Symbiosis with Quercus Petraea :Review of Being an Oak – Life as a Tree by Laurent Tillon

In an era where our connection to the natural world is often mediated by screens, Laurent Tillon invites us to slow down and look upwards. As the head of biodiversity at France’s National Forestry Office, Tillon is uniquely positioned to bridge the gap between hard science and arboreal romance. In his new book, Being An Oak (Ithaka Press, 2025), he uses a single, majestic sessile oak tree as a representative of biospheres around the world. Through this singular lens, he crafts a story grounded in ecology and conservation, conveying nuggets of wisdom that offer a blueprint for sustainable human existence in harmony with nature.

Structured narratively like a biography, Being an Oak is composed of short, digestible chapters arranged chronologically from 1780 to 2020. It chronicles the life of an existing oak tree—christened ‘Quercus’ by Tillon after the genus name—which has thus far witnessed over 240 European summers. The author uses his own beautiful sketches of leaves, wildlife, and the ecosystem to transport readers in space and time to the French forest in which Quercus stands. This is a rich account of arboreal metabolism and a detailed exposition of a complex temperate-forest ecosystem with its myriad symbiotic interrelationships. 

The Perilous Journey of a Chosen Acorn

Biodiversity is currently under threat globally, a crisis addressed by the United Nations’ Sustainable Development Goals (SDGs), specifically Life Below Water (#14) and Life on Land (#15). Just as the value of water is not known till the well runs dry, the worth of floral and faunal species is often realised only after they have vanished. However, the interconnectedness of all life in the forest—and its usefulness to humankind—is now being appreciated by more people. Tillon’s book promises to play a key role in spreading this vital awareness.

The story begins in the late 18th century with Quercus-as-acorn. Formed by wind-aided pollination—a process where the oak trusts the air currents more than insects—he crosses the first barrier when he escapes the drilling of weevils and drops to the forest floor. Here, Tillon paints a vivid picture of the sheer odds against survival. For every million acorns dropped, only a handful will ever become mature trees. He does not know that many more hurdles await before striking root.

Tillon succeeds in making readers imagine Baby-Quercus as a determined ‘doer’, distinct from the passive backdrop of the woods. He navigates a landscape teeming with hungry creatures—pigs, boars, mice, and caterpillars—all of which cross his path. The forest floor is described not just as a nursery, but as a battlefield of consumption and energy transfer. Thanks to providential protection, Baby-Quercus exhibits resilience and endurance to bide his time during the harsh winter months, waiting patiently for the right moment to sprout. It is a powerful message of resilience for any reader facing their own struggles: patience is often the most active form of survival.

Petraea Rises: The Science of Growth

In this section, Tillon dives deep into the botany of survival. He meticulously describes the development of the radicle into the taproot and the secondary rootlets. He details the frantic, unseen ‘prospecting’ for water and nutrients deep in the soil, and the plantlet’s rise seeking sunlight. He remarks that these are wonders which often go unappreciated by the casual hiker. He mulls over whether Quercus would have felt ‘exalted’ on ‘tasting the first photons’ from sunlight through his first set of leaves, attempting to adopt an ‘arborocentric’ perspective. This shift in viewpoint is one of the book's greatest strengths, asking us to imagine the chemical thrill of photosynthesis.

The mutualistic symbiosis between the sugar-seeking fungus Leccinum and young Quercus, who is in search of trace elements, is a standout chapter. Tillon explains the formation of ectomycorrhiza (a fungus-Quercus combo) not just as a biological function, but as a sophisticated trading pact. It reads like a story of diplomacy and serendipity. Tillon considers the subterranean mycorrhizal network linking trees through mycelia to be a complex communication system far superior to the internet we humans take pride in. Through these fungal threads, trees can share resources and warnings, creating a community that is stronger together.

Along the way, he refers to antagonists like the ‘odious’ fungi oidium, powdery mildew, defoliators, and parasites which are bound to appear in Quercus’s life. Quercus’s surname, Petraea, means ‘strong as a rock’ in Latin. This speaks volumes for the sessile oak’s dogged resistance to various tormenters in nature—birds, beasts, insects, parasites, weather, and wildfires. Yet, as the narrative progresses, it becomes clear that the most significant threat comes from humans—an entity with the power to dominate nature but also the potential to become its greatest ally.

A Witness to History

Quercus’s survival is not merely a matter of biology, but of history. Through a silvicultural decision made by Napoleon Bonaparte, who needed strong timber for a future navy, Quercus is spared the axe and starts his ascent.  While Napoleon’s empire eventually fell, his forestry policies inadvertently allowed this giant to gain height, girth, and depth.

Tillon dwells on Quercus’s biological inner workings—phloem, xylem, heartwood, and cambium. Readers with an affinity for botany will delight in this lucid account of arboreal metabolism. We learn that the engine of Quercus’s production—thousands of simple-yet-complex leaves—accounts for just 2% of the total biomass of the oak. By highlighting the role Quercus plays in the hydrological cycle, Tillon reinforces the need for afforestation to combat future water scarcity. He explains how trees act as great water columns, connecting the deep earth to the atmosphere, transpiring moisture that eventually forms clouds—a vital service in our warming world.

The Web of Life: Commensalism and Chaos

Symbiosis includes parasitism and commensalism as well as mutualism. Tillon takes us through the life-cycle of the voracious green oak caterpillar. While it initially comes across as a leaf-eating parasite, it is revealed that it recirculates nutrients (nitrogen and phosphorus) derived from Quercus’s leaves through its droppings, back to the oak through the decomposers in the soil. This is a fascinating form of commensalism where the apparent damage leads to long-term soil enrichment.

Similarly, wolves feeding on herbivores (including wood-mice) increase the probability that an acorn will become an oak by reducing predation pressure. Just as the wolves unintentionally aid Quercus, the oak tree offers refuge to lichens, ants, beetles, and spiders on the outer surface of its hard bark. It serves as a reminder that no tree is an island; it is a hub of life.

Tillon also writes about the spangle gall wasp, Neuroterus, which deceives Quercus much like cuckoos lay their eggs in unsuspecting crows’ nests. Meanwhile, ‘freeloading’ owls and wood doves wait for woodpeckers to bore holes in tree trunks before rushing in to occupy them. These myriad interactions underscore that decomposers and scavengers are indispensable for a functioning forest ecosystem. Without the breaking down of the old, the new cannot rise.

Quercus’s Swiss Army Knife

Tillon uses the metaphor of a Swiss army knife to describe the defences Quercus develops to protect himself. Learning on the go, adapting intelligently, and sharing resources with his neighbours, the tree fights on—weakened often but never defeated. He fulfils his life’s mission of providing ecosystem services to a wide spectrum of biological entities, including humans. Crucially, this includes soaking up carbon dioxide from the air and helping us rein in global warming.

The tree’s arsenal includes tannins as ‘insect-repellents’, ‘sunscreens’ to protect leaves, and ‘insulators’ in the bark. Tillon also discusses alkaloids to deter caterpillars and starch reserves to be called upon during harsh winters. Intriguingly, the author touches upon the potential physiological benefits of trees on humans. He suggests that the forest environment—rich in oxygen and phytoncides—may help inhibit cortisol production in humans, reinforcing the well-documented calming effect of nature known as shinrin-yoku or forest bathing.

Historically, forests have been at the mercy of humans—exploited for economic and industrial needs. The author pays homage to the French philosopher Jean-Jacques Rousseau, whose philosophy throws light on the intrinsic value of sylvan surroundings. Tillon also details how ‘pioneer’ resinous pine trees—conifers which survive on little—play a big part in regenerating Quercus’s forest after a fire, acting as the first wave of healing for a scarred landscape.

Post-War Quercus and the Anthropocene

Quercus witnesses both World Wars yet feels fortunate to be growing old in peace. He silently watches oaks, birches, beeches, and pines being felled by advanced chainsaws as the manual axes of the past give way to industrial mechanization. He observes the emergence of forest management societies and national conservation laws. He takes delight in a welcome improvement in the biodiversity of his forest, with a return of bird species like the woodpecker and the owl.

However, Quercus also senses that the air is increasingly polluted by the anthroposphere, and the forest soil is becoming acidified.  He lives through devastating cyclones, droughts, epidemics, floods, and heat waves—unmistakable symptoms of climate change. Tillon describes the physiological stress of these events: the cavitation of water columns inside the trunk during droughts and the struggle to maintain leaf turgor in soaring temperatures. Tillon observes that each tree in the ever-adaptable forest increases the likelihood of survival of the whole, but questions how much more the forest can endure.

For Tillon, it was Quercus who provided the ‘sign’ he had been praying for as a teenager to help him see his purpose in life—a purpose linked to the forests of France, and by extension, global flora and fauna. His devotion to his calling, as a scientist and a romanticist, makes him wonder if biomimicry—or ‘arboromimicry’—can inspire humankind to unite and overcome challenges. He suggests that if human society operated more like a forest—cooperative, efficient, and cyclical—we might find our way out of our current ecological impasse.

Make it O(a)K for Mother Nature

Being an Oak is a product of the vivid imagination of a nature-loving ecologist who recreates the life of an oak tree by blending scientific theory with storytelling. The narrative is compellingly convincing. After reading this book, I am much more convinced that trees are ‘personalities’ in themselves. Translator Jessica Moore’s rendition in English deserves great acclaim for capturing the poetic nuance of the original French.

I urge you to read Being an Oak not just with your intellect, but with your heart. As author Ben Rawlance notes, ‘you will not look at a tree the same way again.’ Seek out arboreal companions in your urban jungles, protect them, and appreciate their service. If you do not find any, join with like-minded brethren to cultivate some. Jean-Jacques Rousseau, John Muir, and Henry David Thoreau would be mighty pleased.

Acknowledgements: This review is dedicated to the fond memory of my wife Varshita, who found strength and peace by spending time in forests, on riverbanks, and by the lakes and fjords in Norway and Sweden.