the amount of photosynthesis he performs – is reduced. And yet Quercus remains the dominant tree in this part of the forest. So far, his gamble has paid off.

NEMOBIUS, THE CRICKET, 1820

While Tortrix is producing vast quantities of droppings which fall to the ground, Quercus recoups a good amount of their molecules, helped by the multitude of microorganisms that live in the humus. We encounter the primary decomposer par excellence, Nemobius, who dominates the underbrush. This insect’s life oscillates between breaking down waste – dead leaves in particular – and avoiding predators who take advantage of the teeming crowd on the ground.

The year is still 1820.

The caterpillar excrement that falls from the trees in spring is transformative for many soil organisms. The world of the forest bed – the humus – is populated by bacteria, viruses, myriapods, nematodes, springtails, fungi (more mycelia), earthworms, crustaceans, gastropods and insects, whose density per square metre is staggering. Protozoa, nematodes, tardigrades, rotifers and copepods alone represent up to four hundred million individuals per square metre of forest soil. Larger creatures, including some worms, mites and springtails, can average up to five hundred thousand per square metre, sometimes nearly double in the richest, most diverse habitats. Finally, the giants in this group of the infinitely small – creatures more than three millimetres long – can number several hundred in the same volume of soil. Suffice to say that the forest floor, despite how peaceful and still it appears, is absolutely teeming with fauna, fungi and other organisms, all constantly in action.

These organisms break down the elements falling from the sky, but not only that. The world of the forest floor holds the primary decomposers, who break down leaves whole or in pieces; secondary decomposers, who break down complex molecules and then redistribute them; parasites; predators; and a whole host of other species that benefit from this little world. Enchytraeids, or forest earthworms, ingest the almost-completely decomposed material and finish grinding it down in their digestive tracts, leaving behind castings of earth and broken-down organic molecules, the perfect mix for a subsequent absorption by Quercus’s fungal friend Leccinum. Worms also aerate the ground, digging tiny tunnels as they wriggle, allowing air to circulate throughout the soil. All living organisms benefit from this action because they, too, need oxygen. But the equilibrium is delicate: the smallest event – an overturned stump, a patch of grass, an opening in the canopy that suddenly lets light in – can upset this infinitesimal world and throw its inhabitants into a panic.

Among these critters is Nemobius. Born last year in this very spot, the cricket stayed hidden deep in the leaf litter to avoid winter’s frost. In spring, as soon as the plants came back to life, he got to work breaking down dead leaves, while Tortrix was beginning to develop in Quercus’s foliage. Soon, the caterpillar will offer Nemobius a new delicacy.

Nemobius sylvestris, the wood cricket, is a distant cousin of grasshoppers and locusts. When the ground has warmed up, it’s time for Nemobius to reproduce. His own life will be over when this second growing season comes to an end, and so it’s imperative for the cricket to provide the forest with future generations of decomposers.

Nemobius uses song to seek a mate – he stridulates, rubbing the femurs of his front legs against his abdomen to produce a little tune, a song that to human ears begins melodiously enough and quickly becomes grating with its regular, relentless stanzas. Singing is a risky activity – although it does attract sexual partners, it also signals the cricket’s existence to other animals in the leaf litter. Nemobius must avoid being devoured by voracious predators such as the ground beetle, a Coleoptera that cannot fly but races through decomposing leaves in search of prey. A real super-predator, this beetle is a ruthless insect and slug hunter. Nemobius must also avoid spiders such as the wolf spider, Pardosa lugubris, which can hunt even while carrying a nest full of eggs on its body. And then there are land mammals such as shrews and moles. In short, Nemobius’s daily life is no picnic. But despite the risks, the cricket must continue to meet the basic requirements of its condition as an arthropod – eating and reproducing.

Having chosen a small area of a few square metres, he spends most of his time eating dead leaves. Nemobius is the first in a long series of decomposers. The next ones will feast on its barely-digested faeces and many leftovers – Nemobius is not very skilful with his mouthparts and scatters bits everywhere. But without the cricket, breaking down all the material that falls from the trees would take much longer and require hours of mechanical work – animals passing by and breaking up the dry leaves with their hooves – or would mean waiting for rain, which, when heavy, can break molecular bonds as it falls on already-fragile, thin dead leaves.

Normally, Nemobius must content himself with the fallen brown oak leaves from the previous year. They’re not very tasty, but when it’s all you’ve got to munch on, you make do. This spring, though, the cricket can enjoy bits of fresh leaves the caterpillars have let fall, the young leaves still low in tannins which are much easier to digest, as well as the ultimate treat: nitrogen-rich caterpillar poop.

This rain of nitrogen droppings also stimulates the bacterial life of the soil. Bacteria multiply rapidly and help break down complex molecules. At each stage, enzymes – proteins with catalytic properties, capable of dissolving other molecules without altering themselves – accelerate the chemical processes of molecular decomposition. The final product of these successive processes of decomposition is then redistributed to the rest of the community. When the broken-down molecules continue on their path through the decomposing leaves to the ground, the hyphae of various mycelia can simply help themselves. This is how, in just a short cycle, Leccinum retrieves a large amount of the nitrogen Tortrix diverted from Quercus and redirects it to the tree. In just a few weeks, we’ve come full circle.

Depending on the nature of the stony ground below the leaf litter, both in terms of its composition and acidity, Nemobius and the microorganisms break down the organic matter, to a greater or lesser degree. Further on, the heather of the adjacent heathland allows a glimpse of a sandy geological layer, here one hundred and thirty metres deep, called the ‘sands of Fontainebleau’ after the place where it was first described. Sandy ground is very limiting for forest development because its nutrients and water are so sparse. Only a few birches have managed to establish themselves here – not a promising sign for Nemobius’s development. By contrast, deposits of silt in the ground beneath Quercus enrich the soil considerably, promoting the underground path of deciduous roots. The leaf litter of oak leaves is microorganism-friendly. Together with the debris they decompose, microorganisms form distinct layers of soil which we call the ‘humus’. This humus has a specific name: moder. Despite the ground’s acidity, the little critters in the underbrush do their good work and break down the organic matter rather well, rendering it, at the end of the chain, more easily assimilable by Quercus. So, while they may seem insignificant, these tiny species are absolutely essential to trees.

Today, when I come to sit at the base of Quercus, I often hear the strident concert of Nemobius and others of his kind. It is especially loud on hot afternoons in high summer, when the birds have returned to their nests to rest and escape the heat. The tree canopy provides a dappled shadow, allowing light to pass through, but lessening the intensity of the sun’s rays, which would otherwise overwhelm the tiny inhabitants of each soil plot. The underbrush remains a pleasant place to be, and Nemobius’s call is a reminder of the extent to which the forest fairly teems with often unsuspected life.

QUERCUS, 1840

In which we learn that parasitic attacks on trees are so numerous and varied, they require more than a single ‘immune’ response. We discover how Quercus will learn from these assaults and adapt with counter-measures including luring his enemies, and setting up defence systems that are almost disconcertingly simple. Sometimes the best defence is to attack. We understand how chloroplasts can produce toxic chemical weapons, all while ensuring the transmission of information through the air to alert neighbouring trees. We discover that this chemical arsenal adds to Quercus’s good health, and that we humans benefit from it as well.

The year is 1840.

By letting pieces of young leaves fall along with nitrogen-rich excrement, Tortrix helps enrich the soil on which Quercus depends, but at the expense of the tree himself. This sort of biological paradox doesn’t faze nature: the inhabitants of the forest are used to it. In the aftermath of the caterpillars, light filters through the thinned foliage of the oaks and inundates the underbrush, where the shrubby and herbaceous vegetation will benefit from precious photons.

The defoliation means that Quercus has to gather all his energy to make new leaves, rather than making the molecules necessary for other functions, for example, building up precious reserves of starch and sugars, particularly saccharose, which will be helpful for the following year’s bud break. These reserves are distributed across the woody parts of the tree, from branches to roots, as soon as the tree has enough leaves to begin making them. In times of hardship, these sugars can be transformed to help build new tissues or defences. In autumn, these molecules are carried to the root phloem and from the tap root to the base of the trunk. On one hand, they will serve as reserves close to the area where activity resumes in spring, as the roots receive the first drops of water. On the other hand, they protect these particularly sensitive tissues from frost, because starch is a good thermal protector.

By mobilising his resources for regrowing leaves rather than producing reserves, Quercus has made himself vulnerable to the climatic hazards of the coming winter. Indeed, although his trunk is straight, it shows a longitudinal lump that begins at the ground and stretches upward over three metres. This is a sign that his tissues froze when he was young, causing the bark to burst open in this spot and forcing the tree to protect himself by forming a bulge to cover the wound. Several neighbouring trees show the same wound, the scar of an event in the distant past that affected the whole forest community. It’s possible that this forest experienced several episodes of massive springtime defoliation which prevented the trees from making precious energy reserves, followed by periods of winter freeze.

Quercus doesn’t have a nervous system. ‘Feeling’ an attack and reacting is not an easy thing for a plant. However, even though we don’t completely understand the biological mechanism, we know that the tree keeps a memory of this event. Now that Quercus has grown into a tree that towers over all his neighbours, casual observers might believe his success is due to an early bud break each year, gaining a few more days of sun to make the tissues and leaves that rise above neighbouring treetops. But we have seen that, on the contrary, it is by budding late that Quercus protects his leaves while his neighbours fight against the incessant nibbling of the caterpillars. If they attack Quercus, Tortrix’s descendants could even perish for lack of food, as it remains inaccessible, double-locked inside still-tight buds. The plant’s very simple strategy of delaying wins out over animal tactics.

Nevertheless, putting off the bud break can’t be the only remedy for defoliation. Insects that consume the leaves are numerous, particularly in spring, when the tree needs sugars to build new tissues, such as wood. This is a particularly fragile period. And so, faced with a wide variety of attackers, Quercus has an arsenal of responses. For example, he changes the nitrogen concentration in his cells. Caterpillars and other defoliators value nitrogen highly – it stimulates their growth and their fertility. This is why their droppings are so full of nitrogen. They consume so much they can’t absorb it all – in high concentrations it can end up being lethal – so some is cast off. But in summer, when all the leaves are formed, new molecules appear in Quercus’s phloem sap, made of unappealing low-nitrogen amino acids such as glutamic acid, aspartic acid and alanine.

While Quercus is undergoing the first attacks, he asks his chloroplasts to produce new molecules: tannins. It’s a race against time, because the longer he waits to make these substances, the more his foliage disappears and thus the fewer molecules he can produce. Quercus – rooted, fixed in his forest with no possibility of escape – plays a high-stakes game. The tree carries out a kind of risk assessment and prepares his immune system.

Over the course of weeks and then months, tannins accumulate in the leaves, which harden and lose their water and proteins. Tannins are water-soluble polyphenols, complex molecules that give plants the major part of their tastes and colours, but above all, they provide essential protection for Quercus. Like molecular Swiss army knives, they are, in particular, hard to digest, and insects that consume them suffer effects such as slower growth, or even intoxication. Tannins are the tree’s first rampart; they could almost be likened to toxins. In response to any attack, each of Quercus’s leaves produces tannins, which are sent to all the tree’s tissues from roots to crown. They accumulate in molecular rubbish bins inside each cell: a closed pocket, the vacuole, which is never emptied. By pumping his cells full of tannins, Quercus gradually makes them unappetising to insects.

The panoply of tannins is vast. Some are too light to inhibit the action of defoliators. Others are so heavy they impede the insects’ digestive enzymes. If the tree is hurt, tannins limit the effects of oxidation on the internal cells that are suddenly in direct contact with oxygen in the air. Too much sun? When you have no sunscreen, it must be replaced with something else, and so the tree creates another category of tannins with a very specific function: flavonoids, which protect the surface of the leaves from heat scorch. Even in autumn, when the leaves fall, tannins enclosed in the vacuoles play an unexpected role. Some of them – the anthocyanins – colour the leaves while the chloroplasts gradually disappear, as though to warn the insects: ‘Leaf full of tannins! Move along – not digestible.’ And it works! Aphids are particularly sensitive to this message and keep their distance.

At a rhythmic and time-honoured pace, unchanged for hundreds of millions of years, the leaves of deciduous trees turn brown, yellow or red in autumn, fall to the ground, and then begin to decompose in spring. Tannins prevent their mechanical decomposition, so after the winter dormancy, the leaves don’t break down without the help of primary decomposers in the leaf litter, such as Nemobius the cricket, who cuts them up into tiny pieces. When Quercus awakens in the spring, the leaves will redistribute all their molecules to the soil, which are then gathered up by Leccinum to be transported to the tree just when he needs them most. This efficient cycle avoids winter losses, because the rain could leach the soil and carry nutrient molecules off to areas that are inaccessible to the trees. So everything is collected in spring, even the tannin building blocks.

But Quercus doesn’t stop there. There are other substances in his chemical armoury; tannins don’t always suffice. He makes alkaloids, derived from amino acids – these never make up more than two per cent of the leaves’ weight, but still radically reduce the leaf’s nutritional value. Other molecules such as terpenes help with the dispersal of odours, whether they be monoterpenes like alpha-pinene or beta-pinene, diterpenes such as phytol, triterpines, carotenes, limonenes or sesquiterpenes, from the family of hydrocarbons. The tree has all these ways to modify the structure of the tissues in order to limit attackers. Also present are essential oils, glucosides, terpenoids, phytoncides, vitamin A and bitter principles. Terpenes and alkaloids are volatile, which can be a definite advantage for Quercus. In short, one parasitic attack is enough to set the chemical factories running in each of Quercus’s leaves, changing their production line to make molecules with very different functions from the formation of basic oak tissues. Chloroplast – kitchen, dining room and hospital in its time – becomes the arms factory that prepares Quercus for the immune battle.

When the leaves begin to be devoured, cells that are attacked transmit little electric shocks whose message is clear. These shocks ionise the air around the leaf, accelerating the transmission of information. The cells that receive them set to work producing the variety of molecules mentioned above. Some reduce the leaves’ digestibility, others their nutritional value, and still others inhibit the growth and fertility of the insects that eat them.

But now a new problem arises for Quercus: when a group of leaves is attacked, it’s in the tree’s interest to develop defences everywhere the risk exists. This means he must warn all his foliage, because a defoliating insect is rarely alone. However, Quercus is a plant. He doesn’t have a nervous system that allows him to circulate information, as animals do. The electric shocks can only inform neighbouring cells. The first solution is to transmit informative molecules via phloem sap to the other branches and all the way to his roots. We now know that this information flows to the roots and then onward to the mycelia, and can sometimes be found in the sap of neighbouring trees.

When one tree is attacked, the response of the forest becomes collective. If the neighbouring trees also start making defence molecules, the population of defoliating insects would soon face a food shortage. Standing together is a successful immune response. But the speed of circulation of all these fluids isn’t fast enough. This is a lightning war. It might take a few hours, or even one or two days before all Quercus’s tissues have been warned, but some insects operate en masse, and quickly.

So, he employs a second strategy, one that’s rather costly, but which will pay off in the end. Quercus makes volatile terpenes and alkaloids, sent out through his stomata and dispersed into the air. He hands over the alert message to the air and the wind. The neighbouring leaves receive the information in just a few minutes, and their sensory receptors identify the problem and initiate the appropriate reaction. The power of these methods is such that, if Quercus experiences an attack on a branch at the time of his bud break, he’s able – if there are already a few whole leaves in the affected area – to make these molecules again elsewhere on the tree, and rapidly transmit the information to neighbouring branches. Step by step, the whole tree is warned of the danger. These neighbouring branches can then slow their budding to avoid suffering the same attack. As an additional benefit, neighbouring trees are also warned in good time.

Nature has bestowed Quercus with chemical weapons powerful enough that defoliating insects and primary consumers – wood-eating xylophages – can’t imperil the future of the trees. Their impact is limited to just two per cent of all wood production in a typical year, even when we observe up to ten per cent fewer leaves on a tree. Only rarely are Tortrix or other caterpillar populations so high that oaks are more significantly defoliated and forced to rebuild their foliage.

Quercus is weakened, but the Tortrix population would not have risked killing their support system. Instead, a balance was instated. Quercus was not consumed in his entirety, and anyway, he has stronger neighbours that would ensure the oak grove’s continuity if he did die. Any tree that dies as a result of phytophagous insects redistributes its minerals to neighbouring trees, whose growth is thereby stimulated. The sacrifice of one benefits the rest.

Without knowing it, the vertebrate fauna that pass by or live among the trees during the growing season are bathed in the trees’ volatile defence molecules. Some molecules might affect their senses, they’re that powerful – terpenes, for example, which are nothing other than hydrocarbons. But their effects are greatly diminished by dilution in the large volume of air. Conversely, other molecules can impart extraordinary qualities. Phytoncides, for example, produced continuously by the trees, limit the development of bacteria and saprophagous fungi, which alter leaves and wood. And because they are volatile, phytoncides allow the tree to communicate with its neighbours or between distant branches. Mainly produced in the middle of the day, these phytoncides play an unexpected role by stimulating production of natural killer (NK) cells. These NK cells are part of the immune system in mammals and protect human beings against a number of illnesses.

Meanwhile, the various attacks on leaves cause the production of electrical micro discharges. These are also released into the air, charging it with mainly negative ions. The ions stimulate the growth of plant cells, and thus the repair of affected tissues, while also participating in the transmission of warning messages. In winter or during the full moon, the tree produces mainly positive ions, which are less beneficial. But from spring to autumn, negative ions predominate widely. We humans are sensitive to these. Contact with negative ions, even in the air, decreases our cortisol production, a hormone that contributes to stress, anxiety and depression. For humans, less cortisol also means a decreased heart rate and, consequently, lower cardiovascular risk.

These days, we sometimes notice trees experiencing difficulties in the forest. There are unmistakable signs: loss of foliage from the ends of their branches, or limbs dying in the canopy. I have sometimes come across hikers looking sadly at defoliated trees. They may glimpse insects that seem to be attacking the wood and leaves and worry that the tree will suffer, or die. Sometimes they’re even shocked that foresters are doing nothing to prevent these insects from weakening the forest.

Aside from using chemical products that are so harmful both for nature and our own health, what can be done? The forest has a different value system to human-kind. Death is part of woodland life. It is continuous, and its causes are often invisible, but it is an important part of the healthy functioning of the ecosystem. And for those beings who endure, nature has other strategies. Being subject to constant attacks is what has forced Quercus to learn to defend himself and develop immunity. Paradoxically, if we isolated Quercus so as to save him from each year’s attacks, he would probably lose his well-honed and incredibly efficient immune power. And because he has developed several strategies, most of which are chemical and dynamic, he shares his strength with the whole forest community. Leaving nature to its course is the best solution for everyone. And we humans are the first to benefit.

NEUROTERUS, THE WASP, 1850

In which we learn that Quercus is no longer an adolescent, and that, since turning sixty, he has begun to reproduce. But his reproduction coincides with that of a wasp, Neuroterus. She persuades Quercus to help her, and we observe Neuroterus growing peacefully, protected and fed by the oak. We discover that this wasp has adapted to produce two generations per year, one sexual, or gamic, and the other agamic – without using the semen of a single male. But is the tree being deceived by the insect?

The year is 1850.

Neuroterus has just emerged from the ground where she spent the whole winter. The first rays of sun have begun to warm the atmosphere and the days have started to lengthen. From this moment on, everything speeds up. The alarm sounds: Neuroterus must find a partner as quickly as possible.

This gall wasp of the family Cynipidae is a completely black insect called Neuroterus quercusbaccarum, the common spangle gall wasp. It is short at two-and-a-half-millimetres long but fairly wide – if you weren’t paying close attention, it would almost look like a fly. Neuroterus is one of the tiny insects that buzzes in the underbrush that we mistakenly associate with gnats. She begins her imago, or adult, life with just one goal: to procreate. In these first days of April, spring is already well on its way and she must hurry; it’s already late in the season.

The wasp takes flight, meets a male, and mates with him. Next comes the search for a host plant, an oak. There’s no shortage of them here. Neuroterus flies up to the canopy and finds what she’s looking for: a bud that’s still tightly closed.

The weather conditions this April are perfect for starting the costly production of fruit. Quercus may have learned to take his time to avoid Tortrix, but he began preparing to fruit even before the bud break. The stored starch and sugars begin to rise towards his crown even as he could only pray there would be no frost during the formation of the catkins.

This year he is lucky – no frosts come. Quercus has the task of simultaneously making yellow catkins – spindly and fili-form, carrying male flowers – and solitary red female flowers, nestled in the leaf axils and covered by tomentose scales like a protective quilt, which we call an involucre. These flowers are small, and the grains of pollen on the male catkins are minuscule and very light, allowing them to be carried immediately by the wind to join the female flowers.

Occasionally, some insects transport Quercus’s pollens. But this phenomenon is rare, because it’s usually the sweet nectar produced by the flowers that attracts insect pollinators, and Quercus doesn’t really produce any. This is a result of evolution: sweet nectar is costly in energy; the oak trusts the wind far more than any insect or animal.

Fertilised, Neuroterus arrives near one of Quercus’s buds, which have just opened. The wasp can already detect the first springtime organs. Beginnings of leaves and the hint of reproductive catkins. This is exactly what she needs. She settles on a male catkin, hanging long and loose.

* * *

Since turning sixty, Quercus has been reproducing. He does this in certain years according to his own cycle, influenced by alternating spring temperatures which are sometimes mild, sometimes freezing. His sexual maturity may seem late, but it’s normal for his species. Over the years, Quercus has learned to make acorns in tune with meteorological conditions to limit the risks of them being eaten immediately. Apodemus the wood mouse and his descendants remain one of Quercus’s worst fears – or at least, one of the most significant threats to his own descendants, along with a few bigger species such as wild boar. Animals that can harm his catkins are less of a problem; they are generally low in numbers and so small they don’t do that much damage. This tiny wasp is one of them.

* * *

Neuroterus selects the catkin’s stem, brings forth her ovipositor, or laying organ, from under her abdomen and pierces the plant’s still-fragile, hypervascularised stem, ideal for a continuous and unlimited supply of food. She inserts her eggs. Once the operation is over, Neuroterus’s work is done and she heads off deeper into the forest.

After a few weeks, the eggs hatch and their young larvae produce a whole series of proteins and enzymes which have the unfortunate tendency of throwing Quercus off course. They invite the tree to reorient his production of auxin, the growth hormone his tissues need to develop according to the tree’s genetic map, especially during the bud break. Quercus begins to make very hard tissues that form a little green ball around each insect larva to insulate it. The tree doesn’t know he’s being manipulated according to the strategy of Neuroterus’s larvae.

The young Neuroterus slowly emerges from the leaf blade, while the catkin makes the gall or cecidium that will envelop it. This is a sort of very hard plant shell, resembling a green gooseberry, which will ensure ironclad protection against potential predators and external conditions. Her strategy is purely parasitical: above all, she doesn’t want the tissue to die. On the contrary, the tissue must continue living and being fed by the tree, because the growing larva draws resources from the circulating sap. In order to grow more efficiently, Neuroterus requires ever more nutrients but is confronted with a major problem: she’s now enclosed in a gall whose walls are full of seemingly indestructible tannins, isolating her from the oak. How will she get more food, and how will she be able to continue growing and emerge from here? How can she be sure that the protective cocoon, produced by Quercus against his will, doesn’t transform into a prison – or even a tomb? The larva’s strategy is to send out a new enzyme, phenoloxidase, to the leaf blade that simulates new growth hormones. The tree, deceived by the insect, now makes a well-differentiated layer of nutrient-rich tissue around the larva, while reinforcing the tannic protection towards the cuticle of the gall. Quercus works for Neuroterus. The situation is perfect for both her growth and her protection. Quercus doesn’t even feel the presence of the parasite, especially because there are so few of them. He’s been duped into believing he is simply responding to a request for nutrients – a particularly intense one, it’s true – from the catkin. He produces the required sugars without suspecting a thing.

The time then comes for pollination. The winds of May carry off the grains of pollen, only some of which land on the female flowers. But it’s enough. A ray of sun cuts through the underbrush, allowing this seeming dust to be seen all around the oaks. The ovules don’t form until well after the pollen is gathered. The female flower is not fertilised until the beginning of summer, and the acorns form after that. Quercus makes thousands of them; it is now time for the massive reproduction of oaks in our forest. The trees employ the strategy, called ‘masting’, of producing a vast amount of acorns in the same year to disrupt rodents’ reproduction cycles and elude the teeth of future acorneaters. Apodemus and his descendants will pay the price for this glut when they have nothing to eat the following year.

* * *

In the meantime, Neuroterus has a problem. Once pollination has occurred, the host oak no longer needs the male catkins. Since the organ has become useless, Quercus could conceivably abandon it. This would be in his interest for reasons of energy conservation. So Neuroterus sends enzymes at regular intervals to simulate the hormones that keep up the influx of phloem sap. The wasp’s prerogative is to keep maintaining contact, in the form of a seemingly fair – but in fact one-sided – molecular exchange.

Does Quercus have a way of reflecting on this phenomenon? Probably not. Heedless, he continues to provide nutrients to the greedy catkin. Right up until the day when he finally realises the farce has gone on long enough. He no longer needs to support the catkin because he has already released his pollen, and since the growing wasp’s messages don’t correspond to the cycle he’s used to, Quercus abandons the catkin, which falls to the ground along with the gall.

The round green gall lies on the ground among the dead leaves. This is not so bad for the larva – she still has her nutritious tissue, kindly provided by the tree, and stays sheltered inside until it’s time to emerge. The larva begins her transformation. The new wasp forms in just a few days, and then the insect pierces a hole and emerges into the month of July.

* * *

Now she faces a new problem: the life cycle of the species is such that there are no males at this time of year. But nature has given Neuroterus a considerable advantage: parthenogenesis. While the first generation in spring is called ‘sexual’, or gamic, requiring males and females, this later one is called ‘agamic’. The second generation skips the step of mating and goes directly in search of a site to place its non-fertilised eggs. There are no more catkins this season, so the wasp will lay eggs on an exposed root, where the larva-to-come will generate the same chain reactions, prompting the formation of a gall that, this time, will offer protection against predators and the coming winter. Quercus will be spared this, because his root system plunges quickly into the ground. But a neighbouring oak will house a few unfertilised eggs from our young wasp in the bark of its roots. This is how Neuroterus prepares the next generation, which will produce both males and females the following March, or in April if they are slow to emerge.

* * *

Despite the interference of the parasite, Quercus has been able to reproduce without much difficulty. But this episode illustrates what a complex game pollination is for the trees, just as for all floricultural species. Each flower has its procession of pollinating insects, or its strategy, like Quercus’s, of relying on the wind. Each pollinator responds to a precise cycle, involving the use of clearly defined habitats. For example, many wildflowers are pollinated by small solitary bees that build nests in the sand, in full sun. The slope at the edge of the sandy path leading to Quercus is full of them, and we can see the little tunnels they’ve dug. For flowers of herbaceous plants, just like many trees, these wild insects are essential: there’s no fertilisation without them. It’s essential these insects find an array of different living environments to allow them to complete their cycle, such as these flowering areas and bare sandy slopes.

The larva of some of these pollinators need sugar from flower nectar to grow, but prey – other insects – also give them the protein necessary for their growth. And among the prey we find … cynipid wasps, like Neuroterus. In this way, the gall wasp’s manipulation of Quercus is kept in check. The circle is complete.

HOMO, 1860

In which we learn of the paradoxical nature of forestry. On the one hand, forests are flourishing because growing practices are changing, and, on the other, certain forests are in decline because the need for wood is so great. This situation evokes strong emotions for some; awareness of an ecological crisis is growing. Measures are put in place that will finally allow for forest recovery, but this will take decades. During this time, Quercus begins to resemble an adult oak, although he is still technically an adolescent.

Quercus is approaching eighty years old. The year is 1860.

In 1856, all grazing in the forest is halted. This will radically transform the physiognomy of the underbrush; now, the forest, which looks like a wooded heath, will no longer have to withstand the permanent pressure of flocks. No more incessant nibbling at seedlings trying to extricate themselves from brambles. The Rambouillet heathlands will gradually give way to the forest we know today, and the underbrush will finally grow more dense.

Not all woodlands are as fortunate. French forests as a whole continue to recede, because elsewhere, wood is still being harvested, the overall agricultural area is growing larger, and cities are gaining ground over the countryside. In 1857, when Quercus is twenty-five metres tall, the forested area in France is at its lowest historical point, covering only thirteen per cent of the country. Before the Revolution, when Quercus had just extricated himself from the bramble, the inhabitants of Paris used wood to heat their homes at a rate of approximately one million cubic metres of firewood per year. And demand was only growing, as new arrivals flooded in from the countryside. The construction of a ship required between three and four thousand adult oaks, not counting the tall fir trees used to build the masts.

* * *

During the Revolution, the people wish to abolish the nobility’s system of feudal land ownership. The forests are redistributed between new private owners. Forest protection services face many difficulties. Royal hunting captaincies are also eliminated. Foresters are forced to turn a blind eye to poaching, which does at least help reduce wild game populations and allow a few stumps to produce new offshoots and plants to grow, because there are fewer herbivores in the forest. But the forest is barely hanging on.

Plundering intensifies. Politicians propose laws and ordinances that contradict each other, the primary goal of which is to decrease the supremacy of a higher social caste and return the forest to the people. If a forester attempts to step between the looters and the trees for which he feels responsible, he’s putting himself at risk. One forester is killed by commoners in a mad frenzy. The latter are judged and hanged. You don’t mess with trees.

* * *

A new revolution begins, this one industrial. The demand for wood spirals out of control. Paris goes as far as the Morvan, nearly three hundred kilometres away, for its firewood. The growing city is an ogre devouring all the forests for hundreds of kilometres around. The rivers are recalibrated to transport thousands of logs to big cities and ports. In their frenetic consumption of wood, human beings have created a problem that will become extremely significant in the next century: carbon emissions. But, could this be an opportunity for the forest? Quercus feels the imperceptible increase of carbon in the air he breathes. Year after year, he receives this offering, and at first it’s a blessing. He can grow more quickly, eating up carbon atoms avidly – but what will the long term impact be? For the moment, no one has realised its significance. Quercus simply takes the offering for what it is.

Meanwhile, with the price of wood on the rise, people begin to speculate on it and the new forest owners take advantage of the boon to sell their resources. However, some are becoming aware of an emerging paradox: deforestation is dragging the economy into a dead end. Wood may not be as renewable as was once thought. The establishment of forest reserves is proposed and the first forest code of 1827 is announced, aiming to restore woodlands to their former glory. But the forested area in France continues to diminish for another thirty years, right up until 1837, when it reaches that ominous figure of thirteen per cent. Once again, the future of our forests is at stake.

This time, the alarm sounds even more loudly. The wooded landscapes we know today are a product of this social outcry in the mid-19th century. Our forests become the subject of great philosophical debates tackling the place of industrialisation in our society, the abandonment of the countryside, and the expansion of cities. Are we losing touch with nature? Great thinkers of the Enlightenment become involved. Jean Jacques Rousseau appoints himself ambassador of natural forests; he has always considered them to be privileged places, conducive to the meditation he practices. He believes forests are the only way to escape the woes of the world; only in forests can we feel true happiness and cultivate the beauty in everything. He goes so far as to say that, by contrast, immersing himself in the political, economic and industrial issues of the time was erasing his best ideas. What a trailblazer!

Rousseau’s sensitive, romantic vision upends our way of seeing the forest. From the Romantic movement on, the idea was born that interfering with the forest could potentially lead to a chain of hydrological, climatic (already!) and geological catastrophes. Not only in the forests, but in all our landscapes. People begin to notice that the forest plays an essential role in purifying the air, although they believe it is through trees transforming miasma, dust and noxious gases into pure air. Such incredible clairvoyance!

The Age of Enlightenment and the period that followed give rise to the first signs of ecological thinking. From the beginning of the 19th century, thinkers begin to argue that deforestation must cease and planting begin. France must be reforested, they say. Severe floods in 1840 and 1856 prove them right; the trees are no longer there to slow the flow of water.

Passions run high. Disagreements over the ecological analysis of observed disturbances in nature continue to provoke long debates, even at the National Assembly. Objective research in the field must be conducted. Numbers are demanded. This is when science begins to show an interest in the forest. Techniques of forest management are discussed. Reforestation, in the mountains for example, is considered as a way of stabilising the soil and avoiding landslides.

Finally, a department to oversee forest management is proposed, with staff trained in sylviculture – or ways of efficiently cultivating forests. The Forest Code must be enforced. This is how, in 1829, when the forest is at its lowest point, the first forestry school is created, along with the prestigious Ministry of Water and Forests.

* * *

As time passes, the activity in our forest changes. Most agricultural intrusions have ended. Quercus’s environment is going to be radically altered. This forest was previously managed as a space from which a maximum of resources could be gathered, to feed humans and animals. Now, abandoned, the marsh returns little by little to its natural functions. Plant debris accumulates and blocks the few trenches that had been dug in an attempt to drain and cultivate the land. However, successive fires – accidents provoked by growers next to the forest attempting to regenerate their pastures with a slash-and-burn technique – don’t make it easy for typical wetland plant life to reestablish itself, and bracken takes hold instead. This plant is considered a pyrophyte: it thrives in areas where fires have blazed and cleared the land, leaving space for it to take root. But bracken makes it difficult for other plants to establish themselves, even pioneering trees such as birch.

Alongside the wetlands, the heaths grow back, because they no longer have to support grazing livestock. Large herbivores still come occasionally, but never stay long, and their impact on plant life remains negligible. The forest goes on, peacefully, because now the trees can produce seeds and many of them will survive to germinate in safety.

New silviculturists take over our forest, with two main goals: for the forest to grow, and for the wooded heathlands to give way to stands of tall trees and coppices. The latter can continue to offer firewood to neighbouring inhabitants. Quercus, the strongest of his kind, is selected, and the other oaks, his siblings, are cut down because of their smaller size. These trees were too tightly packed together, and wouldn’t have been able to continue to grow without their adult survival being compromised.

Quercus is now twenty-five metres tall. Taking his life expectancy into account, he’s still an adolescent. But he’s been reproducing for the past twenty years now. Because of the crowding from other saplings when he was small, Quercus doesn’t have low branches, aside from those that reach northward at a height of just six metres. The harvesting of his neighbours results in a new opening towards the sky, which will help his higher branches. The architecture of the future great oak, the one I know today, is being finalised. Only one neighbour remains to cast a little shade for his full adult development – the parent tree.

CANIS, THE WOLF, 1869

In which we observe, and are powerless to stop, humans interfering with natural cycles that have taken millions of years to establish. We understand that the imbalances in nature brought about by the major event described here will never truly be put right. We observe the disappearance of the super-predator of our forests, and the consequences of its loss.

The year is 1869.

On this autumn day, an almost-electric atmosphere reigns, heavy and humid. The tension is palpable throughout the forest. An animal – a predator – has become prey.

* * *

The fog hasn’t lifted. It’s so dark, it’s impossible to see further than a few metres ahead. A stench of decomposing plant matter burns the nostrils, accompanied by damp wafts from the underbrush, where the scent of fungi in leaf litter predominates. Everything reeks of decomposition. The dampness penetrates every living animal in the forest – it’s impossible to get warm, except by running. The forest is silent: not a murmur, not a song nor call of a bird, not even a sound in the tree canopy, which seems to stand immobile, in the absence of wind. Even the air is still. From far off come the sounds of barking. The dogs follow a scent they first picked up at dawn, and now they are excited. The people with the dogs carry stakes and guns. They’ve dreamed of this moment. They can feel victory approaching, the end of the long, long chase. Running through the woods, they approach Quercus. Their prey – intelligent, desperate – has led them into the neighbouring marsh, in the hopes that they’ll lose his scent. But this time, it will be in vain.

An animal arrives, in distress, tongue lolling. The chase has been on since daybreak. He stops at the foot of the parent tree, turns and pricks up his ears. Canis is on high alert. He knows humans despise him, the way we’ve despised all members of his species for centuries. No other animal in the forest is more resilient.

The abandonment of certain pastoral and agricultural activities in forest plots and marshes has allowed more natural vegetation to grow, including a few small bushes. The wolf, Canis lupus, can more easily hide and watch for prey without being seen, as though he has an invisibility cloak. But today, Canis is the last of his species in this large forest. All his peers have been killed; the hatred people feel for his kind is so intense. And all because of a misinterpretation, a lack of understanding.

* * *

On this autumn day in 1869, Canis is tracked, as all his peers were before him. He liked rooting around in the underbrush, which helped to regulate the rodent population, including the descendants of Apodemus, who could otherwise affect the forest’s regeneration. He especially liked chasing wild boar, deer and stags. His role as a super-predator helped with the forest’s recovery. Quercus benefited from the wolf’s presence, because large herbivores were forever anxious, alert to Canis. The wolf has this power: through his mere presence, deer have evolved to be more mobile, because they’re in a state of constant fear. The howls of the packs are a challenge, just as much as an invitation to the hunt; the deer know perfectly well how to interpret them. Over the years, Canis and his pack have tracked down several deer and wild boar, leaving their carcasses scattered, providing food for numerous other opportunistic organisms.

Canis’s pack has long since disappeared. But even alone, he provokes fear in the other mammals of the forest. Faced with predation, large herds of deer scatter into smaller groups to reduce the risk of being spotted and eaten. Animals rarely stay for long in one area of the forest, for fear of leaving scents that would allow the canine to track them to their dens.

Now, Canis is on the alert, his senses keen, ears pricked up. He hears dogs barking – they’re getting closer. He knows it’s him they’re after, and his stress level rises sharply. The gamekeeper killed the other members of his family: his parents, brothers and sisters. He must run. The advantage he has over the dogs is his endurance. Wolves can push their prey in a direction of their choice over many kilometres, to the point of exhaustion. By continuing at a steady pace, he should manage to outrun them.

* * *

But why this human contempt? Wolves naturally hunt in packs and avoid peopled territory, though humans must still maintain its borders. For a wolf, marking the edges of territory is essential. This is their language. If you want to make them understand they’re not to cross certain borders, it’s imperative to use this signal.

The absence of such markings around human dwellings leads wolves to conclude that domesticated animals, living free-range, are potential food. Cases of predation are rare, since domestic animals are usually put inside at night – but they have happened. And to the wolves’ great misfortune, people have begun to hunt them in retaliation.

Sometimes, wolves are also accused of voluntary homicide – once again, a case of misunderstanding. Wolves don’t normally attack humans, or eat human flesh. But over the centuries, wars between human beings have sometimes been so violent and relentless that bodies were left to decompose on battlefields, where, out of opportunism, some wolves ate a little of the flesh and unfortunately acquired a taste for it. A few packs began to pose a problem for humans. Once again, these cases were rare, and ended with the death of the wolves involved. Then some wolves contracted rabies. All it took was a few cases to end the lupine era.

Humans know how to embellish history to serve their interests. In wolves, it was convenient to find a scapegoat for nature’s ills. Homo’s taste for comfort led them to abandon ancestral nomadism in favour of sedentary herding and farming. Fine! But then they needed to master their new environment and eliminate risks to their livestock. After all, humans prefer to remain the only super-predator. They don’t like competition.

For all these reasons, lords, and then kings, have declared war on the wolf, as though their supposed divine right to rule over humankind extends to deciding which other species have a rightful place in nature. The right to life, the power of death over the fruits of millions of years of biological evolution. For centuries, wolves have been persecuted. Now, they will be exterminated. The Louveterie royal, a special wolf catcher corps, is formed for this express purpose.

Canis starts running again. The dogs and men have come dangerously close. What he doesn’t know is that two other groups are waiting further ahead – this pack is pushing him into a trap. After passing under Quercus’s crown, he makes it just three kilometres north before he’s cornered by the other groups. There’s no way out. Alone against so much energy deployed to destroy him, Canis has no chance.

In 1869, the last wolf in the Rambouillet forest is killed by the rural guard of Poigny.

This is the era when we begin, for the first time in centuries, to observe the gradual recovery of France’s forests. In this new forest, however, Quercus and all the other trees can no longer count on the help of the super-predator, the wolf. The wolf’s disappearance may seem incidental, but the trees no longer have Canis to fight the daily grazing of their seedlings: the carnivore who eats the herbivores who eats the plants. Now they are solely and entirely dependent on Homo. But can humans really replace the wolf? Can they fend off the species that impact regeneration, such as the descendants of Apodemus? History shows that this part of the cycle will be left to Mother Nature alone. Homo always assumes she will be able to compensate for our actions, fortunate or unfortunate. But the relationship between herbivores and forest development will never be the same again.

Exactly one hundred and fifty years later, in 2019, a wolf will be spotted arriving from the east, after crossing the Île-de-France to reach Normandy. A century and a half after Canis’s extermination, members of his kind, descended from the Italian population, will once more pass through Rambouillet.

SILVA, THE FOREST, 1871

In which a landmark event occurs for Quercus and Silva, the forest. An event which is experienced as a drama, but is also an opportunity for the trees. The death of the parent tree comes as a second birth for Quercus and his neighbours. And we discover that all trees are autobiographical, as their stumps will reveal.

The year is 1871.

A few years after the death of the historical super-predator of Rambouillet, an ominous signal circulates in the air: somewhere in the forest, someone is not doing well.

The forest, Silva, this collective being, registers that terminal molecules are being emitted by a suffering tree. The other oaks in the area receive the information, as well as other species of trees capable of detecting distress molecules resembling their own. Insects too perceive these signals. These circulate through the air and, for some, through the mycelium of Leccinum quercinum which is connected to Quercus. The quantity of terpenes and alkaloids suggests that multiple oaks are fighting for their survival at the same time, which is a rather rare phenomenon. Unless … Yes, that’s it, the message is clear: the parent tree, majestic and imposing as she is, is in her final moments. The whole forest is alerted.

Over the past few years, the parent tree, empress of the forest, has begun to show signs of weakness. She has sometimes failed to transport raw sap all the way to the crown, and channels have been dug by insects from the surface of the bark towards the heart of the tree. The tree usually has the ability to seal these up fairly quickly, but only when she has the resources. If she is too weak, air can circulate all the way into her tissues, and that is what has happened. Insignificant to begin with, as air is let into the vessels, small weaknesses lead to others. And then still more. The air has created pockets, blocking the tree’s sap so that it’s no longer sucked towards the crown through evapotranspiration. The tree has put all her energy into trying to seal the few vessels that were feeding tissues and branches already in decline. There were too few leaves left to ensure the necessary evaporation for the call for nutrients at the top of the tree, and capillary action was not enough to pull water loaded with trace elements towards the remaining leaves. Gradually, the oak abandoned one element – a twig, a branch – then another.

A tree is such an exceptional being that each organ – each leaf, for example – no matter where it is on the tree, can provide all photochemical functions. Thus, the tree doesn’t lose a vital organ when it detaches a branch – the others are capable of seamlessly taking over all functions. But for a few years now, some of the boughs in the higher branches have begun to dry out, and the foliage is thinning. The parent tree has more and more difficulty conserving enough foliage to complete her cycles. This year, a large portion of her crown wasn’t able to extract the necessary fluids for her to make it through the spring. Only a few branches survived. Is it possible to keep pushing back the inevitable?

Then, in a final gesture of transmission towards the forest, the ailing tree releases a multitude of fruits, far more than her healthy neighbours could produce in the same year, in the hope they will carry on her lineage – if, indeed, a tree feels that sort of thing. This desperate gesture has one immediate consequence: it depletes the tree of her last reserves of lipids, starch and sugars she would need to set off a new bud break the following spring. This grand gesture of reproductive fireworks is fatal: suicide by acorns. During this time, more and more pockets of air enter the sap. By placing all bets on a final round of reproduction, the parent tree, the empress of this forest, is caught in a paroxysm that signals the end of a forest legend. After winter, the parent tree will dry up for good.

* * *

At this point in our story, while industry, railways and cities are being developed, each piece of wood is too precious to be abandoned. Humans do not even wait for the tree to die completely before arriving with axes and saws to cut her down. Her fall makes the ground shake for Quercus as never before. His foliage trembles, as much from the violent impact of the parent tree hitting the ground as from the gust of air caused by the fall. The parent trunk splinters. As after the fall of any tree, whether caused by the actions of humans or of nature, the forest becomes silent. Only the eerie sound of the wind in the leaves reveals the living nature of the trees still standing, whose bond with their parent has just been broken. Not a single bird dares to move or sing.

The scent of freshly cut wood fills the air, charged with tannins – a cocktail of delicate, sweet aromas characteristic of oak wood; coconut, dried fruit and vanilla. Collectively, the forest population fears a consequence that would mean a large-scale disturbance threatening their environment and survival. Everyone and everything is on alert. But nothing comes.

The bare stump reveals the history of the tree and her environment. Each year, at the time of the bud break, the tree builds large channels to carry the raw sap to the secondary xylem in the sapwood, and much narrower channels for the descent of the phloem sap to the phloem. These two layers of cells make up one line that goes from lighter wood to wood that’s darker and tighter – we call this a growth ring. Studying them allows us to decipher the tree’s history. Tight rings on one side in a section that’s almost oval indicate that the wood was compressed, so the tree began to lean in that direction. On the other side, fibres then developed large reaction cells in response to the trunk leaning towards the ground, forming tension wood to pull the tree towards vertical.

If the rings are tight everywhere, we know there were periods of slowed growth, probably because she was too close to her neighbours. Competition for access to light restricted her crown, which had to stretch to find space between several tightly-packed trees. So the trunk had to grow more slowly. A series of much larger rings usually means a thinning out, neighbouring trees being harvested, allowing this one to spread out. An injury leads to the formation of tissue – here, isolating the injury by covering the affected tissue with cells that are harder but also smaller and rich in lignin, that very solid tannin molecule, forming narrower rings. Here again, an injury in the bark will leave an indelible trace in the underlying ring and the ones that follow – the tree will not be able to erase it – forming an incision in the wood that can be isolated and integrated into the heart of the tree.

In this way, all trees are constantly writing their memoirs. As autobiographers, they record the difficult moments, physical or climatic events, and periods of abundance or scarcity. They unconsciously forge in each cell reaction not only the constraints they experience during their development, but also the opportunities and changes that offer the trees new space and nourishing light. And so, year after year, the parent tree has integrated her story into her architecture. Ever since the day that he, Quercus, and all the other trees on our green and blue planet took root, their story was being written inside them. By contrast, to record our memories, we humans must use tools, such as the paper we make – sacrificing trees in the process.

If the loggers who cut down the parent tree had read her rings, what would they have discovered? What secrets had she guarded inside her heart? What stories would have been revealed? The parent tree, likely born hundreds of years before, had lived through times of famine, sickness and war; may have lived through the Crusades, the Hundred Years War and many others besides; and had seen the gradual disappearance of the forests. This tree was probably born when the forested area was twice as large as on the day she died. And she was descended from another oak before her, the parent of the parent tree, which had perhaps grown in a heathland landscape, alone, deprived of others of its kind, while its very essence was to be gregarious, to live in a dense and diverse forest community. This tree developed in a world in which utilitarian functions were imposed on her by humans: producing fruits – the acorns that fed the livestock – and offering shade on hot days, especially to riders. She bequeathed to Silva an abundance of offspring ready to forge a forest much like the one we know today: rich with multiple strata of vegetation, from tall trees to a dense underbrush. And now the parent tree, that has come through the ages, is dead. Her stump will allow us to conserve the memory of the event for a few decades, and then the stump too will disappear. The fact that all this is part of the natural cycle of life does not lessen the shock for Silva.

Disturbances in the forest elicit reactions. Above all, this death signifies an opportunity for saplings to enjoy the light that floods into the space left by the parent tree. Light is the source of woody promise. The young trees rise up in search of more.

Next comes the race for the skies. Because he already had help from various sources as a young tree, Quercus is one step ahead, and takes full advantage. A short branch he had begun to make, four metres up, was on the parent tree side. The direct light now enhances its growth, and he can develop further, at the expense of the younger trees which will eventually die off in his shade. Quercus’s growth will accelerate so much, he will soon become one of the dominant trees. And just in time! Because a neighbouring tree of another species was, like him, just waiting for this shaft of light.

FAGUS, THE BEECH TREE, 1872

In which we meet Fagus, another opportunistic but patient tree, who takes advantage of the opening left by the parent tree to grow alongside Quercus. We learn that this tree has capacities that allow it to dominate. And we understand that the fate of each tree is inevitably linked to that of its neighbours. We see that, in the end, for a tree in the forest, growing taller means growing wherever others will allow.

The year is 1872.

The death of a large oak causes considerable upheaval in the forest. The sudden opening in the canopy brings a significant influx of light. A few birch trees have begun to grow in the shaft. This is not surprising – the birch is a pioneer tree, whose seeds are so numerous and light that the wind carries and scatters them throughout the forest. The young birches try their luck, germinating at the slightest chance. In habitats that have always been open, birch trees prepare the ground for others – it takes time for forest humus to be made, for species such as Nemobius or Leccinum to arrive, and the birch leaves help by forming a carpet thick enough for the whole cycle of decomposition of organic matter to be established.

The pioneers are followed by partial-shade species, and Quercus is among them. In spite of his majesty, he does not get the last word. Only a few species belong to the final stage of the forest’s establishment. The beech, Fagus sylvatica, is one. A large beech had produced beech nuts, which were, like the acorns, scattered by animals. Remaining at shrub stage with little light, Fagus had been waiting her turn in the shelter of the parent tree for years, just a few metres away from Quercus.

Her very dense foliage allowed her to absorb the photons necessary for her survival when she was young, even though she stood in the shade. Mycorrhizal connections with a nearby adult beech had brought her some nutrient subsidies, enough to keep her alive for several years. Fagus is patient – it’s in her DNA. Compared to birch trees, she grows very slowly, but she knows how to wait for the opportune moment. She’s only six metres tall and very thin, but she has branches every fifty centimetres starting from the ground.

Fagus could have been gobbled up by deer, but her leaves full of tannins are unappetising. Still, in lean times, she is vulnerable. While Canis was still alive, he limited the action of herbivores, but since then, all bend to the Master Deer when he’s hungry. When the opportunity presents itself, it’s time to spring into action; Fagus has to move fast, to climb higher at all costs, both to escape the reach of the herbivores and to catch the rays of light, at the expense of neighbouring trees, including Quercus. After all, in the forest, the next opportunity might not come along for a century.

In this part of the forest, the environment is well-suited to beech trees. This large valley is oriented east–west, so it opens towards the dominant winds which bring abundant rains. The trees’ capacity to pump water and then release some into the air via their leaves contributes both to producing clouds, and to attracting them. Rain-filled clouds are drawn from the ocean further west, as though atmospheric water sought out contact with the water evaporated by plants. Nearly seven hundred millimetres of rain falls here per year, which is perfect for Fagus and suits Quercus too, even though he is less demanding. Our beech would drink even more water, but this quantity suffices. The neighbouring marsh also produces atmospheric moisture, which the leaves of the beech are able to partly absorb. Living in fog suits her very well. The evaporated water from the marsh also attracts rain, and so summer storms are a regular event, allowing the trees to avoid the effects of summer drought. Finally, the soil is deep, loaded with nutrient-rich silt, but well-filtered as well, because underground sand drains the forest. This set of conditions offers an ideal situation for the development not only of oaks, but of Fagus.

Beech trees are fairly rare in this forest. Their wood doesn’t have the same technical and chemical qualities as oaks. The beech has smooth bark that protects her from difficult conditions, and wood that is very dense and hard because it’s highly lignified, but it remains sensitive to contact with ambient air. Beech wood is the target of several organisms, particularly fungi. These cause the wood to quickly turn blue when it’s cut in autumn or winter, making it less desirable for construction. Besides, logging is impossible here in winter – humans can’t transport the logs rapidly – and so, in Rambouillet, the beech is used for nothing but firewood and the production of charcoal. For these reasons, humans have favoured oaks, even if the ecological conditions of the area are more suited to beech. A few rare, tall beech trees are scattered throughout the forest, especially in places where conditions are particularly favourable. Among them is the parent of the seed that became Fagus. And Fagus is not the only one. A few other nearby seedlings are attempting a breakthrough.

* * *

Fagus may grow slowly, but she establishes herself by extending her crown to take up the maximum amount of space and limit competition. By spreading out in this way, her thick foliage limits the capacity of other plant species to develop below her crown. Only a few young beeches, or a few holly plants, will find enough space to grow at her base. Luckily for Quercus, he’s already a few steps ahead. If he was the same size as Fagus, he would have had a real problem.

The race is on. Quercus will triumph, of course – he started well before Fagus. But the upward thrust of his neighbour has a consequence. If he wants to win, our oak must now focus on the branches of his crown, right below the uppermost foliage. In this way, Fagus effectively helps to prune Quercus’s trunk – not right away, but over time. The fate of the two trees is intertwined: Quercus must maintain his supremacy over the beech in terms of height, or else the ensuing skirmish could tip things in the beech’s favour. Their communal destiny is written.

* * *

When I look at the trees today, I can guess their shared history. The adventure ends with Fagus in a full spread. A few sparser branches stretch in the direction of the oak, but her crown is mostly even, and the branches reach out nearly ten metres from the trunk. Quercus, for his part, has continued to grow taller. He has had to take other neighbours into account, but he’s found his place, and his crown stands a little taller than the rest of the canopy. Below, Fagus’s presence casts a very dark shadow onto the underbrush and Quercus’s lower branches. The day will come when our oak will have to abandon them.

QUERCUS, 1872

In which we discover that Quercus’s nature is ambitious, but also shy. We understand the full complexity of the life of a tree, made up of independent branches all linked to each other, with light defining the architecture of the whole. We grasp that, despite the intra-and interspecies competition, diplomacy is also key for Quercus and his neighbours.

The year is still 1872.

Let’s return for a moment to Quercus’s architecture. When an opening forms in the canopy, he develops a branch or some leaves directly from the trunk. The bark contains a few rare photosynthetic cells that make up the chlorenchyma. If a neighbouring tree dies and light hits his trunk, the tree detects it and develops branches at that level. These epicormic sprouts divert some of the goods from the circulation of phloem sap just behind the bark. They often end up dying because they’re not profitable enough for the tree. But at other times they remain and, when they become too numerous, they give rise to crown dieback – their growth in these cases has become too profitable for the tree.

It’s true that, on occasion, trees growing in direct light show signs of weakness at the top. The crowns dry out because the tree stops feeding them with raw sap, which may actually be the result of an abundance of direct sunlight. Even with the protection of tannins, the tissues struggle in intense heat. The temperature of the sap beneath the bark rises, the leaves lose more water than they’re able to absorb, and the photosynthesis machine wears out. The tissues are abandoned.

But is the tree dying? Not necessarily. Many trees will respond by developing epicormic sprouts lower down along the trunk. As long as these new branches catch the light, they can help with photosynthesis. In this way, the tree develops a new crown that will allow it to shorten the journey of the sap from roots to leaves. The higher parts can then be eliminated, and the tree gets a second wind.

There are obvious examples of this: in England, a tree was photographed during the different stages of its crown dieback. As a mature tree, already wide in diameter, this healthy oak was broken by a violent gust of wind sometime towards the end of the 19th century. The crack appeared above a main branch, a scaffold branch which was crucial in the tree’s history because it picked up the slack from the missing crown. Its foliage allowed it to make all the sugars and other indispensable materials for the development of epicormic sprouts just below the break. More than a century later, this tree is still living, even if it has lost nearly fifteen metres of height.

* * *

Fagus has spreading foliage. On each branch, she develops many leaves. The branches superpose each other, catching almost all the light; very little reaches the ground. This is why saplings or seedlings of other species that need a minimum amount of direct light are unable to survive beneath a beech tree – oaks are one example. The bramble is another, and the one that sheltered Quercus has had to move. Yes, believe it or not, this plant has the ability to shift horizontally through a gradual layering of the stems that touch the ground, to develop new roots and then move in an opportune direction.

Quercus develops in another way. The branches grow by regularly separating, and from a fork in the branch, two or more new branches are born, which themselves end up separating, and so on and so forth up to the crown. Foliage in the shape of a bouquet grows on the last branches, letting light pass through at the edges. And these branches keep a sufficient distance between them to avoid rubbing against each other. Here’s where shyness is a factor. Yes, oaks are shy; they keep their distance from one another to prevent the kind of injury that would initiate the chemical responses we discussed earlier in this book. The oak seems gregarious and likes growing with other trees of its species, but in a stand of oaks, each one has its place. For harmony to flourish, they must avoid acts of aggression. When we look up at their crowns from the ground, we can easily see borders of light around their foliage. What’s surprising is that branches on the same tree can behave the same way, leaving each other room to breathe. Only a few tree species are capable of this – a few dozen species across the world, at most. Additionally, as we’ve seen, Quercus can even slow the chemical and photosynthetic reactions from one branch to the next, for the timing of the bud break, or in response to an attack from defoliating insects.

An oak can be seen as a multiple being, like an individual upon which other almost-independent beings grow. ‘Almost’ because they do still all depend on the same trunk and roots which supply them with water and nutrients. A tree is thus, by definition, a federated being. A branch can die without disturbing the neighbouring branches. They may even take advantage to stretch out further. But each branch shares the resources distributed towards the crown with the whole of the photosynthetic colony. The shape of each branch is part of the architectural whole, making up the tree’s collective memory. Recent studies have shown a genetic differentiation between successive branches. Infinitesimal, yes, but enough to be detected, and to confirm that trees are made up of parts that are partially independent, but that are contributing to the life of the whole.

Quercus dominates his part of the forest, and tries to make the best of what his environment offers. But, nevertheless, he remains on diplomatic terms with the other trees; ecological, physical and chemical transactions with neighbouring trees contribute to the construction of each one. Thus, Quercus has at time needed – and still needs – his neighbours. He exchanges nutrients with them via the mycelium they share. They all receive volatile molecules, and Quercus emits them himself. He keeps his distance from his neighbours because he’s shy, because he knows where they stand. But how far does his diplomacy go?

* * *

Today, as I observe the juxtaposed crowns of the trees, it’s clear a sort of equilibrium has set in between Quercus and his adult neighbours, with dominant trees, co-dominant trees and dominated trees. Several young trees wait in the shadows, making little impact on the adult trees. A beech grows nearby and tries to gain a place. It waits its turn, taking advantage of a few nutrients and informative molecules sent by the adult trees. Its future depends on one of them dying. The dominated trees of today may become the dominant trees of tomorrow.

This forest shows us that plant society reaches a level that animals may not be capable of. Relationships between trees, even of different species, are extremely complex. A balance has been struck between competition and aggressive behaviour, but also between sharing and mutual aid.

PINUS, THE SCOTS PINE, 1870 AND 1892

In which Silva must face a new dramatic episode brought about by human beings. Some go off to war against Prussia, while others do what they can with the few resources that remain. We face a major fire, which eradicates large spaces of heathland, leaving behind a sand desert colonised by eagle ferns. Silva’s best ally will turn out to be a stranger, sought out by human beings. This episode means decisions about forestry are for the first time put down in writing.

The year is 1870, and then 1892.

In 1866, a coalition of several German states under the direction of Prussia invades Austria. The Prussian Prime Minister has become so powerful, he is feared throughout Europe. After several misunderstandings between France and Prussia, the two countries declare war in July 1870. The French troops are poorly prepared and defeated several times. They must retreat all the way to the gates of Paris. The French Emperor Napoleon III surrenders, and the newly established republic’s provisional government is soon under siege in Paris. France signs an armistice on 26th January 1871, and ends up handing over Alsace and part of Lorraine to the German Reich.

This war involved nearly three hundred thousand soldiers. Among them, men in their prime, of course, but also foresters from the prestigious Service des Eaux et Forêts, whose military training and organisation make them good candidates to send to the front, leaving the forests without management or monitoring.

* * *

Quercus is already ninety years old, and twenty-five metres tall. At the edge of Silva, agricultural activity continues despite the war. Livestock requires good grassland. And because it has been practiced for so long, people rely on agricultural burning to regenerate the pastures.

While so many are away at the front, one man starts a fire. Grazing is now regulated, forbidden in the forest – the national imperative is forest recovery. The fire begins at the edge of the forest in an area where new woody growth is starting to spring up. This vegetation has to be eliminated to produce good green grass for the livestock to enjoy, and Homo, in his arrogance, believes he can control fire. But the area is dry and the fire takes on unexpected proportions. Flames break loose; everything begins to burn. Elsewhere in the forest, these fires have become more frequent in recent years, and up until now, they could be controlled on limited land areas. But the war has emptied the countryside, and labour is sorely lacking to control the fires. Some burn for over a span of one hundred hectares.

Here, the fire travels from the village and runs up against the sand of the heathland. A few flames lick at the underbrush, all the way to Quercus. Trees suffer due to intense heat, which leaves surface scars in the form of a darkened layer of rings. Next year, the trees will produce protective tissue to heal potential wounds and begin growing a new layer of living cells beneath the surfaces affected by heat. Fortunately, the consequences for Quercus are not more serious.

The biggest change to the area is that the eagle fern, which was already present, takes advantage of this traumatic episode. It is a pyrophyte: it likes fire because it eliminates competition and, in contrast to many other plants, the eagle fern pushes its rhizomes down into the soil, protecting them against the intense heat of fires. In the forest, wildfires can prompt the stimulation of other ecological processes: for example, some seeds need high temperatures to open. The combustion of plant debris involves a mineralisation of the soil, which is helpful for plants.

But this time, there’s a problem. Many trees are going up in smoke. Worse, the humus has disappeared entirely, and only sand remains. They say fires at that time were so significant, they were impossible to stop, that some raged for weeks before going out. Fires have a lasting impact on the forest, killing the mycelium, leaf litter and microorganisms responsible for providing nutrients to trees. There’s nothing left of any use to regenerate the forest after they’ve passed through, especially when they are recurrent.

Eventually, the forester returns and takes stock of the damage. Historians often say that wars can bring much-needed relief, allowing the forest to breathe a little. While those who live off the forest are away at the front, the trees are at peace, they say. But this time, the war has subjected them to other risks.

When he finds himself in Silva, Pinus must wait for a space in which he can grow. Pinus has a quality that foresters appreciate: he belongs to a pioneering species, meaning he can survive on very little, and likes being the first explorer in a non-forested area. He is frugal, which is lucky as his new territory doesn’t have much to offer. A hole is dug by a forester and his root settles into it. Fairly quickly, the seedling is established, alongside others of his species, thousands of them, which have come to this inhospitable landscape. Right in the sand. Pinus develops the same way as any tree – he begins by rooting laterally, but finding water is not easy in such well-drained soil, and the absence of easily assimilated nutrients limits his growth.

At this stage, Pinus grows very slowly because access to trace elements here is complicated. As the years pass, the outcome hoped for by the foresters who planted him here will come into being: gradually, the pines will lose their needles (which grow back immediately), and although they’re not ideal, these leaves from resinous trees contribute to creating the first humus. Because there’s nothing other than a layer of sand beneath, it will take a considerable length of time for the decomposers to come and inhabit this place. What’s more, fungi, bacteria, nematodes, protozoa, viruses and other insects adapted to pine needle decomposition are rare here. The closest ones have adapted to deciduous trees and can be found under Quercus, at least a hundred metres away. It will take time for this specific ecosystem to form and become balanced.

At this stage of Pinus’s growth, we might question what inspired the foresters to introduce Scots pine into this forest. Pinus is not usually found here. But, as we’ve noted, these trees are frugal. And this is where the solution for forest management lies. Arguments for the introduction of the Scots pine, Pinus sylvestris, can be found in one of the first forest management documents for this forest. In other forests, he’s a true pioneer species that establishes himself easily, alongside birches, those white-trunked trees. But not here. Like all trees, Pinus comes from a seed. A pine seed fallen from a pinecone. The seed was collected and then treated in a nursery, to help with reforestation. Nurseries have sprung up in large numbers since the time when Homo recognised that forests were disappearing and they urgently needed to rebuild them, at a rate of millions of plants each year.

One day, when he was only two or three years old, Pinus was torn from his native soil, along with his roots and plug of earth, to be transported to the unknown. Slowly, Pinus will end up growing and claiming a space in this unstable forest, to the extent that he begins to spread. Once he has reached maturity, he will produce cones whose seeds will sprout with force. Pines spring up among the ferns. Since some of them can also tolerate swampy saturation, they move towards the marsh. This property is also shared by a cousin of Pinus, the maritime pine, upon which Aquitanian foresters rely in their attempt, during the same era, to clean up the gigantic Landes forest. And so the area that was turned into a desert because of fire slowly comes back to life. The forest, resinous now, gradually takes hold on the bare sand.

* * *

The foresters who chose to plant Scots pines in Rambouillet are the first to have had any real sylvicultural training. They are from schools established at the same time as the national forest recovery campaign, which was launched in 1828. While earlier generations of foresters had only a fragmentary knowledge about the functioning of the forest ecosystem, these later foresters have an understanding of ecology that allows them, in 1892, to compose the first forest management document, outlining recommended measures for the next twenty years. The only way for the forest to recover is for it to make new soil, they write, and their best ally for this ambition is the pine, because it can tolerate such sandy and poor soil. Also, at the end of the forest rotation, the pine wood can also be harvested and used. At the time, factories had not yet been built that would transform pines into paper pulp, but the power of the forester was to anticipate societal demand. Sometimes they get lucky. With the Scots pine, they got it right.

By planting so many pines, silviculturists weren’t aiming for a long-term commitment to resinous trees. In forestry, long-term is not the same as in other disciplines. While mature deciduous trees are harvested at more than two hundred years old, the future of these resinous trees is projected to be less than one hundred. Foresters begin planning long-term management forest by forest, plot by plot. They describe their choices in their forest management document, and consider it necessary to convert these softwood forests into hardwood at the end of this first stage. The ultimate goal is the return of the oak. But the oak is incapable of growing in sandy soil, or in humus as acidic as the one left behind by the pines. And so the foresters write down their wish, in black and white: that these pines be followed by a first deciduous rotation, composed mainly of chestnut trees – one of the rare species capable of tolerating these conditions, in particular the acidity of humus made from pine needles.

In making this proposal, they were taking a very long view. Even if pines ‘only’ take one hundred years to mature, it will still be 1992 by the time their plan comes to fruition. The chestnut trees take nearly two hundred years, taking the year to 2192. Thus, the foresters are anticipating and hoping to guide three hundred years of decisions by their successors. And even if history might contradict these choices, the strategy is good: they’re rebuilding a soil that might inspire future foresters. Silva’s humus will be restored, allowing it to once again operate its very complex ecosystem, rather than leaving it as a desert of sand on which only ferns could grow.

HOMO, FROM 1892 TO 1950

In which we enter a difficult period, during which everything speeds up – the spread of knowledge in particular, throwing into question all that we thought we knew about nature and the necessity of preserving it. Conflicts take on global dimensions that affect forests both directly and indirectly. We wonder about Silva’s possible future, and Quercus’s place in it.

We move from the end of the 19th century to the beginning of the second half of the 20th century.

As forests slowly regain territory in Europe at the end of the 19th century, debates about science and nature enter a new phase. After his great voyage around the world on board HMS Beagle, Charles Darwin returns with his theory of evolution by natural selection, which contradicts creationist theory. No, species were not created by God. Instead, Darwin believes that each living being has a natural history that took a considerable length of time to unfold, one that’s still ongoing. People also begin to notice the extent to which species are related to each other, and perceive that they have learned to evolve together and in relation to their environment.

On the other side of the Atlantic, Henry David Thoreau has thrown himself into meditative reflection on humankind’s place on Earth. Isolating himself in the forest like a hermit, he denounces the modern way of life, which, focussed on society’s economic evolution, is beginning to seriously distance people from nature. During the same era, John Muir, from deep in the Yosemite Valley in California, spends his days observing the precious nature offered up to him, and describes for the first time the ecology and spatial distribution of a tree, the majestic American sequoia. The ideas of Thoreau and Muir give rise to a new perception of ecology and landscapes. Feeling that conservation efforts are insufficient to safeguard wonders of nature such as Yosemite Valley or Mariposa Grove, Muir founds the Sierra Club in 1892, one of the first ecologist and activist organisations in history. In 1903, American president Theodore Roosevelt takes up his cause.

* * *

In Europe, following in the steps of Rousseau a century earlier, several small groups have for a while now been concerned about how distant human beings have grown from their natural environment. They believe Homo is losing his roots. One such group of artists gathers in Barbizon, in the Fontainebleau forest. It’s not Muir or Thoreau’s ecological thinking they embrace per se, but a romantic vision of the forest. The woods are finally beginning to flourish again, bringing back a taste for simple values, contemplation and serenity. Their forest refuge makes them aware of the benefits of living near trees, and they lobby to create the first nature reserve, called an ‘artistic reserve’, on a few plots of this large forest where they go to recharge and be inspired. For the first time in France, part of the forest will intentionally be returned to Mother Nature.

Still, these changes in the perception of the forest don’t lead to an evolution of human society. People continue to grow more and more distanced from nature. As Homo moves to the cities, the countryside becomes woodland. But the forests have been indelibly changed by the history of human beings. And the history of Silva is marked by several phases.

During the First World War, certain forests in the east were completely destroyed. Others were machine-gunned from all sides. Living tissues healed over the bullets completely and if we tried to harvest those trees today, the chain of a chainsaw might catch and break apart as it struck a hidden pellet. It would take an expert eye to detect these foreign objects in the wood. The war’s tragic events mutilated so many living beings; what do we do with wounded trees?

Left to nature, their powers of regeneration are impressive. Today they provide exceptional habitats; the wounds inflicted on the old oaks led to the development of a multitude of cavities and pollards conducive to tree biodiversity.

* * *

Our Silva of Rambouillet fortunately did not live through these dramatic events. At the beginning of the 20th century, Silva is finally restored. But their face has certainly changed. The fires of the past have led to a significant number of pines. Foresters have reorganised the management of the massif and established sections grouping several plots, on which cuts of coppice are permitted. This is how all the hornbeams to the east of Quercus came to be cut down at the same time, engendering a violent opening of the underbrush.

Further east in the forest is another open space, once again related to a marsh. Not so long ago, France had only thirteen per cent forested land, and now people are keen to fill the empty spaces with trees. This marsh is once again planted with pines. The operation is not that simple, however; wild rabbits eat everything the foresters plant. Foresters have no choice but to pour considerable resources into attempting to control – or eradicate – the rabbits, beginning with the installation of fences around the plantations, a new technique.

But it’s not enough. Under the leadership of the Water and Forestry administrators, the forest is divided up into lots that people rent for hunting. Renters are required to kill one thousand five hundred rabbits per year, in addition to other game. The rabbits are even dug from their warrens, yet still they persist. So Homo pulls out the big guns. Literally. Anti-personnel landmines are employed to destroy rabbit warrens! Weapons of war, made for humans to kill each other, are now being used against nature. But even the mines are in vain. Only the myxomatoses virus will, much later, eradicate part of the rabbit population and bring a reprieve for foresters.

Rabbits are not the only ones who pose a problem for regeneration. Beginning in 1914, when humans left the area to battle each other, the deer population shot up – and young seedlings were their victims. Administrative hunts were organised, and meat was given to families of the men at the front.

* * *

When the men return from war, the countryside changes again. The train now allows for easier access to the forest from Paris and so the first tourists begin to appear, travelling down for the weekend. This mode of transport is too slow for day labourers, however, so cabins are built onsite to accommodate the families of loggers. Sawmills are set up at the edge of the forest. Most of the firewood is converted into charcoal immediately after harvest so it is easier to transport. It mainly goes to Paris. Some trees are also cut down to make beams used in the development of the mining industry.

In this way, Silva is carefully tended, but at what cost? Ever since people figured out how to extract the maximum profit from the woods, and its management became a science, the forest has been fundamentally changing. The surface area continues to grow, but little by little, Silva’s appearance changes. Exploitation after the period of regeneration has resumed, and herbivore populations continue to swell to dangerous numbers, reducing the forest’s resilience. Thus, the trees get older, but they stop producing fruit. Silviculturists grow seriously worried about forest renewal.

* * *

Twenty years later, a new war breaks out, and once again forest management is challenged. The question of heating has become crucial during some particularly cold winters. The coppice is greatly depleted, well beyond the standard quotas issued by the forest managers. The Allied landing in 1944 requires the terrain to be prepared for eastbound troops. The forest is the ideal place for soldiers to hide, and it is bombed in an attempt to drive out the Germans. Some forest plots are scarred with dozens of bomb craters. Today, some of these holes are full of water and hold amphibian populations, such as the spotted salamander. A plane is shot down by the Luftwaffe, and crashes only a few hundred metres from Quercus.

During the post-war review, the army makes a decision which will change Silva’s future. Communication during the war had been a problem; for an order to travel from command to troops, it sometimes took several hours, or even days, while enemy troops advanced rapidly – a contributing factor to the disastrous defeat of France at the beginning of the conflict. The threat of a new crisis must be anticipated at all costs. People turn to the forest and a unique resource it offers.

* * *

The foresters’ original ambition in cultivating Scots pines was to reconstitute the forest soil before rotating plantings of various deciduous trees. But, by around 1950, the French State has other plans: the pines should become telephone poles. By then, however, the trees were already too old to be suited to this purpose. The instructions sent to the Water and Forests Department were simple: ‘Cut them down and plant young pines!’ This openly contradicted the plan made in 1892 to eventually replace the pines with other species.

Replacing them with new pines won’t help advance biodiversity, but it is practical; in twenty to thirty years, these new pines will have grown into perfectly straight trunks of the right diameter for telephone poles. As France advances into the age of mass communication, it becomes imperative to connect up the countryside. The goal is to set up telephones in every home, and for this, millions of telephone poles – millions of graded pines – are needed.

* * *

The National Forest Fund was created in 1946 to support the new forest policy, of which the need for pines is just one component. France must also continue to increase its overall forest area. The woods have grown, but not fast enough. Investments are made to convert abandoned agricultural land, as in the Morvan and Limousin areas, into forest. Throughout the 1950s and 1960s, more and more trees are planted; not just Scots pines, but other species too, such as the Douglas fir, an evergreen imported from the Americas which is popular in construction. A new evergreen rotation has been instigated to meet the needs of the postwar boom.

It soon becomes clear that the trees are taking too long to grow. Modernity is in a hurry! Luckily, in the meantime, the concrete telephone pole has been invented; more reliable and solid, and above all, faster to produce. The pines have not yet reached the required size, so they are already redundant. The foresters must work with the developing timber industry to organise another commercial use for these trees. The foresters at the end of the 19th century hadn’t anticipated this turn of events. Forestry is subject to hazards whose time scale sometimes exceeds it. The forest grows much more slowly than human politics or technological advancement.

* * *

Quercus most likely thought nothing about these events. He’s just a tree. But perhaps the return of deciduous trees nearby did satisfy some need of his, since he’s so gregarious and communicative. Quercus was saved from the demands of the economy, along with his immediate neighbours. Only the coppice suffered through this period, while the tall trees of the forest were able to continue growing. Quercus’s trunk has grown thicker; he is gradually assuming his dominant position in Silva.

QUERCUS, 1953

In which Quercus provides support for a considerable number of other organisms. We learn that the structure and composition of his bark constitutes both an almost-impenetrable rampart and a refuge for other species. We understand that bark is an ecosystem in and of itself.

The year is 1953.

Since he was young, Quercus has had all the constituent parts of a tree: a trunk, roots, branches and leaves. To protect himself from attackers, he developed complex and chemical immune features, and physical barriers such as solid bark. But, unlike older oaks, the bark of younger trees is mostly smooth. It’s only after a few dozen years, in trees over fifty, sixty, or seventy years old, that we see them develop a textured epidermis that alternates longitudinal strips and cracks, creating the effect typical of oaks. With time, this bark thickens and hardens, becoming fundamental protection for the tree. While temperatures below smooth bark can climb higher than forty degrees, it’s rarely above thirty beneath the bark of an oak. This helps protect the living tissues and avoids the sap overheating, making this species of tree more resistant than others. At more than one hundred and seventy years old, Quercus’s bark is a separate environment in and of itself, like a whole ecosystem supporting a multitude of species.

The trunk climbs towards the sky, showing signs of certain irregularities. Various organisms have taken advantage of the available surface – their spores, carried on the wind, have landed on the bark and anchored themselves. Quercus is not subjected to one particular contamination. A number of lichens have grown on the bark – for example Pertusaria pertusa, which forms a sort of tiny grey ball, with two minute hollows. They almost look like pig noses. Others resemble lettuce leaves – we call these ‘foliose’ lichens. On Quercus, a group of usnea sits at the beginning of the crown, while shield lichens, or Parmelia, form thick spots along the trunk. The battle for the surface of the bark is raging. In many cases, the bark is just a convenient surface, and these species have absolutely no impact on what happens beneath it. They may slightly reduce the rare possible exchanges with the outside, if the bark tissue has some chlorenchyma, which can occasionally support photosynthesis in the spring – but even then, the effect on Quercus is negligible.

Alongside the lichens, bark fissures offer protection from rain and other dangers. Animals take shelter here because many predators aren’t able to reach them – or at least not in principle. But several species have adapted quite well to these very particular living conditions. Nearly fifty per cent of forest spider species are dependent on barks. Among them, a Clubiona corticali (sac spider) is still sleeping behind the slight outcropping it found high up on the tree, waiting for night to fall. When it comes out, it will attack lost caterpillars on the branches, and return at dawn to its subcortical shelter.

Further up, psocoptera, or booklice, have spread out around the lichens and mosses to feed on them. When a parasite fungus appears on the bark – for example, a spore spread through the air looking for bark to colonise – these insects are quick to consume it, providing an efficient cleaning service for Quercus. These psocids are fragile, and rely so completely on the protection of fissures in the bark that they have almost lost their wings. However, they have large eyes to keep watch for predators.

A particularly fearsome example is the voracious pseudoscorpion. This very small creature doesn’t have the stinger we know scorpions by, but like them, it has two pincers, at the end of which venom glands allow it to efficiently immobilise its prey. The problem with this predator is that it can’t bite or grip its prey, cut it up or chew it with its mouth. So the pseudoscorpion has developed a method of its own. With its oral parts narrowed into a needle-like shape, it perforates the prey and injects a particularly active form of saliva, whose powerful enzymes paralyse and then digest the prey. The insect – still alive – feels its viscera liquefying. All the pseudoscorpion needs to do now is suck the fluids from the body of its victim.

* * *

So, the life forms on the trunk include species that want to exploit the tree, but also those who protect it. Quercus grows thanks to the fluids circulating just behind his epidermis. A wound on his trunk would allow organisms to take advantage not only of his heartwood, but also of the nutrients and water transported in his sap-conducting vessels. As a defence, Quercus has poured lots of tannins into his bark, and these complex molecules render the wood undigestible. Here, tannins can represent as much as twenty per cent of the total makeup of the bark. For most organisms that might attempt to attack the trunk, this barrier is impassable. Suberin, the predominant tannin, whose composition is similar to the lignin the wood is formed from, is a sealant – it helps caulk all holes to prevent water loss. Suberin also filters which molecules are allowed to enter, and which must stay outside. Also present in the roots, it forms an impassable barrier, acting as a kind of ultra-selective security guard, and undesirable molecules have no chance of getting past it. This tannin also ensures a thermal buffer to the outside by enclosing air inside the bark, insulating the tree against the chill. The air ensures thermal protection in winter, but also in summer. In short, this tannin is the tree’s frontline of defence.

But suberin is not always enough to stop attacks. There are times when piercing, sucking insects manage to reach the living tissues under the bark, penetrating the phelloderm, or even the phloem. On beech trees, whose smooth bark is thinner than Quercus’s, mealybugs, Cryptococcus fagisuga, manage to pierce the wood. Sometimes, the predators of these mealybugs, such as heteroptera, fail to control them because they are so numerous. Other species wage war against the grainy, thick bark of the oak.

In case of attack, the tree’s repair cells must react as efficiently as possible, but these insects use phytotoxic substances to alter them. When the tree reacts in the usual way, the process of scarring doesn’t work, and the parasite continues its pillaging. The plant must then isolate the harm to prevent it from spreading. This is when tissues of an incredible density begin to develop, formed with ultra-rigid lignin. The tissues attempt a break to stop necrosis setting in, first in one direction, then in another. The result is wood tissues that grow in all directions, giving rise to a burl. In some cases, the tree develops a burl that makes up of a multitude of small knots (dormant buds) emerging from the trunk at the site where the bark was pierced. These young lateral stems produce the sugars and tissues that allow the tree to isolate the emerging injury. Once their mission is accomplished, if sunlight at this level is lacking, these stems are quickly abandoned. Around them, the tree continues to function in its usual way. It even grows around the burl, covering it completely. In a few years, the attack is forgotten.

In most cases, the tree succeeds in fending off insects’ attempts to break through the bark. The burls that develop have extraordinary shapes and colours and are highly sought after for marquetry. They are sometimes referred to as ‘tumorous growths’, which is erroneous – they are in fact the response to an external attack.

Sometimes, in spite of all its protective measures, a breach still opens on a tree. In Quercus’s case, a cavity formed in his trunk after a branch fell. The space was not left empty for long, and a cleaning service began its work.

* * *

Nearby, a colony of ants, Lasius brunneus, had moved into the underbrush, close to a clump of Molinia – a tall grass with a blue tinge in spring. They gathered earth to build a dome on the surface and a nest beneath. These ants are foragers who are constantly exploring. One of them had found a line of sap-sucking insects on Quercus’s bark – aphids that had comfortably settled into a bank of moss, Hypnum cupressiforme, attached to the base of the trunk.

The ant went back and forth several times to bring honeydew, a sugar-rich secretion found on the abdomen of an aphid, to its colony. Next, a long row formed, with other ants following the molecular trace of trail pheromones left by the forager ant. The pheromonal trace was plain enough and the message, crystal clear, even more efficient than road signs: ‘Follow the scent. Very rich food at the end of the path.’ Then, out of curiosity, some went further up.

There must always be scouts, great travellers ready to brave the unknown and conquer new territories. And that’s where they discovered the breach in the tree, left behind by the branch that died and fell to the ground. The cavity would be perfect for housing the colony. High up from the ground, protected from humidity and rain, it would be easier to control the hygrothermal conditions in the nest. The colony moved in and became much more secluded than they were in their nest on the ground.

The Lasius ants now form an unbroken column leading to the aphids’ honeydew. But is this a problem for Quercus? Not in the least. With these ants, the tree has a guaranteed cleaning service. The sap extraction will be short-lived, and the tree will manage to heal.

Since he doesn’t have nerve endings, Quercus probably doesn’t feel all these little feet scurrying along his bark. In many cases, the oak is unaware of what’s happening on his surface. But all that matters is that nothing pierces his epidermis … and he seems, this time, to have been spared such an attack. Quercus stands solid.

QUERCUS AND HOMO, 1970

In which we enter a new period of technological development that once again radically changes the physiognomy of the forests. We discover that the fears of tree-lovers are unfounded, and that modernisation can actually lead to more mature forests. We realise that typical tree biodiversity has been absent from the forest for centuries and will only reappear gradually, according to conservation policy. Finally, the organisation of forest management is turned upside down.

The year is 1970.

Quercus is now more than one hundred and ninety years old. He is over thirty metres tall and reaches slightly higher than the rest of the surrounding trees. Now, he begins to have trouble inducing sufficient evapotranspiration to pull the raw sap molecules higher up in his tissues. The ubiquitous sand beneath a fine layer of silt limits the soil’s capacity to retain water. Gathering enough energy to power the plant pump above grows more complicated. This is why Quercus almost stops growing any taller. Still, he continues to produce great quantities of wood, and leaves – up to seven hundred thousand a season, or three to four tons of leaves per hectare. The branches bend beneath their weight, and the architecture of the tree changes. Luckily, wood fibres, which contain cellulose, hemicellulose and lignin, are flexible enough to handle the resulting tensions and distortion, otherwise the branches would break. With such a huge number of leaves, Quercus has a surface area in contact with the atmosphere of seven hundred square metres. His millions of cells are chemical factories combining air and water to build wood. To make a kilogram of carbonaceous material and two hundred litres of water each day, Quercus has to pump up to four thousand cubic metres of air. He’s an incredible machine, in the prime of his life.

Up until the Second World War, heavy forestry work involved draught horses. While these animals were powerful, they were not strong enough to haul trees as large as Quercus. His imposing size may in fact be what saved him. Quercus has been allowed to grow old in peace. Fagus and others of her kind were also allowed to continue growing, as the beech trees’ wood deteriorates so quickly after being cut, it’s usually impossible to carry them out in time.

* * *

But human ‘progress’ is still radically altering the approach to silviculture. By the 1970s the agricultural industry has become mechanised. Tractors multiply the labour power of farmers, and they flood the world of forestry, too. The chainsaw has become indispensable to loggers. Invented between the two wars, they were initially very heavy, but the industrial progress of the 1960s resulted in the construction of smaller, more flexible machines, and it’s become much easier to use them in the forest. It’s now possible to cut down many more trees with fewer workers, and the timber industry is organised accordingly. Forestry personnel become more specialised. During the decades that follow, the first large oaks fall around Quercus, while the neighbouring pines are replanted to make paper, palettes, furniture and flooring. The coppice continues to be cut, because the inhabitants of the surrounding villages need firewood, so hornbeam and oak coppices are maintained. In contrast, deeper into the interior of Silva, the young coppice regrowth is left to become large forest trees, in the hope of producing specimens with the stature of Quercus. We might have thought that industrial progress would involve a massacre of the forests. But paradoxically, because technological developments make harvesting wood easier, people can now let the trees grow older and taller. In their mastery of nature, they will still be able to use them.

* * *

What seems to be in store for Silva, then, is the appearance of more large trees, with widespread maturing of oaks and beeches in particular, which are growing in the forest at a rate that hasn’t been witnessed for centuries. Foresters become ever keener to preserve them. And slowly, we observe the unexpected return of certain species that had previously disappeared from our forests.

For centuries, hedges were needed to protect cattle, offering shade and leaves, the lowest of which could be eaten. These hedges also had the function of retaining sediment, fine particles rich in nutrients for cultivated plants. Trees were sometimes trimmed to provide supplementary food for animals, leading to injury – cavities of all sorts appeared in the pollarded hedge trees, which began to decline, transforming into refuges for all kinds of creatures.

These habitats, on which nearly thirty per cent of forest biodiversity depended, had all but disappeared. In the second half of the 20th century, the ageing of Silva’s trees encouraged the return of forest species that had been banished from their original living environment to the forest, at the same time as field hedgerows were cut down to enlarge plots and make them easier to cultivate with tractors. From this joint history, hundreds and possibly thousands of species that had been reduced to very low numbers from the Middle Ages until the end of the 19th century, begin to make a comeback in the forest.

More than ever, silviculture becomes a science that adapts to each situation, forest stand by forest stand, according to local conditions. It becomes refined, drawing on the work of predecessors to achieve the best yield. The number of forestry schools that now train loggers, technicians and forestry engineers, multiplies. The government department that manages Waters and Forests encompasses too many activities, so the structure of the organisation is modernised. Waters and Forests are separated in 1964, creating the National Forestry Office (NFO) and the Water Agencies. The NFO is tasked with forest policy only on State land and in municipalities – a third of the wooded area in France. Ultra-specialisation begins. For managing private land (two thirds of French forests), people now organise into cooperatives, landowner associations, forest management societies and other systems.

* * *

For Quercus, a fundamental change with the creation of the NFO is that, unlike under the former administration, taxes from citizens no longer fund the management of this forest – the organisation is required to be financially self-reliant. From that point on, Silva must provide all the income for those who work in the forest, almost without State financial aid. And so, because its budget is no longer externally dictated, management can finally be more focussed on a long-term vision, in which priority can be given to the goal of producing a specific type of wood to supply the industry, alongside other objectives.

* * *

One of these new objectives quickly presents itself: welcoming the public. Indeed, lifestyle changes, with workers having more paid time off and more free time, means more people seeking the peace of the forest. In the 1970s, networks of paths through the forests are developed for this purpose. A few hundred metres from Quercus, a paved route is put in, to allow visitors on bicycles.

These changes in forestry policy lead to better management of lumber. Trees are sold more efficiently, and the forestry economy allows for long-term investments, ensuring financial balance on a national scale. Income from the most productive forests supports struggling ones, such as those in the southeast where the extremely dry land means that first and foremost, a fire service must be created. Now that production is in hand, there is the opportunity to develop a strategy around conservation and growing high-quality wood. Looking further ahead, imagining the forests of tomorrow, or the next century, the tallest and most beautiful trees must last. And so Quercus can continue to grow.

During this period, some foresters have begun to ask questions about the future of their forests. They wonder if some species are suffering from the strategy of production at all costs. For example, a forester who kept a tree with a woodpecker hole, a potential home for several rare species, would be looked down upon or even reprimanded. Some saw woodpecker holes and dead wood as signs of poor management and even an environmental health risk; after all, people believed for a long time that vermin could be harboured in damaged or rotting wood. Growing knowledge about microbes in the late 19th century fortunately revolutionised these beliefs. But even though it has been common knowledge since Pasteur that our health problems don’t come from dead trees, the narrative is particularly hard to shake. A healthy, well-managed forest, many believe, is a clean forest with no dead wood. Additionally, many people worried that dead trees could be carriers of germs that could affect healthy ones. But here, too, beliefs are slowly beginning to change; many trees die of entirely non-contagious causes.

During these decades, while many people see only economic interests in natural spaces such as the forest, others observe that nature is suffering. In 1962, Rachel Carson publishes Silent Spring, in which she discusses how pesticides are changing agricultural landscapes to the detriment of birds, which are disappearing. A global environmentalist movement begins, fighting for the protection of species across the Western world. A decade later, in 1972, scientists Donella Meadows, Dennis Meadows, Jørgen Randers and William W. Behrens from the Massachusetts Institute of Technology publish a report called The Limits to Growth, explaining for the first time that planetary resources are limited. They identify possible trajectories for our demography and economy, and explain that, without a global awakening, our societies will enter a sharp decline. Resources are finite, and nature has limits.

Many people can’t accept this, arguing that the scientists must be mistaken. But a movement is launched, and anger is mounting. In many areas of the world, there are calls for environmental protection. Not so long ago, in 1948, several states created the International Union for the Protection of Nature, which became, in 1956, the International Union for Conservation of Nature, a non-governmental organisation whose primary mission was to assist states in implementing policies for the protection of biodiversity. But strong actions were needed in all parts of the world. The 1970s sees the introduction of conservation laws in France, Britain, and many other nations.

DRYOCOPUS, THE BLACK WOODPECKER, 1992

In which we encounter a newcomer to Silva and discover the awkward yet endearing qualities of a bird whose role as an engineer is crucial for the development of arboreal life. We learn that the presence of this bird, the black woodpecker, constitutes clear evidence of the recovery of European forests, and that its return also signals the reappearance of other species whose benefits for Silva are undeniable.

The year is 1992.

It’s late evening in February and I’m sitting at the foot of Quercus, waiting for night to fall. I can feel the air filling with humidity from the neighbouring marsh. A blackbird and a robin sing a few notes, signalling their presence in this territory. When the dampness seeps into my clothes, and I have to shift position against Quercus’s enormous trunk, the majestic bird that rules over Silva makes itself known. It calls out once, sitting at the top of a tree a hundred metres or so from where I am, one note that lasts longer than the second, signalling its arrival in the kingdom of the canopy. A note that is at once eloquent and timid. I seek it out, catch a glimpse of it between branches. For several minutes it flies around me, keeping its distance. It’s trying to approach, but my presence is intimidating.

It’s clear that I’m disturbing this bird and so it’s time to go. I should leave it in peace, and allow it to get back to its home. Just after I step away, the bird enters a hole in one of Fagus’s master branches. This cavity is several decades old. The brief apparition of the bird testifies to the emergence of a new wave of species who are navigating the territory of their neighbours. This black woodpecker is most likely a descendant of the first Drycopus to return to Silva in the 1980s.

* * *

Dryocopus is a solitary creature who likes quiet and hates invaders. But other species come along to pester him and steal his cavity. A stock dove comes first – a fairly unobtrusive forest bird that will only settle in large, spacious tree cavities. It’s a rare bird to spot because it is so particular about its lodgings. Another bird who appreciates the work of the woodpecker is the tawny owl. Cohabiting with tawny owls is tumultuous because they too are very territorial, and, with their powerful claws and beak, they have the tools to defend themselves. When their chicks are big enough, they are all that can be heard in the nighttime forest. A couple of tawny owls have already settled into the hole that the woodpecker drilled when it arrived. Now Dryocopus has to give up his home and peck another one.

The black woodpecker, Dryocopus martius, is, as its name suggests, a black bird, fairly large with a red cap, found mainly in the forest. But not just anywhere in the forest. For it to settle, it needs a large oak. Competition with other arboreal species is fierce, but the woodpecker is one of the few who can bore into the very hard wood of this deciduous tree. Since the Middle Ages, its numbers gradually declined along with the forest, and the remaining woodpeckers sought refuge in a few mountainous forests in central Europe and Scandinavia. To re-conquer Europe, the species had to wait until the 19th century for the change in forestry practice and the slow return of old oaks.

In the 1960s, the black woodpecker began returning to France and quickly reclaimed its territory. Some slower species followed, such as the boreal owl and the Eurasian pygmy owl. But in the lowlands, it remains a true success story of the return of species typical to old, tall trees.

Quercus and Fagus are not complaining. The arrival of the black woodpecker in Rambouillet in the 1980s meant an increase in housing options for owls, who live in the holes it bores. And owls eat rodents, those enemies of acorns. To hear the evidence, all you have to do is stroll through the forest at night: like the woodpeckers, owls have well and truly regained their place.

But even if the trees are content, Dryocopus is annoyed. With all these freeloaders, he’s got his work cut out. Dryocopus is a solitary creature, and monitoring his territory is complicated. He also needs to feed himself. Saproxylic insects, which develop in dead wood, are his food of choice – he detects their presence by picking up their vibrations, and digs them out with his exceptionally long tongue. But humans have been collecting dead wood for centuries, so his prey is a rare treat. Dryocopus also likes wood ants, notoriously touchy large red ants that ‘sting’ violently when they feel they’re being attacked. To ward off the jets of formic acid they project from their abdomens in lieu of a real sting, nature has bestowed upon the woodpecker a layer of wax that protects his plumage. He will sometimes even stir up the ants just to get a little of their acid on his feathers, as it helps keep parasites away.

But like so many species, wood ants have suffered from human intervention. When pheasants began to be bred for hunting in the 19th century, campaigns to collect entire colonies of wood ants to feed the young pheasants were launched. As a result, they all but disappeared from Rambouillet after a few decades. Their return to the forest has been slow.

* * *

Dryocopus was born several kilometres from Silva, in a small, forested valley. After a few weeks, he moved to this new territory, still virgin to the species, and bored a hole into one of several large oaks with his strong, solid beak. The hole had a very large opening and was more than fifty centimetres deep. Once he had moved in, Dryocopus spent his days searching for prey, eating and signalling his presence. He lets out long, plaintive ‘pi-uuuu’ calls anytime he stops to rest in the treetops, and makes little trills when he flies. He loves home so much and is so territorial that it’s possible to predict his activities almost to the minute. For those of his peers that dare approach today, he also drums high in the branches, where the wood resonates over great distances. No species could ignore the fact that the wood-pecker is here.

And yet, the following spring, pigeons moved into his space. Dryocopus had to bore a new hole. This time, he chooses a vertical joiner branch of Fagus, just across the way from Quercus. Boring holes in the hardwood of beech trees takes a lot of energy, even for a professional like Dryocopus. So he gets into the habit of coming back regularly to monitor his nesting area and make sure no one is in his nest. He flies close by, calls out, makes himself known, flies away and then watches from a distance before coming back quietly. So much playacting. Dryocopus hopes to be able to enjoy this home for a long time.

But just a year later, he’s disturbed again. This time by a pine marten, a mammal the size of a cat that climbs trees to eat smaller animals hidden in holes in the trunk. Best to avoid it – it’s a fierce creature.

Dryocopus has good reason to be aggravated. He flies off to bore another hole in a beech a little further away.

* * *

With the arrival of the black woodpecker in our forests, we begin to give pride of place to species typical of the final stages of a forest’s development. The hole bored into Fagus has created such a large opening in the beech tree that multiple organisms now have access to its heart. As long as vertebrates like birds or mammals come and nest inside, the interior will be regularly cleaned, limiting the degradation of the wood, and the cavity can be enlarged, particularly in terms of height, without threatening the sustainability of the tree. However, the tree is losing its commercial value, because the heartwood is affected. Still, when we combine economy with ecology, the assessment leads us to reconsider the issue: the woodpecker wants to conserve its energy, and thus doesn’t bore holes very often. As a territorial creature, it can be satisfied with the same nest cavity for many years without moving, and prevents any other black woodpecker from moving into the immediate area. So, in theory, maintaining the tree that holds the nest confines the bird to this tree only, meaning that other beeches are preserved.

SILVA, 1992

In which the sky falls on the treetops, to their great misfortune. We discover that even while forests grow taller and trees grow wider, both can be affected by an unknown disease. Monitoring networks are put in place in all countries of the northern hemisphere. The disease is planetary. We see the birth of forest monitoring.

The year is still 1992.

Certain mutations signal that Silva is entering a new era. The forest has been shifting into this new period for a while already, possibly for more than a century, but the change is happening slowly. Little by little, the ambient air has changed its chemical composition. When Quercus was born, there was a balance between various particles – of atmospheric nitrogen, carbon and oxygen, but also water and other components. Over time, however, this balance has deteriorated. Imperceptible changes show up in this chemical composition, and new molecules have entered, including some that are toxic and do not occur naturally. The latter change the way plants react. Many of these particles were already present in the Earth’s atmosphere, but that was more than a billion years ago. It took a long time – it’s hard, really, to imagine just how long – for life to become established and gradually change the nature of the air, rendering it breathable, particularly for the animals we are. For Quercus, feeling molecules of carbon, nitrogen, oxygen and water around his leaves is normal – all have a role in his breathing and the production of chlorophyll. But now, certain particles have increased. Nitrogen was first, which is naturally dominant in the atmosphere. It increased further with the rise of intensive agriculture, which is now dumping nitrate-rich fertiliser to encourage the growth of cultivated plants. The targeted plants consume this supply. But nitrogen doesn’t come alone. Carbon dioxide, ozone and methane come along with it, as well as chlorofluorocarbons, among others. The air is increasingly filled with these particles, and they are not without impact. Carbon in particular is received by Quercus, Fagus and all the others, who eagerly assimilate it to make even more tissues. The trees begin to grow faster.

* * *

But this rush of new atmospheric molecules also brings problems. Silva is now subject to a new attack. Without knowing why, we observe, from the 1970s on, that certain trees are dying for no apparent reason. In the Vosges, and at the edge of the Mediterranean, entire forest stands of silver firs and Scots pines change colour right in the middle of their growing season. Beech and oaks are close behind. The needles or leaves go yellow and, in many cases, fall. This phenomenon accelerates in the 1980s and becomes international. Whole sections of mountains turn yellow.

Foresters grow worried and set up a forest health surveillance network, called Le Reseau Bleu. There hadn’t previously been any process for monitoring the forest because people never imagined they would confront a crisis threatening tree health, especially not in several species at the same time. It is now necessary to record careful observations that might explain what’s happening. Over one thousand six hundred plots are spread out over the national territory, where two types of observation take place. The first is to examine how the canopies are changing, and the second measures the growth of certain trees by boring into live trunks with an auger, to count the rings and establish growth curves, particularly over the trees’ last few years of life.

This monitoring network begins by identifying pathogens, fungi or insects that sometimes affect local stands of trees. It soon becomes clear that the spread of dieback is such that the scale of observation must be expanded to include all neighbouring countries, which in turn put dedicated systems in place. Every country from Spain to the USSR participates, and all make the same observation: young or mature, trees are withering in massive numbers, with no relation to forest management. The phenomenon is international. But the question remains: why?

The answer will eventually come from air quality specialists: the sky is falling onto our treetops, and it’s full of undesirable particles. Sulphates, nitrates, nitrites, ammonium, hydrogen protons and industrial dust. Their combined effects involve a clogging of the leaves, which aren’t able to breathe as easily, and the acidification of rains and fog, which damages tree tissues, also acidifies the soil and affects the quality of leaf litter decomposition, as well as the microbial life essential to the healthy functioning of forest soil.

Temperatures gradually rise. The climate is in upheaval, and with it, Silva. Growth is impaired, and people fear the worst for the future of the forests. Some specialists even think the forests might not survive. To document their reaction to air pollution, two significant developments occur. The first development, in 1999, is the establishment of the Department of Forest Health to monitor the entire forest territory, both private and public. At the same time, a network of more than one hundred monitoring sites is set up, in which the trees are measured and closely observed to see how they establish themselves in the forest, how they live together, and how they react to changes in the forest. The second development is the National Network for Long-Term Monitoring of Forest Ecosystems, which becomes the framework for a life-sized laboratory, the forest in vivo, which involves both the parameters of forest description and the elements that might affect it, such as atmospheric pollutants.

From then on, the forest is under close scrutiny. People begin to realise that nothing is immune – even our forests can be called into question, at any moment. And human beings play a part. Homo begins to ask himself: can a single species change the balance of nature?

* * *

Humbled, foresters must come up with a new approach to protect the future of the forest, taking into account atmospheric pollution and balancing the sometimes contradictory demands of society: they need to preserve everything while still being productive, welcome in more and more visitors while also offering them safe forests, and make sure biodiversity is preserved.

Subject to issues beyond its control, Silva continues to pursue their slow evolution. They were thought to be condemned, hopeless. But in the end, our Silva was only slightly affected by generalised dieback, and acid rain fell on other areas. Just a few kilometres away from Quercus, Homo sets up one of the one hundred and two sites of the observation network in a stand of Scots pines. Silva is transforming into a scientific laboratory – they will now be put under a microscope.

HOMO, 1992 AND 1993

In which human beings become aware of their impact on the planet and organise an international conference to make important resolutions. But there’s no guarantee these good intentions will lead to results. The managers of Silva take measures to allow the different species that populate the forest to settle in and live there, in harmony if possible. But harmony is only relative. Quercus detects, once again, very telling molecules: a new tree sees the end coming.

Tail end of 1992.

Quercus is two hundred years old when, in June 1992, the United Nations organises a conference in Rio de Janeiro. The Earth Summit brings together one hundred and twenty chiefs of State and one hundred and seventy-eight countries. The subject? Our planet. Us. There is talk about planning organised conservation initiatives: Agenda 21 will look at housing, health, desertification, mountains, agriculture, water resources and pollution – particularly greenhouse gases. Biodiversity and forests are also discussed.

Afterwards, foresters who have long been concerned about forest biodiversity adopt new measures. They officially recognise that dead trees and those featuring woodpecker holes have their part to play in the healthy functioning of the forest. Those who manage the public forests are asked to keep at least three dead trees on forest plots, per hectare. With this commitment, they sweep away centuries of forestry culture and beliefs about the dangers of dead wood. A new way of life must be instated in the countryside and among those who use the forests. People still believe a beautiful forest is one that shows its upkeep, one in which you can go for a walk unimpeded – so not too much bracken or dead wood on the ground making it look messy. People like to see animals from a distance, passing through the underbrush, so historically they have wanted foresters to control and tidy the forest.

But now it is acknowledged that a rich forest is one that features the many microhabitats we’ve been eliminating for so long. Undergrowth can be desirable, and woody plants can thrive in the event of a gap in the canopy of dominant trees. We have to leave room for species that thrive on advanced stages of wood decomposition. This change in attitudes takes time, because it means convincing everyone of these factors, from professionals to the general public.

Still, Quercus and his neighbours benefit from the shift. Black woodpecker holes can easily be seen, and the beech trees that contain these habitats begin to be inventoried and preserved. This corner of the forest, a few hectares, is left alone for now, saving Dryocopus’s habitat and leaving the bird in peace.

When these measures were officially adopted in favour of biodiversity in public forests, I was fifteen years old. A little lost, as is the case for many teens, and frequently to be found out biking with friends. In that winter of 1992–3, I had nothing but questions. What did my future hold? What would I do for work? Teenage questions. I would have liked for someone to decide for me, but at the same time, I was fairly discerning – I knew I needed to do something that would satisfy my daily curiosity and bring meaning to my life. For months, I had been asking for a sign that would help me see more clearly.

One day at the end of winter we went riding. The ground in the Rambouillet forest was muddy, but after sixty kilometres we hit dry terrain. I found myself pedaling hard in loose sand. There is nothing worse than feeling like you’re continuously skidding, struggling and getting nowhere. I was at my limit.

Where a cluster of hornbeams formed an arch above the path, my chain came off. I had no choice but to stop. My friends were far ahead. In a state of near-desperation, I lifted my head and was immediately overcome by a strange sensation, something like an epiphany. In that moment, I knew that I wanted to work outside, maybe even with forest animals. I had once come upon a wild boar, in a park where there weren’t supposed to be any, and I often thought about that moment. Now, suddenly, I realised: my calling is here, in nature. I had to think it over more seriously.

I replaced my chain and raised my head again. And that’s when I noticed the oak to my left. It was majestic. This tree had certainly found its place. Surely it knew from a very young age what it was destined for. To grow. To reach towards the light, to stand tall, to last as long as possible. This tree, at least, didn’t have to wonder about its future.

And that’s how I first met Quercus.

* * *

During the spring of 1993, while people are questioning the future of our environment and forests in particular, our oak senses abnormally high quantities of terpene and alkaloid molecules emitted by a neighbouring tree. It’s difficult to identify their exact provenance, but the signal is strong. A tree is in trouble, and trying to fight by putting all its energy into producing defence molecules.

Quercus’s leaf receptors detect these molecules. Given it is a high alert that signals a complete attack on another tree – both leaves and wood – all of his tissues begin production of molecules to limit the concentration of nitrogen in the leaves, which defoliators love, and make sugars to produce lignin. Because it’s hard to discern where the warning molecules are coming from, and because of the high concentration of volatile elements he perceives, Quercus can’t be sure that he himself is not the origin of these emissions. Because they are partly autonomous, one of his branches might be involved without the others yet being affected. It is therefore a priority for him to build up his immunity, and each branch gets ready to provide a collective response from the whole of the organism.

Chemical emissions fill the air and spread throughout Silva’s atmosphere. All the trees detect the same alert signals and have the same reaction. It’s clear that a tree is undergoing a full attack during its bud break. The problem is that the more it tries to defend itself, the more volatile molecules it releases, and these attract insects. Soon they begin to arrive from far off to consume some of the tree’s tissues, and among them is Cerambryx. The end is near.

CERAMBYX, THE CAPRICORN BEETLE, 1997

Silva is the theatre of a new chemical tragedy. As a tree dies, we discover that its defence strategies can inadvertently hasten its end. We meet Cerambyx, the beautiful tree beetle, who heads for the trunk of the dying tree to mate. As the ailing tree issues a last-ditch SOS to the enemies of its enemies, we understand that the death of a tree is also the source of so much life.

The year is 1997.

The imago was on an umbelliferous flower, those large white umbel-shaped flowers that grow at the forest’s edge, when he picked up the distress alkaloid. Since his emergence two days earlier, he has been spending his time eating pollen. Although the larva devours wood, once it reaches adulthood, the imago completely changes its diet. So even though he was born in a tree, he very quickly seeks out the sunny areas at the edges of the path and the forest to find flowers rich in pollen. There, he joins other flower-lovers – bees, flies, hover flies and other Coleoptera, which, like him, have flocked to this place of abundant blooms.

Flowers are crucial to the survival of adult forest insects. The woods that seem so still and quiet are, in fact, humming on all sides. There is plenty of competition, but Cerambyx’s imposing size gives him an advantage. Who would try to attack the Capricorn beetle? Cerambyx is a Coleoptera, a sort of large scarab beetle, measuring two and a half centimetres in length, ten times larger than Neuroterus – the wasp. His elytra, the hard chitinous pieces that protect his wings, are black, granular and shiny. His head features powerful mandibles, capable of cutting through leaves. In the race for sweet pollen, he could easily defend himself against a potential challenger.

And so our adult male longhorn, Cerambyx scopolii, is at ease on his flower the moment that his antennae, longer than his body, detect the molecules of an oak in distress. These antennae are the beetle’s equivalent of a mammal’s nose, and their length increases the possibility of catching all sorts of odours that to us would be imperceptible. This particular odour has a special message for Cerambyx: the time has come for reproduction.

* * *

Cerambyx lifts off. He is a little heavy, but his antennae help him balance in the air. Once he’s on his way, nothing can stop him. He detects various substances, such as phytoncides and other volatile essential oils, but now his goal is to find the source of these alkaloid emissions. He covers several hundred metres, heading straight towards his target. He passes through a sunny area above the path, at the edge of which a couple of black-headed warblers, migratory birds who have returned from Africa to reproduce, lie in wait for the many wood-decomposing insects who are also following the trail of odour. Their lunch is about to be served. But Cerambyx is much too big for them to eat, and continues on his way, alongside a multitude of other insects drawn onward by the promise of a good meal as well as a collective reproduction session, until they finally arrive at the foot of the ailing oak tree.

This oak stands, unprotected, next to a sandy path, which means it has probably taken a beating during periods of extreme heat for several years in a row. Acid rains may also have affected it more than its neighbours. It gradually began to abandon its branches, and then struggled to deliver the sap to the terminal buds, like the parent tree long ago. Now the branches have dried out, and since it can no longer provide them with sap, the oak has had to block the sap-conducting vessels, pooling its energy to create sugars that allow it to limit the loss of fluids and plug any potential openings.

It had trouble fighting all the attacks, resulting in a field day for defoliators. For several seasons, the caterpillars have been on the attack. Now, only a few branches remain green. The leaves came out in the spring with low reserves of saccharose and starch. The cumulative weaknesses of the previous year haven’t allowed the tree to produce the reserves necessary for next year’s bud break. And the buds that are still alive had barely opened when green budworm caterpillars slipped inside. The few emerging leaves that have managed to unfurl have also been attacked. The oak has no choice but to start its growing season while still on the defence, drawing upon its last reserves. It hasn’t had time to reduce the concentration of nitrogen in its leaves, because this cellular modification would have used too much energy.

With very few leaves left, it sends a few tannins and bitter principles towards the wood of the still-living branches. It makes terpenes and alkaloids to reduce the digestibility of its wood, but also as a way of warning the entirety of its plural organism that the time has come to engage in final combat. It produces these chemicals to excess, given the few resources at its disposal, throwing every last ounce of its strength into the battle. Essential oils, terpenoids, phytoncides. The tree quickly tries to slow the progress of the attackers. But the oak is growing weaker. Within a very short time, it won’t produce the sugars that allow it to produce new wood. And no sugars means no indigestible lignin on the tissues closest to the bark.

The insects arrive. Traffic is heavy all over the tree. Oedemeridae, commonly known as false blister beetles, settle on the small branches. Shield bugs drink sap on the few leaves. Beetles trickle in as well, other longhorns such as Rhagium, as well as other beetles, such as capricorn beetles, jewel beetles, weevils, a staghorn, lesser stag beetles, and at the base of the tree, click beetles and filiform beetles, whose larvae favour woody debris. We also see dipterans, such as crane flies and insects with black and yellow stripes called syrphid flies that mimic wasps and make predators believe they can sting. A small colony of red-orange ants, Myrmica rubra, has settled into a slit carved by a beetle, further breaking down of the structure of the wood to make a spacious nest. Moths complete the picture. Each one has detectors on their antennae for terpene molecules and alkaloids, and they follow these traces. Some head for branches that have already been abandoned and died, while others attack the stillliving wood. The unfortunate consequence is that with each attack, the oak produces more defence molecules, which the insects have learned to interpret as signs of weakness – giving them the signal to strike. The tree has entered a vicious cycle: the more insects flood towards it, the more it defends itself, without ever halting their impact, attracting even more insects that help precipitate it towards its inevitable end.

There are certain organisms that help the insects eat the wood. Lignin is particularly heavy and indigestible, and forms the strongest wood cells. Only a rare few are able to digest such a cocktail – mainly bacteria and fungi, and particularly white rot fungi. These fungi make enzymes loaded with free radicals, capable of extracting some of the electrons that bond the lignin’s structure. Like a chemist, this fungus breaks down the lignin, the tree’s last defence against its fall into decay. Breaches begin to open everywhere. A polypore had also sprouted on the oak’s trunk a few years ago, the solid fruit of a fungus whose mycelium had managed to enter the wood. By gaining ground in the tree, this oak mazegill, Daedalea quercina, had begun to decompose wood cells in certain sapwood and liber tissues, secreting enzymes whose role is digestive. Slowly, patiently, it worked to separate the lignin from the cellulose by cleaving their mechanical bonds, and even began to gradually decompose the cellulose into easy-to-digest carbohydrates. In the early days, the oak fought back, and then began, in vain, to isolate the area. The fungus continued its work, paving the way for insect successors.

Their turn has come. Cerambyx lands on the trunk. He knows that if he has detected the tree’s distress, females must also have picked up the signal. He begins the search and finds one only a few metres higher. A short courtship dance ensues, leading to their mating. The female wastes no time laying her eggs in a crevice of the bark. The larvae that emerge will dig their own tunnel in the wood, where they’ll spend between two and three years. To digest the wood, the larvae are helped by a symbiont, another fungus, transmitted by the mother to the surface of the eggs as soon as they’re laid, and now present in the larvae’s intestines, allowing them to break down the lignin. When they’re ready, the larvae will isolate themselves inside their pupal chambers, which they close with a calcium carbonate seal. Meanwhile, the larvae must grow without being eaten.

Cerambyx and the other wood-eating insects that picked up the ailing oak’s aerial molecules are not alone. Some of these odours are specifically destined for carnivorous insects. This is how the tree in distress calls on the help of its enemies’ enemies. The carnivorous insects have also followed the scent and arrive at the scene of an incredible harvest. Potential prey approach from every direction. Some of the predators suck out the lymph, their prey’s vital liquids. Others eat them whole.

Some wasps have found a trick that allows them to reproduce while limiting the effort required to develop their larvae. These ichneumonid wasps, very distant cousins of Neuroterus, have an ovipositor at the end of their abdomen. With this long needle, they can detect the vibrations of a larva nibbling inside the tree. One of the physical properties of dense wood is to effectively conduct sound. They hear the insect and locate it. Then, using their ovipositor to pierce the various layers of wood and reach the larva, they lay their egg inside it. The egg needs to hatch quickly, but not too quickly; it isn’t yet able to digest wood well, so it needs to let the host larva proceed with xylophagy. Meanwhile, it slowly eats the viscera of its host, without ever touching the vital organs. The larva is thereby parasitised, growing weaker by the day, until the young wasp emerges, at which point the wasp deals the final blow. It finishes devouring the larva from the inside before making an exit via a hole in the wood.

There are many cases like this, but not all the carnivorous insects prevail. A few birds or, more rarely, certain bats, will capture several insects a day before they’ve been able to reproduce.

* * *

Throughout the entire growing season, the oak tried in vain to defend itself. Holes of various diameters, corresponding to insects of different sizes, are now scattered across its bark. These breaches allow other saproxylic organisms, such as new fungus or bacteria, to enter. These are already infiltrating and will continue the work of breaking down the wood in autumn and winter. If only these species had attacked just the heartwood, the part of the tree that’s already dead. But no, it also takes its toll on living tissue.

Next spring, this oak can no longer carry sap all the way to the highest buds on its crown. All the terminal branches dry out. The tree dies.

This tree’s tragedy presents an opportunity for so many others. Under normal conditions, wood-eating insects consume only 0.25 per cent of the biomass of trees that are attacked, or less than 0.00001 per cent of the forest biomass. Their role is tiny, since their populations are diluted across the forest landscape. In extreme cases such as the one just described, the tree’s demise is an enormous boost to biodiversity. Thousands of species participate in breaking down the wood. Once dead, the oak will remain standing for a few years before collapsing due to tissue breakdown or attacks by birds seeking prey in the wood. Wind and rain will also play their part as mechanical destroyers. Many microhabitats, such as holes left by fallen branches, will offer cavities that can be used by new species.

One third of forest biodiversity is saproxylic and includes some of the rarest species. For nearly seven thousand years, since the steppe gave way to the forest after the ice age, humans have systematically stripped the forest of dead wood for firewood. In the past few centuries, the reduction of forest area and intensification of wood-gathering have driven saproxylic organisms to seek refuge, sometimes in the forest, but mostly beyond it. At times, their situation has likely been precarious and their survival uncertain. It is estimated that many populations of saproxylic species have had no choice but to content themselves with old trees planted at the edge of roads as shade for horses, or trees kept in groves to shelter livestock. Forest recovery, and then the return of mature forests since the second half of the 19th century, have brought about improvements, but people continue to collect dead wood. Only since recent measures were put in place to keep dead wood in production forests have we seen the return of this very specific biodiversity. Coleoptera specialists even observe the return of certain species identified as extinct a hundred and fifty years ago – a clear testament to the effectiveness of conservation efforts. Their return is a very good sign and contributes to the healthy functioning of our forest ecosystems.

* * *

This oak is now dead, creating an opening in the canopy that helps new vegetation typical of forest clearings to grow. The bramble will flourish here. Young birch saplings will grow taller. The neighbouring trees will take advantage of the extra light to enhance their photosynthetic production, and a few branches will grow towards the opening. All of this is happening just forty metres from Quercus. We could say that this event doesn’t affect him much – and yet …

In dying, this oak has attracted predatory species of wood-and leaf-eating insects, contributing indirectly to regulating pests. It causes a protective response in all its neighbours, including Quercus, who also makes defence molecules, particularly phytoncides. Walking through a beautiful forest where a tree is dying, while it may give the illusion of a forest in poor health, actually means being immersed in an atmosphere rich in phytoncides, which are so beneficial for the life cycle of Silva.

In dying, this tree has become a new source of life. The famous adage by Antoine Laurent de Lavoisier makes sense here: ‘Nothing is lost, nothing is created, everything transforms.’ All the wood molecules from this tree, which remains standing, slowly decomposing, will return to Silva to be assimilated and reintroduced into the system. A sort of Möbius loop that never ends.

The habit of gathering dead wood from the forest to use for firewood still persists; and it’s not within logging culture to leave these rotting bits in the underbrush, in spite of foresters’ instructions. So the dead wood is still frequently removed or, worse, set on fire along with a few tyres and a bit of used motor oil. The forestry world is divided between partisans of biodiversity on one side, and those inclined towards maintaining forest traditions. During a conference I once attended, one naturalist summed up the paradox perfectly, declaring: ‘Let the dead trees live!’

DENDROCOPOS, THE GREAT SPOTTED WOODPECKER, 1998

In which we meet a new animal, who invites himself to Silva’s table. Dendrocopos major, the great spotted woodpecker, settles in by boring a hole in part of Quercus’s crown. We might think this event would weaken Quercus, but discover instead a mutual agreement between the tree and the bird, with benefits that seem reciprocal. Is this a plant-animal collaboration?

It is spring, 1998.

The first light of day has barely penetrated the forest when a staccato sound like a machine gun rings out. There’s a violence to the repeated shocks, resonating all the way down to the underbrush. Any bird other than a woodpecker would go crazy, smashing their beaks against hardwood like this – their neurons would be destroyed in a few seconds. But Dendrocopos drums cheerfully on a hollow branch. A second round rings out, and then another.

Dendrocopos, the great spotted woodpecker, is a cousin to Dryocopus. He won’t tolerate another male of his kind on his territory. This area belongs to him; he assiduously monitors and defends it, listening keenly to his chicks cheeping in the cavity the female has chosen. For the moment, everything is fine, thanks to his practice of marking territory by hammering against hollow wood. His brain survives this battering because nature has endowed him with a cranium that’s very dense at the front and back to offset the impact, with a layer of liquid filling the space between the brain and the skull, a thick layer of cartilage between the beak and skull, and powerful neck muscles that can handle the impact. So Dendrocopos can drum to his heart’s content, filling the forest with news of his presence. His song – because yes, it is considered a song – can be heard for several hundred metres.

To seduce a female in the middle of winter, it is not enough that the male great spotted woodpecker has elegant plumage and a bold red head. He also has to find a territory that meets two conditions: a well-stocked pantry, and a nest located less than thirty metres from said pantry. The large oak that just died in the area near Quercus has delighted Cerambyx and his consorts, and Quercus likewise offers the woodpecker a great real estate opportunity: a space has appeared where a long-dead, abandoned branch has fallen at the juncture between two healthy branches. The scar has begun to be digested by microbes and other fungi.

Dendrocopos began by seeking out a forest area rich in wood-decomposing insects – saproxylic beetles make up the major part of his diet. These insects are found at various depths in wood, depending on the species – Cerambyx’s larva, for example, seek out the quiet, wellregulated thermal conditions and humidity found deep in the wood inside the heartwood of old oaks. But this doesn’t pose a problem for Dendrocopos. His tongue, more than ten centimetres long, gives him access to most decomposing insects. Another important factor is that when brooding, the female can’t leave the nest for longer than three minutes – otherwise the eggs might cool down and stop developing. That’s why it’s so important that food sources are nearby.

This forest area meets their needs. A large oak has recently died, and several holes in the crown signal the presence of beetle larva. One of them is probably Cerambyx’s offspring. It’s the perfect feeding spot – the female can avoid being too close to the ground when eating, making it less likely she’ll be caught by a predator. And this pantry is less than thirty metres from the ideal lodging Dendrocopos has found in Quercus’s branches.

There’s no risk of a terrestrial predator reaching the nest, which sits nearly eighteen metres off the ground in a scaf-fold branch. This branch grows directly out of Quercus’s trunk and separates into two almost vertical branches; it’s a secure spot. All the pair of birds need to do is clear the future nest of its already worm-eaten rotten debris. Woodpeckers often have to tackle areas of healthy wood on a tree, for lack of a sufficient supply of shelters in breaches such as this. Here, luck is on Dendrocopos’s side. The scar left by the dead branch is round. With his chisel-shaped beak, all Dendrocopos has to do is gradually detach the bits of deteriorated wood and toss them out of the cavity. Once the operation has begun, and if she approves of his choice, the female participates too. The nest cavity takes shape fairly quickly – in ten days, the work is done. Quercus has provided a perfect spot to welcome the great spotted woodpecker couple, with an entrance five centimetres in diameter and a passage ten to eleven centimetres long, leading to a snug cavity thirty centimetres deep.

In January, the birds begin to nest inside the hole. Since the space is small, the female stays in the nest while Dendrocopos must content himself with another nearby cavity, drilled years before. The mating phase begins. The female’s mating call is three rounds of drumming. They mate up to six times a day, but never for more than three seconds; their high-wire act, balanced on a branch, is precarious. Our female then lays seven eggs – an excellent result for the species. The average is between four and seven, so perhaps she is helped by the ideal living conditions; the dead wood full of food nearby, the abundant cavities, and the many mature trees offering beautiful views.

After the twelve-day incubation period, Dendrocopos helps the mother care for the hatchlings. One adult stays in the nest while the other goes out in search of food. The chicks need eight to ten beak-fulls of food per hour, from morning till night. They are insatiable! But after around twenty days, they’ll be independent, even if their parents still feed them for a few more days. Then, over the course of the summer, they’ll be chased off their parents’ territory for good.

* * *

All this raises a troubling question for the forester in me, who loves trees as much as birds: does the woodpecker damage the tree by accelerating the degradation of its wood and allowing decomposing organisms direct access to the heartwood of the trunk? The great spotted woodpecker made its home by taking advantage of a small point of weakness on Quercus. It’s clear that a branch had been there before – we can see that the bark surrounding the entrance to the nest cavity forms concentric ridges around the hole, signs that wood tissue once grew there around another structure. When it fell, it left a breach where decomposing organisms and wood-eaters could enter and weaken the tree.

Quercus must now draw on energy to defend himself and isolate the compromised area. The raw and phloem sap will continue to circulate, feeding the branches above while bypassing the damage. Quercus forms a bulge over the area, a scar composed of tissues that are particularly high in difficult-to-digest lignin. He’ll reinforce the wood around the area of attack and block the sap-conducting vessels that have become useless, though he would really prefer not to have to dedicate so many precious resources to the project.

Bearing all this in mind, the woodpecker’s intervention seems to have weakened the tree. But there’s a completely different way to look at things: the woodpecker located an existing vulnerability and helped to neutralise it by eradicating infected debris. The bird has tended to Quercus’s wound. The great spotted woodpecker may have accelerated the wood’s dismantling, but the death of the branch would inevitably have resulted in the gradual opening of a hole. And often, when a cavity like this forms and remains open, the tree is unable to close the breach fast enough before animals, fungus or bacteria begin their corrupting work. The woodpecker helped Quercus by clearing the rot. And year after year, he will continue his valuable cleaning work.

This situation prompts a question. By abandoning the dead branch, did Quercus take too great a risk? The branch was left to fall because it was not productive enough, and the tree bet on its ability to produce scar tissue fast enough to curb the ensuing corruption. It was a big risk, and the fact that it has paid off is in no small part because of the birds. Not only did they clear the debris, but the wood-peckers consume a great quantity of insects. The adults eat wood-munching saproxylic insects, while the chicks crave caterpillars like Tortrix, which can defoliate trees to the point of weakening them permanently. The woodpecker family will consume thousands of caterpillars during the month when the chicks are growing. The single brood of a much smaller bird, the great tit, which may occupy a wood-pecker’s nest after it’s empty, might also consume five to eight thousand caterpillars.

By sacrificing part of his physical integrity, Quercus has gained a considerable advantage. He has secured a cleaning service for at least the year the woodpeckers are nesting and can better keep his foliage intact. The energy he conserves supports his growth, protects him from parasitic attacks, and provides tissue reinforcement around the entrance to the nest cavity. Paradoxically, the tree has increased his overall capacity for immune response by allowing the intrusion of an animal into his own flesh.

When I observe the complex chain of events and the reciprocal benefits that have ensued, I can’t help but wonder: did Quercus somehow know what he was doing when he sacrificed the branch? Perhaps it’s far-fetched to imagine that trees can have intentions, and yet there is still so much that science does not fully understand about the manifold, ever-evolving relationships between species.

MYOTIS, THE BECHSTEIN’S BAT, 1999

In which we learn that Silva’s character changes at night, and that the nocturnal atmosphere encourages mysterious animals to emerge. We discover that bats may be the forest’s best friends, at night in any case, and that their way of life is complex; social for some and solitary for others. Myotis, the Bechstein’s bat, fights to find housing that changes location every day. Managing this is complicated.

The year is 1999.

To penetrate the mysteries of the forest, you must abide by its laws. Settle in to watch, listen and align yourself with the rhythm of the visiting animals. Become a little wild yourself. At times, an animal will pass by and catch your scent. The creature freezes, and so do you. Time stops. There’s an uncanny moment when intellect is abandoned in favour of animal instinct. Then it continues on, leaving behind an image engraved in your memory.

One of the best times to observe animals is at the end of the day when the light projects mysterious shadows in the underbrush. Fauna move cautiously through the gloom. This is my favourite time. With dusk, humidity gradually increases through moisture rising from marshland and the process of evapotranspiration. The sun’s rays graze the horizon, and twilight sets in. The temperature slowly drops. Large herbivores leave their diurnal shelter to head for the richest meadows. The absence of large predators makes them easy to observe. Woodpeckers such as Dendrocopos head back to their nest cavities. The soundscape changes. The robin lets out a last song before returning to its hidden nighttime perch, along with the other diurnal birds, for a well-deserved rest. Darkness falls, and the murmuring of Silva subsides. It’s early July, and the night promises to be rich, full of fantastical stories. The conditions are ideal for Myotis.

Bats, the animals I enthusiastically made my speciality, become masters of the nighttime forest. It’s impossible to observe them in the dark without specialist equipment – which is part of what makes them so mysterious. It took me several years to understand their relationship with the forest. To detect, in the flight of the Bechstein’s bat, the signs that reveal their essential role in its survival.

* * *

While I was embarking on the nocturnal life of a naturalist forester at the National Forestry Office, Myotis was awake at the top of Quercus, readying herself for a new night. In her interactions with Silva, Myotis is by far the forest’s best nighttime ally.

* * *

In bat colonies, the life of each female follows a set rhythm. Myotis gave birth to a single baby a few days ago. Because its fur is yet to appear, it still nestles into its mother to stay warm during the day. It doesn’t yet have the ability to thermoregulate. After two weeks, it will be able to stay alone in the roost, but in the meantime, it depends on its mother and the other adult females in the group. The Bechstein’s bat lives in a colony of several dozen individuals. Weighing only ten to twelve grams, females with strong family ties have formed a colony in the former woodpecker’s nest, a shelter that will keep them from being disturbed.

They’ve known about the hole drilled by Dendrocopos in Quercus for a few years now, and it’s the perfect spot for one of the essential phases in the group’s life: childbirth, also called parturition. In the spring, the colony changed their roosting spot nearly every day because the females were so afraid of being noticed by an owl, a dreaded predator whose habit is to wait at their roost’s exit to eat them. The daily relocation strategy is effective; the nocturnal raptor doesn’t have enough time to find the bats’ new location each night. Throughout the year, this colony of nearly two hundred bats will use about three hundred different cavities, favouring those left by great spotted woodpeckers or their cousins, middle spotted woodpeckers, as well as fissures that result from the cracking of wood fibres.

Finding three hundred different cavities can be a real challenge for the colony, so everyone lends a hand – Myotis, her sisters, and the other parents. As soon as a new cavity is found, this information is shared during the day via small cries only they can understand. Except that many of these cavities aren’t big enough to house the whole colony. Even if they’re as big as a shoebox, they can rarely contain more than fifty bats. So the colony splits up every night when they go out to find food, with each animal heading out alone into its hunting territory, before reassembling in the morning. The bats reorganise the composition of the groups that will settle into this or that tree cavity, staying close to each other so they benefit from each other’s discoveries. They communicate extensively in front of the roost when they come back from the night’s hunt, as well as inside. The next day, with the groups reorganised once again, they change their roost and this goes on, day after day.

* * *

The forest sector chosen by our colony is ideal, not just because the dead oak, standing forty metres away, is of great interest. Myotis won’t really look for prey on it, but she may search the flowers of the bramble that has flourished in the clearing left by the dead tree. She particularly loves Oedemeridae, tiny beetles whose larvae live on dead wood. They came when the oak tried, in vain, to fight, in the last moments of its life. But they only come occasionally, for a few days at a time.

There is something else that attracts Myotis to this place. The site around Quercus has the advantage of having attracted several woodpeckers. Numerous cavities have been drilled near the dead oak – a dozen or so can be counted within less than fifty metres. They drilled other cavities even further off. With this abundance of roosting spots, Myotis and all the bats in her colony have chosen this sector to live in for a while, where they could change location each day if they wish.

The colony has chosen Quercus for parturition. They will stay in the same place for several days, to stabilise both the social ties of the group and the temperature in the roost. The living wood all around the cavity, where sap still circulates, ensures a thermal buffer. They can avoid the cold snaps of spring as well as the heat of summer. During heat waves, temperatures inside cavities can be ten degrees lower than those of the ambient air. When it is cold, the presence of the adults heats the lodging, raising the temperature to over thirty degrees. So the young bats are not at risk of hypothermia. Also, the cavity bored in Quercus is very high up in the tree. Choosing a spot closer to the canopy reduces the risks to vulnerable young, and the surrounding foliage offers cover during their nocturnal forays.

The time for the hunt has arrived.

Myotis gets ready, leaving her little one with another younger female who hasn’t yet reproduced and will play the role of wetnurse for a few hours. Myotis jostles some of the others on her way to the exit, causing little audible cries of discontent. What’s her rush? There’s no danger in sight. She flings herself into the void, reaching Quercus’s canopy in a flickering, silent flight. She has completed the first step without incident.

Now she needs to find a hearty meal to make up for the energy expended nursing her baby. The little one is voracious. Myotis needs to eat several hundred insects every night. In spring, the operation was easy – she could home in on the caterpillars of a little green butterfly, descendants of Tortrix. Myotis headed for the leaves of the crown to snatch up these precious insects, rich in protein.

Her hunting technique is well-honed: she flies to the end of a branch to listen for the sound of the caterpillars chewing, then surprises them in the middle of a meal. In spring, Myotis can eat up to two hundred and fifty caterpillars per night. For the colony, this corresponds to about a million and a half green oak tortrix caterpillars devoured during the month of May. The bats’ role in controlling the population of these defoliating insects is significant.

But now, in early July, she needs to find other prey. The diversity of tree species attracts different insects. Around Quercus are other oaks, of course, but also beech trees old and young, hornbeams, birch, a few hazel trees, holly (which provides little prey) and Scots pines. The advantage of such variety is that the prey develops to the differing rhythm of each tree. Depending on the nature of the tree, whether leafy or resinous, whether hornbeam, beech or oak, the insects’ periods of emergence are spread out. So Myotis benefits from continuous food sources throughout the season. Hurrah for biodiversity.

This little corner of the forest offers excellent conditions for Myotis’s colony to reproduce in, but there’s one thing missing. As all mothers of small mammals will tell you, nursing makes you thirsty! In order to keep producing milk, she’ll need to quench her thirst before heading back to the roost. Eight hundred metres away, there’s an open and easily accessible forest pool, the Mare aux Biches where the free-grazing cattle in Silva went to drink around the time of Quercus’s birth. The distance doesn’t deter Myotis – she can fly much further. A round trip to this water source only takes her a few minutes, and then she returns to the colony to reunite with her pup and give him all the milk he needs.

One might wonder where the males are in this story. Life in the colony is reserved for females. Male bats take refuge in small territories and live as hermits, alone, far from others of their kind.

* * *

In 1999, when I began my research on the link between fauna and the forest ecosystem, I was yet to discover all the incredible bat activity I’ve just described. But it only took me one season – my first as a biologist at the National Forest Office – to get hooked on observing bats in their environment. Spotting them in the nighttime forest always sparks my curiosity.

When an official choice was made in the early 1990s to leave dead trees standing and living trees with cavities and nests throughout the forest, foresters gave themselves what is probably the most effective natural tool there is for fighting forest pests. And they didn’t have to do anything other than designate trees for conservation.

Indirectly, this measure continues to benefit Quercus today, because at least two nearby dead trees have been preserved. And Quercus himself has been preserved, in spite of the woodpecker nest cavity in his crown, which allows for the painting of a beautiful ecological picture to which Myotis and others of her kind bring new colour. Even if they fly by night, and see in shades of grey.

QUERCUS, 1999

Autumn, and the trees complete their preparations for the following spring. We understand better why their colours change and how trees shed certain essential tissues. In which Quercus, finally an adult in the prime of life, prepares for a long and successful second act. At least, that’s what we hope.

It is 1999.

After a rather hot summer, the autumn of 1999 is particularly wet. Floods occur in many parts of France in September and October. In Rambouillet, where Quercus, Fagus and the others stand, it rains all through the autumn and until the end of December, making the ground waterlogged.

Taking advantage of the humidity, fungi spring up from the earth. Forest fruits are sparse because of a frost in April that affected the tree blossoms. The oaks produce only a few acorns. In September, Silva resounded with the song of stags searching for females in the meadows bordering the forest. This is the period of reproduction for these majestic animals, and they emerge from the underbrush at twilight to bellow and join the herds of females to copulate. The cries of the stag proclaim the beginning of autumn.

In October, Quercus’s canopy began to change colour, gradually adorning him in a more sober brown. The chlorophyl of the crown becomes oriented towards the production of various tannins because, once they’ve fallen to the ground, the leaves will need to slowly break down to bring their nutrients to Quercus on time, next spring. Then the chlorophyll disappears completely because of the decrease in sunshine and length of the day. The leaves fill with anthocyanins, driving insects towards other trees that are still green.

In November, the leaves fall, a phenomenon accelerated by the first frosts. The abscission zone that links the leaf petiole to the twig has become more fragile, and hormones and enzymes eventually loosen the leaf, helped by the frost and wind. The leaves are let go, conserving the tree’s energy as it prepares to go dormant for the winter. Quercus disrobes, while the forest floor dons a multicoloured coat in shades ranging from bright yellow to dark brown, rich with the leaves from all Silva’s trees. No more evapotranspiration, no more rising of sap, no more fabrication of sugars or tissues. The forest waits for Nemobius and leaf-litter-decomposing partners to come back to life and begin the chemical and mechanical breakdown of dead leaves at the end of winter, allowing these molecules to be released towards the tree, who will pick them up with the help of Leccinum. Quercus and the other trees in the forest begin a new cycle.

* * *

The landscape of the forest has changed a great deal since the birth of Quercus, from a heath with a few tall trees and stands of hornbeam, coppiced regularly for firewood, into a very structured woodland. The diversity of dominant trees has allowed the return of numerous species that depend on mature trees. There are now several of these, and a dense underbrush. Quercus has learned to avoid as much as possible the risks to which oaks are exposed. For years, he has been opening his buds later than his neighbours in spring, limiting the attack of caterpillars like Tortrix. Each spring, he has made reserves of sugar and starch, stored them in the liber of the taproot and other roots to limit the effects of the winter freeze on the fragile sapwood, and already prepared for next season’s bud break. Because the trunk unloads sugars and all the molecules transported by the sap, as well as the water that makes up the tree’s vital fluid, Quercus’s diameter shrinks, a tiny bit. The aerial parts lose matter while the subterranean parts, from taproot to furthest filament, fill with so many reserves, his mass shifts slightly towards the base. The buds are formed and protected by a layer of wax. Quercus has barely settled down to rest after losing his leaves when he’s already ready to meet his next spring. Assuming he makes it …

… For that is not a given. The trees have used this autumn transitional phase to ready themselves for a new growing season to come, but the forest is not prepared for what’s in store.

LOTHAR AND MARTIN, ATMOSPHERIC MONSTERS, 1999

In which Silva experiences a trauma and we understand how deeply we are connected to our forests. Despite humans’ attempts to master everything that surrounds them, we begin to acknowledge our considerable impact on nature’s equilibrium. The arrival of storms Lothar and Martin is a stark wake-up call.

26th December 1999.

No one saw it coming. No one except, perhaps, the large forest animals that were spotted by drivers emerging onto the road on the night of 25th December 1999. These creatures probably detected the sudden fall in atmospheric pressure. Humans have largely lost the instinctive capacity to hear what nature is telling us. But the animals felt it. They knew disaster was heading their way, and that they couldn’t remain among the trees. Before a cataclysm, it is common for nature to freeze, with birds hiding as best as they can and forests falling silent. This is probably what happened on 25th December while indoors, oblivious, humans celebrated the festive season.

* * *

Silva has reached a new turning point in their history. In just a few hours, they are about to be transformed, with painful consequences for the whole forest community. Since the plants are in total dormancy, it’s possible their epidermic tissues don’t detect the change in atmospheric pressure. But it’s likely that all the mammals and birds of the forest feel a general panic.

* * *

And then the monster arrives. On the morning of 26th December, nature marks the end of the millennium with a show of anger. Storm Lothar hits our coasts, passing over the northern half of France in just a few hours at an exceptional speed. Winds are violent, with gusts of over a hundred and eighty kilometres an hour. At the edge of the Rambouillet forest, gusts are thought to have been even stronger. Models suggest they reached close to two hundred and thirty kilometres in some places. After crossing the great agricultural plains of La Beauce, at the forest’s edge, the mass of advancing air is blocked by the wall of trees and forced upwards, causing a deafening whirlwind to rage up to a hundred metres inside the forest.

Silva’s robust mix of large oaks and hornbeam coppice understory usually helps to ensure their stability, but in a storm of this intensity, the power of the elements prevails. All hell broke loose. Not far away, the wind took down five hundred and fifty hectares of pines in a single block, planted, like so many others, just after the Second World War. Trees are completely destroyed. One oak tree, ninety centimetres in diameter explodes, the trunk resembling nothing more than a pile of matches scattered over more than five metres.

Across the forest, three hundred thousand cubic metres of trees fall in three thousand hectares, not counting all the other broken trees scattered throughout the forest. The loss of wood is the equivalent of ten years of fuelwood harvesting. The landscape is overturned, completely altered.

* * *

Fallen trees are scattered across the valley, but Quercus still stands. During the most violent winds, his trunk bent a little but held strong, thanks to the structure of its wood, with its complex arrangement of lignin, cellulose and hemi-cellulose molecules, which makes it solid but also flexible before the raging elements. His crown was shaken and tossed, but luckily, with no leaves, there’s little for the wind to latch onto. Still, a low branch, six metres up, suffered – it was twisted violently, and the fibres begin to let go. This blow marks the start of the branch’s decline, and today it shows further weakness, with a fissure appearing at the juncture of the trunk.

* * *

Silva’s trauma brings about considerable changes. As many trees broke and fell, they brought down animals that had been hiding in cavities high up on trunks or in branches. Sleeping bats, for example, or insects in the larval stage. With the ground soaked, the roots of some trees become fragile, and one such tree falls thirty metres away from Quercus, breaking a few hornbeam and beech saplings and wounding the trunk of a large oak. Fortunately, it doesn’t take down any other trees with it – elsewhere, trees fall one after another, like rows of dominoes. Further off, in the former heath, a group of Scots pines collapses. Some trees appear to have been spared, but the wind has managed to lift them off the ground before crashing them back down to earth. Around these, fractures in the leaf litter can be seen, like faults in the earth, indicating the tree is living on borrowed time. With many of their roots broken, these trees will have trouble getting nutrients, and although they survive for a time, most won’t last through the droughts that follow, particularly that of 2003. They’ll dry out while still standing. Others will fall suddenly, without warning, perhaps on a windless day under clear blue skies. Thankfully, Quercus escapes this tragic fate, possibly because of a surplus of weight in the reserves accumulated in his roots.

During the evening of the very next day, 27th December, Martin, a storm just as intense as Lothar, begins to move across the South of France. The total damage from both storms amounts to seven per cent of all available timber at the national level, or about a hundred and forty million cubic metres of felled and broken trees.

This shocking disappearance of large areas of forest hurls us out of our comfort zone and reminds us that, for all our human arrogance, we are not fully in control of our environment – any more than we are in control of our lives. Nothing is permanent, as nature shows us – there will always be unexpected upheavals. In a time of intense global warming, which affects us all whether we like it or not, what do Lothar and Martin have to teach us?

The day after the two storms, called by many the Storms of the Century, many nature lovers began to think about the environment and our place within it. Beginning in 2000, the number of visitors to the forest multiplied. Although revealed to be fragile, the woods were a refuge, bringing humans a little closer to our forest-dwelling hunter-gatherer origins, and people were keen to feel this connection.

* * *

I remember the week after Lothar passed through. I had only been in the forestry world for a year. After clearing the roads of fallen trees and freeing houses that had been isolated, I reached my main area of study, where I had studied bats the previous summer. The state of affairs was grave, a large portion of the trees I had come to know had fallen. But even then I wondered; are storms always a catastrophe for the forest? Perhaps not entirely …

SALAMANDRA, THE FIRE SALAMANDER, 2000

In which we discover another side to Silva. The fallen trees offer shelter to many forest creatures and an unexpected opportunity for water-loving animals to reproduce. Heavy autumn rains plus the fall of a tree will increase opportunities for a certain Salamandra.

Early in the year 2000.

In the aftermath of the storms, life gradually returns to its natural course. The forest emerges from its torpor. It begins to heal, and, perhaps, to create something new. It takes only one or two days to hear the winter birds again, seeking new territories in the devastated woodland. The borders of territories are redefined, as each bird finds its place.

Salamandra is not particularly affected by all this. She can hear the birds, but her way of life is nocturnal, and competition for a territory doesn’t concern her. The fire salamander, Salamandra Salamandra, is an amphibian like a frog or toad, but with a long tail. She’s black with yellow spots on her back and around her eyes that warn predators she can secrete several neurotoxic alkaloids. Touching them can kill any predator that tries to eat her. For a few years now, her diurnal and winter refuges have multiplied – the dead branches strewn throughout the underbrush offer ideal protection for species that live on the ground. Voracious boars are less apt to rummage under dead branches, and in any case, they avoid the salamander and its poisons. Salamandra seeks out a shelter not too far from the Mare aux Biches, where she habitually reproduces.

* * *

Night has fallen. After months of gestation, the time for egg-laying has arrived. Salamandra leaves the shelter of the large oak branch lying on the leaf-litter and moves with clumsy steps towards the underbrush, swallowing a few insects that have already awoken despite the winter. On her way to the Mare aux Biches, she’s blocked by the trunk of a large oak felled by the storm, and as she searches for a way around it, she comes across the hollow formed by the stump of an oak that was uprooted beside Quercus. Salamandra is looking for a specific kind of water hole to lay her eggs – a new place, where competition is almost null, for the larva to be born. Salamandra larvae thrive in ruts caused by forest machinery, and small, newly created ponds. Mosquito larvae – also pioneers, who will make do with even a puddle – are her main prey, and she helps regulate their population. This hollow full of rainwater will be a good spot to welcome her larvae. Strangely enough for an amphibian, she can’t swim, and must be very careful to stay at the water’s edge. The problem with this type of environment is that access to the water is particularly steep. She catches herself several times so as not to fall in and risk drowning.

While Salamandra needs vegetation to hold herself up, this time she’ll make do with an outcropping root. She gives birth to embryos that are already well-formed, surrounded by a gelatinous transparent envelope that soon breaks. The young larvae will have a few months to finish their development before emerging from the water.

Once the laying process is finished, Salamandra extricates herself with difficulty from the hollow and heads back towards the forest. All she has to do now is enjoy the slow arrival of spring, and stock up on the reserves she’ll need for the next reproductive season. In the small hours, she hides under a nearby piece of dead wood. The storm has caused many branches to fall, so there’s no shortage of shelter.

The apparent catastrophe of the storm presents new opportunities. If it’s not collected, dead wood offers indispensable shelters to many ground-dwelling species. Even if people gather up many of the fallen trees, several remain in place, offering new habitats for rare species, both fauna and flora. Subsequent naturalist monitoring around Quercus and further into the forest will show that some species benefit greatly and see their populations increase, including our fire salamander.

LACERTA, THE SAND LIZARD, 2000

In which storms take us on a journey back in time, stripping former heaths of their arboreal cloaks, revealing them as they would have been in the 18th century, when Quercus was born. We observe the return of exceptional biodiversity, and realise that the job of the forester has evolved; they must take care of the new, nonnative species that are increasingly taking shelter in the forest as their own environments disappear.

The year is still 2000.

Lacerta’s habitat has been disturbed, to say the least. During the storm, he found refuge in the rootstock of a pine tree. Pine groves are not his preferred habitat, but he didn’t really have a choice: on one side was a marsh dominated by eagle ferns – a plant unsuitable for the development of entomofauna – and on the other, an old oak grove that let no light through.

In the midst of his winter sleep, the storm toppled the tree in whose rootstock he had found shelter. All the other trees around are knocked down too. But miraculously, the structure of Lacerta’s shelter was spared and it’s likely he didn’t even notice. During the spring awakening, when the first rays of sun pierce the vegetation, the root masses of uprooted trees warm up, bringing more resources to the underbrush, which is now just a few bushes and young birch shoots. With direct light, the heather, which had previously missed out on the best spots, can finally stretch out its vegetative volume and colonise this remodelled landscape. The heathland changes drastically, returning to its glory days when Quercus was born, when heather dominated the area, and only the parent tree provided a bit of diversity to the landscape.

Now that agriculture in the forest has long ceased, there is little to prevent thermophilic species – those that love heat and direct sun – from making it their home. Our sand lizard, Lacerta agilis, emerges from its winter torpor around the same time that Salamandra finishes laying her offspring and sets off in search of prey such as Nemobius, in the leaf-litter of the neighbouring underbrush.

Lacerta’s first vital instinct after hibernation is to expose himself to direct sun. He emerges from his shelter and climbs its exposed root mass. Like all reptiles, Lacerta is heterothermic. His temperature fluctuates according to the temperature of the air around him. His vital functions, in particular his digestive capacities and reproductive functions, work best when his body is around thirty degrees. If it’s too cold, he remains mostly still. If the sun is too strong, he risks overheating. He thermoregulates a metre above his burrow, because this large lizard likes to be able to see danger arriving from a distance. He performs this exercise every morning, for varying lengths of time, depending on the weather.

Once he’s ready, Lacerta begins to prospect his territory, which is limited to a few dozen metres around his shelter. First, he meets other species of reptiles, such as a few wall lizards regularly found on the sandy path, and a viviparous lizard, who lives in the marsh and underbrush around Quercus. Since these are both smaller species, they stay out of his way. Lacerta is hungry: after periods of winter rest, creatures must eat a lot to rebuild their reserves of fat. He finds a hill of large red wood ants and devours a good number, rivalling Dryocopus’s descendants. This is enough to fill him with energy. Next comes the search for a female. Last year he met an available female on his territory and mated with her. She dug into the sand to lay a dozen eggs, but the habitat was unfavourable and the couple had to cover a large radius to find food. Now, they find each other again quickly enough and, once their reproductive mission is accomplished, Lacerta climbs to a high vantage point to make sure another male can’t approach and interfere. He’s the only one around, for now, but that won’t last. In a matter of weeks, a few juvenile lizards will settle into neighbouring territories, now that so many pines have fallen, opening up the heathlands favourable to the species. Later, I’ll be involved in monitoring the lizards along with a few naturalist and forestry colleagues, and we’ll discover that the site density of this lizard is high. For the region’s lizards, it is a stroke of luck that violent winds came along to rejuvenate the area.

In the year following the storm, fallen pines begin to be harvested. The work must be done quickly because the wood on the ground is rapidly colonised by wood-decomposing insects, bark beetles in particular, whose life cycle is short. These Coleoptera emerge in large quantities; there are thousands of individuals per log. If pine logs are left for more than a year, they lose their commercial value. So they’re carried out of the forest without delay, and not replanted. The devastated area is left to evolve naturally, and heather springs up soon after. Logging machines have torn up the ground, stripping patches of bare sand, all the better for thermophilic species.

Lizards are not the only species to benefit after the storms. Two birds typical of heathlands, the common night-hawk and the lulu lark, had almost disappeared after the forest recovery that began at end of the 19th century filled in the open areas they preferred for nesting. Only logged forest plots allowed them to survive. The storms have now returned the heathland to the state it was in at the time of Quercus’s birth, in the 18th century. When the nighthawk and the lulu lark return from their African migrations, they colonise these new spaces, and their populations grow.

During the growth period of adult pines, only the pine cricket managed to live in the underbrush. Other crickets survived, with difficulty, at the forest’s edge and at the edge of the path, but in vestigial populations. The opening of new spaces prompts a reorganisation of these orthoptera insects. From one year to the next, the common pine cricket will make way for numerous other species including the blue-winged grasshopper, the bow-winged grasshopper, the woodland grasshopper and the mottled grasshopper.

Biodiversity monitoring shows the growth of these populations, but to maintain heathland species, it will be necessary to fight against the trees – which is challenging at a time when society is calling for even more wood, partly as a response to global warming, and also because the demand for wooded areas for walking is only growing. But Lacerta is sensitive to the closing in of his environment, and the growth of young birches and a few Scots pines calls into question the sustainability of his habitat.

A little further off, in another group of forest plots impacted by the storm, the pines that dominated have also been felled. Foresters had classified this area as an ecological reserve for the conservation of biodiversity. This reserve might offer a new refuge for Lacerta.

The case of Lacerta embodies a paradox for Silva: as the forest expanded in area and the trees continued to grow larger, as society has demanded for a century and a half, Silva is now being asked to be more than a forest. Foresters must compensate for the widespread disappearance of habitats essential for open-environment species, like those found in large-scale agricultural lands, which are becoming increasingly inhospitable to biodiversity. Paradoxically, this means fighting against trees in certain designated forest areas to allow Lacerta and all the heathland species to reclaim their former glory.

With this new responsibility, foresters see their profession evolving. As for Lacerta, the lizard heads towards new heathlands that will allow him to expand his territory.

HOMO AND SILVA, 2000 TO 2019

In which we consider the future of our forests, and global developments invite humans to rethink their practices, sometimes forcing foresters into conflicted positions. Tree marking begins, helping to ensure the continuity of Silva and Quercus.

First two decades of the third millennium.

The first response after the cataclysm of the storms was to clean up the forests. People had the impression that Silva had suffered, and that all the toppled trees had to be removed. It was only after the first phase of cleaning up that the forest industry reconsidered its haste to clear the dead wood.

While people were upset by the destruction, the storms turned out to be a real boon for biodiversity. The influx of dead wood helped saproxylic species, some of which had become rare but can now be found here once again. It was subsequently decided that windfall (trees felled by wind) and windthrow (trees broken by wind) should regularly be left alone to serve as refuges. In various areas throughout Silva, several hectares of deciduous trees in a single block, most of which have fallen, are left as they are. These habitats become refuges for more than thirty per cent of forest species, including thousands of insects and fungi, as well as vertebrates such as certain birds and bats. Other species who like open environments take over the larger clearings.

Lothar and Martin radically changed the way foresters understand the forest. What appear to be abandoned spaces are in fact being deliberately ignored by management. Nature takes its course.

* * *

When Quercus awakens in spring 2000, a few months after the disaster, he immediately detects an atmosphere saturated with alkaloids. Nearby oaks have suffered some damage. Some have cracked and produce covering tissue to limit parasitical intrusions. Quercus picks up the distress terpenes. An oak has fallen and tries its best to survive, but its root system is profoundly affected. Most of its connections with vital mycelia are destroyed. The trunk of a beech has broken, four metres up. For this tree, photosynthesis stops, but not necessarily its life-cycle. Wood-decomposing insects flock to devour it, prolonging its contribution to the life of the forest for a few more years. Some of them stop on other beech trees nearby, which must defend themselves.

The forest trees have so much to say to each other; Silva is practically seething, buzzing with signals, full of life. Quercus receives essential oils that inform him of the condition of his neighbours, and sometimes information travels through mycelium. But now it is the leaves that gather most of the news. Lower down, where the branch broke when Lothar blew through, the tree closes the channels that fed the branch and begins the work of covering the fissure on another branch six metres up. The work is incessant, and the photosynthesis factories operate round the clock.

* * *

The storms shook us up. What do we want from our forests? Society is full of contradictions – some people want to extract the maximum of resources, while others want to preserve as much as possible. In 2008, France organises an environmental summit in Paris that brings together representatives involved in nature protection, civil society, public authorities and industry, with the goal of reaching a consensus about our environment. At a time of global change, society is also demanding wood. Questions pile up, opinions diverge, and the summit ends with a compromise that boils down to a single principle: produce more wood while better preserving biodiversity. The measure proposed at the summit is complicated to put in place, and the climate must take precedence over biodiversity. Foresters are caught between several proverbial stools, and making the right choice is not always easy.

The storms have finally forced together the question of biodiversity with the other two pillars of forest management: wood production and recreational function. A forester once summed up his profession for me: ‘Forest management is about the art of compromise.’

After the storms, the ultimate goal is to render the forest more resilient in the face of disruptions, some of which may still be unknown. Just twenty years before Lothar and Martin, society couldn’t imagine the risk of acid rain pollution, nor the possibility that the climate would reach a tipping point.

The creation of new spaces entirely dedicated to biodiversity is proposed. Reserves had already been put in place for saproxylic biodiversity, for that of wetlands, and heaths as well, but even more are now created. Islets of a few hectares are designated where dying trees will be left to fall, and within wood production plots, trees of other species are allowed to grow because their role is essential to forest biodiversity. In Silva, all these measures must also be adapted around the fact that the public is visiting in ever-greater numbers – more than ten million people each year.

* * *

After a few years, although Silva seems to have healed, it’s time for a review. The trees have continued to grow, and some can now be harvested for timber and firewood. One autumn morning, the team of forest technicians is at work. The goal is to mark the few trees to be cut down. This operation must allow for the best possible healing of the area as well as forest renewal by leaving room for the youngest saplings, which have been patiently waiting for a space to open in the canopy. The task is to ensure continuity, to manage the forest that has been bequeathed by predecessors, and build – starting today – a forest that will respond to the issues of tomorrow. While making these improvements, the silviculturist must look a century into the future.

Silviculturists move forward through the underbrush. The marking is about to begin. The rule is to favour oaks, provided their natural regeneration is ensured, while also leaving other forest species present on the plot to encourage biodiversity and resilience. A tree might be harvested either to leave more room for others or because the plants beneath it are necessary to continue forest history. Foresters are no longer planting – instead they are relying on seedlings already there. Letting nature do its job.

One particular tree is an issue from the beginning. A large oak with two woodpecker holes is favourable to arboreal species, but leans dangerously over the sandy path. First tree, first dilemma. Just below it, tiny oak seedlings no more than a few centimetres tall can be seen poking up. Even if it offers microhabitats for arboreal species, the oak is marked for harvesting because it’s considered too dangerous for the hikers who regularly pass by on the path. The young oaks will benefit from the opening in the canopy and will take over, as Quercus once did. Further off, young pines are already well-established in the underbrush. Two oaks are limiting their growth and will be harvested to promote the future of the evergreens. Another oak shows the typical black marks of canker, a fungus that degrades the quality of the wood. Because it’s one of the rare fungi that could contaminate the surrounding oaks, this tree will also be harvested. During the process of marking, when certain trees are designated, the others around them whose shape and vitality will ensure the longevity of the stand are also examined. Each decision is carefully weighed, and less than one in five trees will be harvested.

Further on, the trunk of a tree shows a fissure, as well as polypores that betray its internal colonisation by the filaments of a fungus, such that the tree has no further commercial value besides firewood. On the other hand, it constitutes an interesting habitat for arboreal species, some of which are regulators of insect pests. This one is kept, and marked with an orange triangle, signalling its maintenance for reasons of preservation of biodiversity. Next is an opening in the canopy beneath which dead wood is now at the end of its decomposition. These are the remains of an oak that died nearly twenty years ago and attracted many saproxylic insects in the last moments of its life. In this clearing, birches a dozen metres tall dominate the beech trees that follow, in spite of the eagle ferns that take advantage of the additional light, growing taller and denser. A mature oak at the edge of the clearing has just died. It still has bark attached to its trunk. All this, along with the other oaks surrounding the clearing, is left intact. The young saplings that hungrily suck up the photons inundating the clearing are guided skyward by the surrounding adult trees. They are beautiful trees in the making. A forester draws another triangle in orange paint on the trunk of a dead oak. It’s too precious for the healthy functioning of the whole forest.

The team approaches the area where Quercus lives. Does he know what’s happening? Quercus didn’t produce acorns last year, but neither did the others of his kind. The forest manager’s actions are limited here to an analysis of the trees’ architecture and the quality of their wood, without consideration for potential seedlings. Because he is the tallest, widest and most imposing tree in the stand, Quercus presents the most potential for the future of the area. He should produce the best seeds for forest renewal, the ones with the best possible genetic resource to ensure forest continuity. One of the technicians notes that a small oak nearby is preventing the development of one of Quercus’s main branches towards the west and decides to mark it. The two beech trees with black woodpecker cavities are each given an orange triangle. These trees will last, benefiting Dryocopus’s descendants. Further south, a cluster of oak seedlings foretells possibilities of natural regeneration. Above them is a large oak with a bright future ahead. Since the light comes mainly from the south, another oak and a large beech tree will be harvested to increase lateral light for the young saplings. Future generations of silviculturists will have to evaluate whether to cut the oak tree above the saplings, which for the moment is not a problem.

Only three trees in the area surrounding Quercus are destined to be come down, while several will be saved. Quercus and most of his neighbours will remain standing. The entire site is maintained.

The foresters go on their way and continue their work in an area where hornbeams dominate the underbrush. The ambience changes. If they need removing, the branches of the hornbeams might provide firewood, which the inhabitants of the neighbouring village are keen to have. But the forester is unswayed by this concern. His actions remain consistent: looking closely at each tree and trying to make a decision in the interest of the entire forest community.

SILVA, 2019

In which Quercus shows an extraordinary ability to adapt, and Silva heals in the face of an onslaught of disturbances. Epidemics, periods of extreme drought, heat waves, floods, parasites – a slew of new phenomena challenge the forest to adapt. The problem for Quercus, Fagus and their neighbours is that these events are multiplying at an unprecedented speed. If humans want to continue to benefit from the forests, they need a plan. Is it still possible to change the course of history?

Early 2019.

Silva heals very quickly. The forest’s root connections are not impacted by the few trees that have been cut down, and those that remain standing become more dominant, continuing to share nutrients among themselves. Sometimes, a deadlooking stump will survive by tapping into the underground network and absorbing molecules from their neighbours, allowing new sprigs to shoot forth. These stems signal the promise of renewal, refreshing the coppice. For the moment, these are short stems growing from the layer of cambium below the bark, from which only a few leaves emerge. They are like the young saplings of a parent tree, except these are simply outgrowths of the same tree.

This is the magic of the plant world – sometimes it can seem to thwart death itself, even if mortality will, in the end, seize all living beings. The tree that was cut may itself have sprung from a previous shoot that emerged from a stump. Given that deciduous trees can release shoots indefinitely after they are cut, it is impossible to tell the true age of this stump. Only the tree really knows.

While continuity is part of the forest’s way, Silva is now confronted with a new wave of ecological disruption. Extreme weather events have been intensifying for a while and follow a steady pattern: it’s getting warmer and warmer. Specifically, bouts of very dry weather are becoming more common; these are sometimes long periods, during which severe heat waves stun even the underbrush, despite the shade from the canopy. These alternate with spells of very intense rain, during which the equivalent of a month’s precipitation might fall in the space of just a few hours. The ground has to be wet first in order to play its role of absorption. When it’s not prepared to receive such a large quantity of water, it’s not able to absorb it all, and this leads to flooding. Luckily for this part of the forest, the sandy soil is draining and the nearby marshland absorbs an enormous quantity of water. A little further on, though, the forest has been transformed into a lake of several hundred hectares for a week in late spring, for two consecutive years.

This saturation can have harmful consequences for Silva – the root systems are weakened by asphyxiation, before experiencing a sometimes-deadly dry period in summer. Less water falls per year on average, which is a real problem for the beech trees. Quercus, though, is robust. The oak is one of the rare species able to withstand extreme weather events. A drought of a few weeks? A flood? A heat wave? Quercus knows how to manage them.

* * *

These changes are happening in many forests. The beech withers and reduces its area of distribution, moving towards northern Europe. Spruces, major consumers of water, have weakened in recent successive periods of drought, and aren’t able to fight the infestation of bark beetles, small xylophagous insects that gorge on drought-distressed evergreens. In oak forests with sandy soil, beetle populations boom now that they don’t have to face frost in winter. The larvae survive and eat the rootlets of adult oaks, while the adults eat a few just-emerged leaves while they’re still tender. To make the first tissues, the tree must draw deeply on its reserves. Forestry colleagues have shown me oak stands that are sometimes completely dry and still standing, nearly a hundred hectares on a single plot, with no resources to feed or defend themselves.

In the face of climate change, we can expect a reaction from Silva. The forest will have to adapt to the new conditions imposed upon them. Certain developments have already been observed. Oaks have acquired this incredible ability to gamble on the tiny differences between each summit branch, to sometimes change a few individual characteristics and bet on the ones most favourable for the variable environmental conditions. This is how there are sometimes small genetic differences between branches on the same oak tree. Step by step, the colonial tree, each of whose branches almost constitutes an individual independent of the others, has learned to adapt to the changes to which it has been exposed. In the case of a heat wave, the tree’s deep root system allows it to maintain sufficient water resources in the early morning, with a change in the concentration of nutrients in the raw sap to modify the osmotic pressure and accelerate its movement through the conductive vessels leading all the way to the leaves. It can then close its stomata for the rest of the day and prevent water loss through evapotranspiration. This short period has been enough for it to synthesise a few essential molecules. It also knows how to survive the reduction in carbon dioxide, essential for the formation of sugars and other molecules necessary for the tree’s life. It does this by reducing all vegetative activities by almost seventy per cent compared to normal periods, without affecting its vital functions. Over the course of the following seasons, during which it will be subject to drought, it will most likely learn to gradually shrink the size of its stomata so as to reduce water loss via the leaves. These will then grow thicker to limit the risk of cellular lesions caused by intense heat.

The oak is tolerant of water stress, able to be patient and take its time improving its internal structure to better survive the changing conditions. Other species have developed different strategies, such as birch trees, which lose all their leaves in drought conditions, risking reducing their reserves for the next bud break. However, for all trees, the lack of water means a deceleration in growth. No water means less photosynthesis and fewer sugars needed for tissue fabrication. And, although the physiology of oaks may help their survival, changes in some forests are happening too fast for them to react. So in many forests, we see trees of all species dying.

What’s most surprising is the behaviour differences between trees of the same species, even when they are side by side. Quercus is budding now, two or three weeks after his direct neighbours, probably to limit the attack of caterpillars in spring. The leaves of some branches are coming out faster than others, though – on the very same tree. These observations suggest that some trees will manage, come what may, to adapt over time to changing conditions, from parasites, to drought and wildfires. Trees don’t have a choice – animals can run away from danger, but plants are anchored and have no option other than to modify their reactions if they want to survive.

A few questions remain. One is about the relationship between the production of seeds and the density of micro-mammals. When Quercus was born, his parent tree enjoyed a warmer April than that of the previous year, with average temperatures above eleven degrees. These meteorological conditions stimulate the oaks, and set off the manufacture of acorns. If climate change involves a rise in spring temperatures year after year, as certain models suggest, this should encourage Quercus and the other oaks to produce acorns every year – which would bring two risks. First, the tree’s reserves could become depleted. The second risk relates to species likely to cause harm. If the density of acorns is maintained at a high level for several years in a row, the descendants of Apodemus could see their population maintained year after year at very high numbers. It’s simple maths: if there are constantly field mice in the area taking advantage of a reliable food source, they’ll consume all the seeds without ever suffering the usual demographic collapse normally brought on by lean years. What new pattern will the acorns follow now, if the Aprils to come are warmer each year?

Another issue concerns the capacity of trees to grow. Increased carbon dioxide emissions have often been used to predict that the forest will produce a greater quantity of wood. The harvesting of wood is on the rise. This hypothesis of growth may have been true at one time, but the rainfall pattern has changed things. If we look again at how photosynthesis works, water is required to bond with carbon dioxide from the air to make sugars, starch, tannins, wood and various other molecules. But models have predicted a likely reduction in precipitation. In just a few years, climate change has already proved them right. Researchers have recently shown that trees are struggling to grow in diameter.

Even if oaks are able to live economically, how will the rest of Silva’s trees react to the lean times ahead? The questions pile up, and it’s not easy to imagine what the forest of tomorrow will look like. But we can take comfort in the knowledge that this isn’t the first time the forest has faced a challenge. We thought our forests would disappear with acid rain. But they’re still standing. Trees that live in a community make up a super-organism whose powers are immeasurable. Each increases the likelihood of the survival of the whole. And this is how Silva displays a surprising capacity for resilience, thanks to the mutual assistance which the trees can demonstrate, by warning each other of dangers, or even by exchanging defence molecules or sugars via their root systems. If Fagus was once in competition with Quercus for access to resources and light, it may well be that these two are now supporting each other. The ever-adaptable forest might one day have a whole new face. But it should be clear to us all: this does not mean we can stop looking for ways to counter global warming.

CONVERSATION WITH QUERCUS, 2020

In which it’s time to return to Quercus, after a separation that was short for him, but felt interminable on a human scale. The connection between Homo and Quercus allows us to better understand all the events that have marked the life of this magnificent oak, and leads us to a realisation: learning to observe and honour nature will help us to grow.

The year is 2020, and Quercus is two hundred and forty years old.

On this spring morning, the birds are trilling to mark their territory. There are all kinds – a finch here, a group of tits there, bickering away. In the foliage, two common chiffchaffs answer each other in their characteristic song, alternating between a high note and a lower one. Eurasian nuthatches sing their invigorating song to mark their new home, a woodpecker cavity they claimed when its previous occupant departed. They’ve narrowed the entryway with a mix of earth and saliva; it’s now just a centimetre wide, too small for many intruders. A mistle thrush dominates at the top of a far off tree, while a blackcap settles into a bush between the sandy path and Quercus. A low ray of warm sun pierces the multitude of hornbeam leaves in the underbrush and illuminates the base of the oak, inviting observers to meditate there.

* * *

I’m happy to be back with Quercus after a short period of forest fasting. All humans had been in lockdown. If Quercus could understand, he would certainly meditate on the origins of the COVID virus, that has been so devastating to humans, yet was created by human ignorance of balance and natural cycles, and he would probably question our collective reaction. Rooted as they are, Quercus and all the trees in Silva can’t get up and move. They rely on collective strategies against threats, helping one another across species boundaries – sometimes competing but still uniting to overcome difficulties. But we humans choose to stay in one place, hiding away, isolating ourselves, despite our social, nomadic nature. The trees, immobile, adapt to each shift, each new threat, and evolve with their surroundings. Some individuals die, but as a whole they survive, continue their lives and become part of history. Death is natural, it’s part of the cycle. The death of one tree is not experienced by Silva as a tragedy, because the parts that make up this organism return to Silva, helping to strengthen the others. Even its suffering helps to enrich the immune response of its neighbours. This tree still stands, in gradual decay, giving parts of itself to nourish the lives of others until its slow decomposition is complete. A single life, for many others.

Humankind, on the other hand, now resists co-evolution with the microbes that have shaped us into our species, consciously risking gradual decline in our collective immunity through isolation and excessive sterilisation.

We understand the need to care for each individual (it is, by the way, this societal awareness that has gradually distinguished us from other animal species), but it may be dangerous to try and circumvent the laws of nature. No matter what we do, we are subject to them. The proof lies in our failed attempts to mitigate the effects of global changes. We pride ourselves on our society’s ability to control nature, but then a slew of phenomena beyond our control – recurring heatwaves, floods, wildfires that consume hundreds of thousands of acres of forest each year, global warming – reminds us of our powerlessness. It is by taking steps to limit greenhouse gas emissions upstream, not trying to control the consequences, that we can slow ongoing changes. Let’s face it, we depend on nature and our animal condition, even as we set ourselves apart from other species. Time passes, the planet evolves. The story of Silva is historical proof: the current landscape is vastly different from those of the past, and likely from those of the future.

* * *

Meanwhile, Quercus, like Fagus and other neighbours, has benefited from this period. For the first time in decades, for a few weeks Quercus saw a remarkable drop in air pollution. Human activity was almost nonexistent, and as a result, many animals returned to ramble around his roots. Birds, strangely enough, sang more quietly in the cities. They no longer needed to raise their voices above the noise of engines. Although that March at the beginning of a global lockdown was the hottest on record, proof of a shifting climate, the clearer atmosphere allowed more light to pass through. The sky was a deeper, more intense blue, and at night, the stars shone brighter than ever. Silva could breathe. Silva had once again become a haven for the wild, free of humans; animals could be seen everywhere, even along the forest paths, with their small, vulnerable young.

* * *

Once lockdown was over, and during the years since, human activity bounded back to the forest. I come here now to see how Quercus is doing. Once again, he must be in full production mode, making sugars, various chemical substances and wood, while remaining alert for signals from neighbours. This is how I interpret the tree’s daily activity. I know it’s more complex than that, but it’s hard to imagine exactly all that’s going on. What I do know is that I’m bathing in air saturated with the molecules he and his neighbours produce, even if they are invisible. Sometimes a ray of sun reveals a few motes in the air – the chance to see plainly that the forest really does produce particles from trees or rising up from the ground. I’m breathing them in, every minute. Without being especially adept at shinrin yoku, life-saving forest baths, I know on a deep level that this moment in the middle of the woods brings me a sense of well-being, a form of serenity difficult to attain elsewhere. I can be myself here, fully, anchored in the present moment, because Quercus, Fagus and all their neighbours are patient observers who do not judge. They are simply there. They tower over me without imposing their presence – they leave the forest walker alone. I may seem insignificant, but that’s not the impression they give. Here, I feel part of the community that surrounds me. And this brings a deep sense of peace.

While I’m visiting my old companion, I am immersed in a world rich in sensation, colour, scent and gentle sounds. I watch the birds as I lean against Quercus’s trunk, aware of treading on his roots and contributing, in spite of myself, to the compaction of the soil that nourishes him, and I’m truly sorry for it. I raise my head towards his crown as though to ask forgiveness. His foliage dominates the canopy. I can make out each part of his architecture, the relationships between his branches, and with neighbouring oaks as well. The woodpecker’s cavity. Quercus’s trunk, which rises towards the sky. My feet feel anchored to the ground, just like his roots … I feel our connection.

* * *

Have you ever felt a bond with another being so entirely different from you? It’s as though we understand each other without speaking in words, without even having specific thoughts. But he is there, beside me. People move past me in slow motion, I can’t hear the birdsong anymore, but as one small bird hovers in front of me, I can clearly make out the movement of its wings and see exactly how it flies. I have said that trees are far more complex than they appear. Here, now, I grasp every detail, and see Quercus as an elegant mechanism with a dedicated place for each component, including me.

All at once, I understand … I understand Silva. I recognise that everything that happens in this forest – the chemical messages, the physiological reactions and the ecological relationships – happens at exactly the same time as everything else. The human tendency to classify and compartmentalise the components of forest life, to see it in ‘chapters’, masks the fact that for a tree, stimuli are numerous and constant. Quercus is sensitive to everything, eternally scanning and interpreting his environment, experiencing all of it in an interwoven way.

All of this occurs to me simultaneously.

The descendants of Nemobius the cricket and other fauna of the soil that recycle dead leaves echo all around me. Earthworms, springtails and bacteria all contribute. In the same moment, some of the molecules that were previously broken down become essential nutrients for Quercus. Beneath my feet, Leccinum the fungus gets to work chartering a cargo of trace elements freshly liberated from tannin bonds by Nemobius and his crew, along with water, which is essential for the tree. They’re just reaching Quercus’s rootlets; deep down, the hyphae are already importing new water molecules.

At exactly the same second, an Apodemus female gives birth to a litter of five mice. Some will be eaten by tawny owls and foxes as soon as they slip out of their burrows. These predators are essential to the functioning of the forest ecosystem – the regulation of the mouse population will allow Quercus to produce more acorns than the rodents can consume. Further off, a lesser white-toothed shrew catches a worm before it’s able to form an amalgam of earth and nutrients partly assimilable by Leccinum, continuing the work of Nemobius.

The raw sap climbs quickly at a speed of two centimetres per minute in Quercus’s xylem, supported by the capillarity of the vessels and the evapotranspiration that sucks up fluids from the soil all the way to the canopy. While these molecules are still in the trunk, others have just arrived in the leaves. Each root apex pumps nutrients and water chartered by Leccinum.

A hundred metres away, a sand lizard is already taking advantage of the recent opening of the heathland. There’s an abundance of flowers, and the pollinators are all abuzz. The lizard gleans a few, gulping them down. The wild bees make new reserves and then pollinate Quercus’s remaining active flowers, bringing their loot back to nests dug in the sandy soil. In the same moment, a new generation of larva replaces Salamandra. This time, they must content themselves with the Mare aux Biches, since the hollows near uprooted trees no longer fill with water, a result of successive droughts.

A couple of blue tits have set up their nest in a wood-pecker hole across from Quercus. Because of warmer temperatures at the start of the year, Quercus budded earlier than previously, at the risk of falling prey to the first defoliators. But the two birds come and go between my oak and their nest, bringing descendants of Tortrix the caterpillar to their hungry offspring. In three weeks, these chicks will have eaten between five and eight thousand caterpillars during the nesting period. The tits carry on their cleaning service, having already plucked a good many from Quercus last night. Their collective action mitigates the tree’s defoliation, and the effect is visible when I look up at the crown: there are only a few gaps in the foliage. I think to myself; even if the tortrix do weaken Quercus, they remain essential to the healthy functioning of the whole, and are vital for the survival of the tits and bats when the tree most needs them – thus, indirectly, they ultimately contribute to Quercus’s survival as well. In ecology, sometimes you must cause harm in order to do good.

The colony of Bechstein’s bats have moved into another nearby oak. A different colony – of brown long-eared bats, who eat moths and weigh eight grams each – has taken up residence for a few days in the woodpecker hole, eighteen metres up. If I listen closely, I can just make out their faint cries.

All the while, Quercus is producing sugars and various glucose-based polymers. Exactly in the same moment, stem cells in the tree’s phloem have gathered other molecules, fabricated a little earlier in the leaves, to make new sap-conducting vessels, and bind lignin to cellulose with the help of several hemicellulose molecules. Quercus makes his springtime rings in this way, and they are signals of vitality. He has a perfect proprioception, which is to say he has a total sense of himself and the elements that make up his being. His various receptors, from roots to leaves to bark, are alert. His consciousness is not centralised, but it is spread between the different parts that make up the whole.

The forest whispers. If all its sounds were audible to human ears, if we had the capacity to understand the meaning of this plant language, we would be overcome by the monumental volume of communication happening at this very moment between the trees. While I see nothing, and only catch a few of the events occurring, Quercus communicates nonstop with his neighbours. The chemical hubbub is incessant, the air and soil saturated with chatty molecules. These exchanges go far beyond the barriers of species; Quercus listens to Fagus, Pinus and many others.

A little further away, a beech tree at the edge of the remaining pine grove is showing signs of weakness. The rising temperatures these past summers, with direct sun falling on the trunk and the widespread lack of water, are getting the better of it. Xylophagous insects that feed on beech trees begin to arrive. The struggle promises to be tricky, and the tree seems to be losing the battle. Quercus detects some of its distress molecules. The stomata of his leaves are completely open, poised to catch and interpret the messages circulating in the air, and to enable the gaseous exchanges of photosynthesis. He is releasing oxygen and water vapour, but not enough to support the withering beech.

However, the ailing tree gets some respite from the community. The mycelia of various fungi are connected to other trees, beeches, hornbeams, oaks and hazels, and they unconsciously send it a few sugars to sustain it a little longer. Without knowing it, I can feel the positive effects of this crisis, in which each tree is at once spectator and actor, and I even receive various beneficial molecules. The underbrush is beautifully cool on this sunny morning, not only due to the shade but also because of the water molecules released into the atmosphere.

It is taking the tits and the bats some time to get rid of the green oak tortrix and other defoliators, and so Quercus quickly moves to produce a few terpenes. He also increases the production of indigestible tannins. The defoliators are losing, and Quercus, in his prime, still a young oak on the scale of biological time, is winning the battle on all fronts. Because yes, at his two hundred and forty years of age, Quercus is probably only in the first third of his theoretical life. Other individuals of his species reach six hundred, eight hundred, even a thousand years in some European forests. So why not Quercus?

To make a point and further discourage the attackers, he emits more volatile particles. His neighbours and the rest of his foliage pick up on these, and the production of defence molecules is accelerated everywhere. These phytoncides spread through the air and I pick up some of them, too. My immune system is stimulated, and without knowing, I produce an excess of killer cells, NK lymphocytes. If any germs try to attack me in the near future, I’m ready to fight them off.

The leaves that have been nibbled must be repaired, and they produce negative ions to stimulate cellular growth. I benefit from these too, and my cardio-ventilatory rhythm slows. My stress levels naturally lower, and my cortisol levels plummet. I don’t know how to precisely identify this stress hormone, but I clearly feel the effects of its disappearance. Just an hour of walking in the forest can reduce my stress for several days.

Finally, an unexpected event occurs. One hundred and fifty years after the last individual was culled in Rambouillet, a solitary wolf has loped in from the forest’s southern edge, after a long and gradual return to French territory. The wolf is on a long journey and doesn’t stop, despite the high density of herbivores. It continues on its way, but its passage signals the likely return, in the near future, of even wilder nature in this forest. Silva asks but one thing: that each organism with a function in its ecosystem be able to fulfil its role. They call out for the return of Canis.

* * *

In the moment when all these events are happening, it’s as though time has stopped. Quercus invites me to observe my surroundings, to meditate on the very essence of our relationships with other species, and on the role we give nature in our own lives. Quercus is a reminder of the art of living together. And my moment of epiphany in the forest is the kernel of a profound life lesson. In the forest, all is shared, all is recycled, and mutual aid goes far beyond the species barrier. For Quercus and his neighbours, what’s being cultivated is collaboration despite competition. Quercus needs Fagus, and they both need Leccinum, who also needs them. Dencrocopos the woodpecker needed Quercus to bore its hole, which Myotis also needed. Quercus benefits from both these animals clearing the tree of all attackers. Thus, all these individuals of different species participate in a complex equilibrium, at the heart of which is this elaborate communal life. By contrast, how simple it should be for human beings, who are just one species, to act together for the common good.

It is almost time for me to leave Quercus. I cast one last glance at his crown, high above me. I have the sense that we have had a long, strange conversation, one in which he has opened himself to me and I’ve been able to read the story of his life. Ever since I was a boy I thought I was the one to discover him, but I suddenly wonder: What if it was in fact he who adopted me?

* * *

On the sandy path towards home, I imagine future generations walking through this forest, and Quercus imparting to them a sense of well-being, a feeling so powerful that it prompts them to stop, look up at this magnificent tree and offer their respect. Will those humans strike up a conversation with Quercus, too?

ACKNOWLEDGEMENTS

This book tells a story – the story of a tree, a forest and their inhabitants. It also tells another story, made up of men, women and incredibly rich exchanges. Among those who helped bring this story into being are people whose presence has kept me rooted, who nourished me and allowed me to develop values, concepts and opportunities. A bit like a tree, they make up a trunk, roots and the branches of a crown.

First and foremost, thanks to Stéphane Durand for his trust, his kindness, and all the help he gave in bringing this book to life. Thanks to Aïté Bresson for her exceptional proofreading and suggestions, which contributed greatly to the improvement of the text. My thanks to the whole team who supported this project. Thanks also to Véro, an early reader who knows how to challenge me, and who shed new light on the initial project.

Most of what I’ve learned about the forest has come from colleagues and friends – first, Jean-Luc Témoin, who has patiently been trying to explain to me what a forest is for over twenty years. Others have shared their knowledge of forestry over a long period – Fred, Thierry, Sébastien, Franck, Guy, Damien, Rose-Marie, Benoît, Franck, Pierre, Gwénaël, Stéphan, Alice, Sylvain, Éric – all foresters, and naturalists as well. Others whose expertise relates to forest biodiversity include Thierry, Cédric, Serge, Stéphane, Thomas, Olivier, Jean-Christophe, Stéphane, Sandrine, Bruno, Dominique, Gérald, Pascal, Jérémy, Fabrice, and Fabien. And those who do essential work to ensure the link between the forest’s many species, and between the forest and society: Thomas, Christophe, Christèle, Patrice, Dominique and Sophie. All contribute greatly to a better consideration of biodiversity in forest management. My gratitude to you all for the countless exchanges, and for your friendship.

I also called on scientists several times to build a database of understanding. I’d like to thank Christophe, Éric, Aurélien, Frédéric, Luc, Éric, Stéphane and many others. Thank you for the precise information you gave me, and for your deep knowledge of the sometimes counter-intuitive interactions between species.

Thank you to all these foresters who work passionately in support of our forests. Their task is a difficult one, but their professionalism gives the forests of tomorrow a chance.

My deep thanks to Hélène and Sarah for their patience. Like stakes at the beginning of a tree’s life, they have supported me every day.

Finally, I have to thank Quercus, of course, and Silva, who continue to nourish me. Thank you for the ongoing conversation.

TRANSLATOR’S NOTE

Being among the trees is, so often, all I want. I grew up bounded by the concrete of this city I have left and returned to many times, but I always had my places to touch the earth. Scraps of urban wilderness. The nearby park that was large enough to have winding forest paths where I could feel lost in the best ways. Now that I am a mother, raising my twins in the same city, I feel an urgency for my children to know the peace of the woods. We take trips to a valley a couple of hours away. We practise going through ‘the doors of the forest’, as they called it when they were three. In autumn, we gather leaves in that same park and dip them in beeswax to string them up on our walls. When the gardens beside the skating rink are torn up by construction, I rescue a small tree with mangled roots and carry it home to plant in our backyard. We’re not sure it will survive. But come June, small white flowers begin to bloom. We recognise the northern catalpa. Being an Oak was a book I had to translate.

Laurent Tillon’s exquisite attention to the forest is an exhalation, inspiring and restoring. In a global moment of such frantic acceleration and distraction – a deadly combination – and, on a personal level, in a midlife moment when time’s fleetingness jolts me awake, this book is an invitation into a slower, rooted rhythm. We all need the time of trees.

Each forest being, from Tortrix the caterpillar to the book’s central character, Quercus the oak, is an entity worthy of attention. And as Mary Oliver famously said: ‘Attention is the beginning of devotion.’ Laurent Tillon devotes himself to the many entities of the Rambouillet forest, and in centring the lives of the more-than-human world, he joins the voices of authors such as Sophie Strand or David Abram, who encourage us to see beyond a human hierarchy and to remember the interconnectedness of all life.

Language deeply influences the ways we relate to the beings around us. Many indigenous languages, such as Ojibwe, Potawatomi, Dene and Lakota, as author Robin Wall Kimmerer and others have eloquently shown, are verbbased instead of noun-based and embody a relational world view. These languages distinguish between animate and inanimate, rather than between human and non-human. A tree would never be called ‘it’, much the same way a beloved auntie would never be called ‘it’. What would it feel like to think and move through the world with a language that holds process and relationships as central?

French and English are both noun-centric languages, with subjects and objects in hierarchical relationship to each other. French, however, with its gendering of nouns, lends itself well to giving each forest entity an intrinsic character. For example, la forêt, ‘the forest’, is feminine and le chêne, ‘the oak’, is masculine. English requires a conscious effort. With personal pronouns he, she and they generally reserved for humans, Tillon’s arbre-compagnon, his tree companion, would, in translation, become ‘it’. But how distancing that would feel! Using personal pronouns for the plants and animals and stones around us – such a seemingly small change – can shift our whole relationship to nature, of which we so often forget we are a part. And so, in my translation, Quercus the oak becomes he/him, Myotis the bat she/her, Silva, the plural or nonbinary being who is the forest, they/ them, and so on.