A forester scrapes at an old beech stump with a knife, in a communal forest in the Eifel. The stump is wide, between 1.2 and 1.5 metres across, and the tree that once stood on it was felled four or five centuries ago. Under the surface, the wood is green. Chlorophyll, and therefore life, in a stump that has not had a leaf for four hundred years. A trunk without a crown cannot photosynthesise anything, so it cannot feed itself. The conclusion Wohlleben draws from this opens his book: the surrounding beeches are keeping this stump alive, they send it a sugar solution through the roots and through the network of fungi that links them. He compares this behaviour to that of elephants, who are reluctant to abandon their dead.
That is the way into The Hidden Life of Trees, which came out in German in 2015 and was translated into French by Corinne Tresca as La Vie secrète des arbres, published by Les Arènes in March 2017. Two hundred and seventy-two pages, and a publishing war machine: 320,000 copies sold in Germany by January 2016, more than a million worldwide, thirty-two languages, 250,000 readers in France.
Thirty-six chapters, no sections
The book has no visible architecture. It strings together thirty-six short chapters, five to eight pages each, self-contained, which can be read in any order. Friendships, tree language, social security, love, school, hibernation, burnout, street kids, immigrants: the titles themselves announce the stance.
The overall movement goes from the social to the political. The first ten chapters describe the bonds between trees. The belly of the book deals with physiology and ecosystem functions, water rising, carbon storage, the forest as a pump. The final third changes tone and describes the pathologies of the human-managed forest, ending in advocacy. The English edition adds a foreword by Tim Flannery and an afterword by the researcher Suzanne Simard, whose work Wohlleben draws on directly.
What he recounts
The material is first of all that of a man who works in the field, and that is what gives the book its flavour. Wohlleben is not a researcher. He joined the state forestry service in 1987, after the forestry school at Rottenburg am Neckar, and since 2006 he has managed the 1,200 hectares of the communal forest of Hümmel, a village in Rhineland-Palatinate an hour from Cologne. In 2002 he opened a forest cemetery there, where urns are buried at the foot of two-hundred-year-old trees, which brings in money without anything being cut. Four years later, the municipality broke with the regional administration and hired him directly. He removed the insecticides, replaced the heavy machinery with logging horses, let the beech wood go wild. In two years, the forest went from deficit to profit.
The scenes he reports come from patient observation. Standing before two enormous beeches pressed together, he points out that their main branches lean away from each other, as if to avoid stealing each other’s light, while their roots are fused. He adds that if one of the two dies, the other often follows soon after. He puts it this way to a journalist from the Smithsonian: “These two are old friends. They are very considerate in sharing the sunlight, and their root systems are closely connected.”
The rest comes from published work, which he recounts rather than cites in the body of the text. The most effective example in the book is African. When a giraffe browses an umbrella acacia, the tree emits ethylene. The neighbouring acacias pick up the gas and immediately load their leaves with tannins, in quantities sufficient to make a large herbivore sick, or even kill it. And the giraffes know it: they browse facing into the wind, or else, when the air is still, they move about a hundred metres away before attacking the next tree, further than ethylene travels in motionless air. Three species reading one another.
The same logic in our latitudes. Elms and pines attacked by defoliating caterpillars identify the insect’s saliva, then emit pheromones that attract parasitoid wasps, which lay their eggs in the caterpillars, and the larvae devour them from the inside. Wohlleben also draws on a study from the University of Leipzig and the German Centre for Integrative Biodiversity Research: the tree tells the difference between a branch bitten by a roe deer, to which it responds by making its leaves taste bad, and a branch broken by a human hand, to which it responds simply by healing over. The plant does not react to the wound, it reacts to whoever inflicts it.
Then comes the famous network. The rootlets fuse with microscopic fungal filaments, the fungi take nearly 30% of the sugar produced by photosynthesis as they go, and in exchange they prospect the soil for nitrogen, phosphorus and minerals. Here Wohlleben refers to Simard’s work. He also describes the internal circulation: electrical signals moving at about one centimetre per minute, Edward Farmer’s research in Lausanne on a signalling system based on voltage variations whose form suggests an animal nervous system, and Monica Gagliano’s work in Western Australia on root crackling at 220 hertz, which the book presents as inaudible to our ears.
The chapter that rings truest is the one on school. Under the cover of an old beech wood, only 3% of the light remains. Wohlleben sees the young beeches as pupils. The one that twists to reach a gap is the dunce, it will die. The one that grows two long lateral branches is making a desperate calculation that will unbalance it. Constraint teaches slowness, and slowness makes the trees that last.
The thesis, and the wager on language
Five ideas carry the whole. The forest is a superorganism and not a collection of individuals, dense trees living longer and healthier lives than artificially spaced ones. Trees communicate, through three channels, chemical in the air, chemical and nutritive in the soil, electrical in the tissues. Industrial forestry makes them ill because it cuts them off from that network, and this is where description tips over into advocacy. Old trees are ecological capital far more than standing timber. Finally, and this is the delicate point, a human language is needed to say all this.
This last idea is not a slip of the pen, it is a declared strategy. He explained it to the New York Times: “I use a very human language. Scientific language removes all the emotion, and people don’t understand it anymore. When I say, ‘Trees suckle their children,’ everyone knows immediately what I mean.” Hence the friendships, the school, the social security, the burnout. Each chapter starts from a scene in the forest, passes through a physiological explanation, and ends on a flourish. No figures, no tables, no visible notes in the text, the references being relegated to the end of the volume. It has the rhythm of a guided tour, which is hardly surprising since the book grew out of the tours he used to give, and since it was his wife Miriam who pushed him to write.
This stance earned him a fight. A German petition, entitled “Auch im Wald: Fakten statt Märchen, Wissenschaft statt Wohlleben”, gathered 4,516 signatures from twenty-four countries. The sources agree neither on who started it nor on when it was launched. The detail worth noting is that it was not addressed to Wohlleben but to German newspapers and broadcasters, which it charged with a lack of critical thinking. Wohlleben, for his part, sums up his opponents this way: “They don’t dispute my facts because I quote all my scientific sources. They say I’m ‘esoteric’, which is a very bad word in their culture.”
One objection is nevertheless worth knowing, because it teaches something precise. In February 2023, Justine Karst, Melanie Jones and Jason Hoeksema published in Nature Ecology & Evolution a close review of the common mycorrhizal network. Their third conclusion is clear: the idea that mature trees preferentially send resources and defence signals to their own offspring rests on no published, peer-reviewed evidence. The network exists, resource transfer is still debated, maternal preference is not established. It is no small thing to know that before quoting the book in public.
What I keep, for my part, is the green stump. An organism that produces nothing any more and that its neighbours feed all the same, that is a field fact that will not fit in the box marked reflex. And I owe this book something very concrete: without it, the halls where I let people hear the plants would be three times emptier. It opened the door, readers came in that way, they arrive with the idea that the forest is speaking to someone. What remains is to give them something other than a metaphor to listen to.
Read in April 2017. Note written in 2026.
