Summary: The Hidden Life of Trees

The GIST

The Hidden Life of Trees: What They Feel, How They Communicate by Peter Wohlleben is the book that taught millions of readers to look at a forest as a society and not as scenery. First published in German in 2015 and in Jane Billinghurst's English translation in 2016, it sold more than 800,000 copies in Germany, reached bestseller lists in many other countries, and was later turned into a documentary film and a graphic novel. Its author is not a laboratory scientist. Wohlleben is a German forester, born in 1964, who spent more than twenty years with the state forestry commission, grew disillusioned with industrial forestry, and went on to manage an old beech wood for the village of Hümmel in the Eifel hills. The book began when his wife asked him to write down the things he tells visitors on his guided walks. He finished it in six months.

Its claim is simple and startling. A natural forest is not a crowd of individuals competing for light. It is a cooperative community, close to a single superorganism, in which trees sense, communicate, remember, share food and look after their kin. Wohlleben tells this in thirty-six short chapters and in deliberately human language: friendships, mothers, school, street kids. That choice made the book beloved, and it also made it controversial. If he is right, though, the way we manage forests, as fields of timber, has to change.

The Big Ideas

A forest is a community

The book opens with a discovery in Wohlleben's own woods. Walking among old beeches, he noticed what looked like mossy stones. They were the remains of an enormous beech stump, and when he scraped the surface with his penknife he found green underneath. The stump was alive. The tree had been felled four or five hundred years earlier. With no leaves it could not make food for itself, so there was only one explanation: the neighboring beeches had been feeding it through their roots for centuries.

From that stump he builds the idea of tree friendships. Trees pass nutrients to one another in two ways, either through the fungal threads that link their roots or by growing their roots directly together. He compares the result to an ant colony, a superorganism whose members survive by acting as one. And trees are not indiscriminate: he cites the researcher Massimo Maffei for the finding that they can tell their own roots from those of other species, and even from those of their relatives.

Why would a tree feed a rival? The chapter called "Social Security" gives the answer. Neighboring trees of the same species even out their differences, the strong subsidizing the weak. The forest is stronger as a group, so its weak members are supported and not abandoned.

The language of trees

Trees, Wohlleben insists, talk, and their first language is scent. His most famous example comes from the African savannah, where decades ago scientists watched giraffes feeding on umbrella thorn acacias. The trees did not like it. They released a warning gas, ethylene, that drifted to neighboring acacias, and the forewarned trees pumped toxins into their leaves before a single giraffe had touched them. The giraffes have learned the game. They walk on about a hundred yards, farther than the gas travels in still air, or they browse into the wind so the warning cannot run ahead of them.

Trees can taste as well. When caterpillars attack elms and pines, the trees identify the insect from its saliva and release scents that summon parasitic wasps. A tree cannot run, so it calls for help.

The slower and deeper channel is underground. Fungal networks woven through tree roots carry distress signals, water and nutrients across the forest, a system that has been nicknamed the wood wide web. It is the most celebrated idea in the book and, as we will see, the most disputed.

Mother trees and the virtue of growing slowly

The chapters on reproduction and childhood are where Wohlleben's human vocabulary is boldest. Trees of a species synchronize their seed production in mast years, flooding the forest with more seed than the animals can eat, and even so the odds are brutal: of all the seeds a tree makes in its long life, only a tiny fraction ever becomes an adult.

Those that do sprout grow up in deep shade under their parents, and this is the heart of his argument. A young beech beneath the canopy gets very little light and so grows very slowly. Wohlleben describes small beeches that have already been waiting eighty years beneath mother trees some two hundred years old, which he calls the equivalent of forty-year-olds in human terms. The waiting is not a misfortune. Slow growth lays down dense, tough wood, and dense wood resists fungi and storms and makes for a long life. Meanwhile the mothers, he says, "suckle their young," feeding them through the root network. He defends the phrase mother tree as an old technical term that foresters have used for a century.

This is also his sharpest criticism of his own profession. Conventional forestry thins a stand to give each tree more light, on the theory that trees compete. In his view thinning breaks up families, and the young trees that shoot upward in the sudden light grow fast, soft and short-lived.

In "Tree School" he goes further and argues that trees learn. A tree that has suffered through a drought changes how it uses water afterward, which implies a kind of memory.

How a forest builds its own world

The middle of the book widens from single trees to the forest as a working system. One run of chapters describes what a well-formed tree looks like, with a straight trunk, branches that begin high up and an even crown, and explains why: when wind pulls at the crown, the force runs all the way down to the roots, and a forked trunk is a point of weakness.

Then comes the argument that forests are their own climate control. Deciduous trees build a deep, leafy humus that holds moisture, and their branches slow the wind and still the air beneath them. Evaporation falls, the soil stays damp, and more trees can thrive, which strengthens the effect. An old, undisturbed forest does this far better than a managed plantation. A companion chapter presents the forest as a water pump that carries moisture far inland.

A tree is also a habitat. Wohlleben cites a study that found more than 2,000 insects from 241 species living on one old-growth tree, and he calls such trees the mother ships of biodiversity. Death does not end their usefulness. A fallen trunk is taken apart by a succession of fungi, bacteria and insects in what he calls a culinary relay race, until it has become soil. He rejects the forester's habit of clearing dead wood to protect the living: the organisms that consume dead trees are specialists and are no threat to healthy ones, so tidying the forest only starves it.

Stress, street kids and trees on the move

Trees have troubles, and Wohlleben describes them with sympathy. A tree has a limited budget of energy, and one that spends too much on growth has too little left for defense. When a gap opens in the canopy, many trees cannot resist a growth spurt, and they pay for it with greater vulnerability to fungi and insects. Other chapters describe how trees prepare for winter, how they track day length and warmth to know the season, and how individuals of the same species differ in what he does not hesitate to call character.

The saddest portrait is of city trees, his street kids. They grow up without family, with their roots hemmed in by pavement and their crowns cut back, lonely and under constant stress.

Forests as a whole, meanwhile, are slowly traveling. Trees migrate through their seeds, and there is a trade-off: light, winged seeds can ride a breeze for as much as a mile, while heavy acorns and chestnuts must rely on an alliance with animals to be carried anywhere. These chapters lead into his discussion of a changing climate and of non-native species.

More than a commodity

The closing chapters turn to people, including the question of whether forest air does us measurable good, and then to an ethical plea. For centuries we sorted life into humans, animals and plants, and treated plants as raw material without feeling. "Now it turns out that plants are, in many ways, very near to animals," Wohlleben says. He is not asking anyone to stop using wood. He is asking for a better balance, in the way that campaigners once asked for the humane treatment of farm animals: leave forests as undisturbed as possible, protect old growth, and abandon monocultures and heavy machinery. In his own woods he has set aside protected areas and replaced harvesters with woodworkers and horses. His key observation is that old trees in managed forests tend to die, while old trees in unmanaged forests go on living.

Readers should know that the book has been seriously challenged. Forestry scientists, especially in Germany, criticized its use of research to advance an ethical and almost spiritual program; a petition calling it unscientific drew 4,500 signatures, and one science writer accused him of cherry-picking data. The wood wide web in particular is an open argument: many researchers now question how much the fungal networks actually do, while others maintain the core findings are established science. Wohlleben's reply is that human words are how you make people care, and he declines the caricature: "They call me a 'tree-hugger', but I don't believe trees respond to hugs."

Putting It to Work

• Walk in the woods with new eyes. Look for stumps that are still alive, for young trees waiting in the shade, for fallen trunks turning into soil.
• Value old forests. They cool the air, hold water and shelter thousands of species in ways that young plantations cannot.
• Leave the dead wood. In a forest or a large garden, a rotting log is a home and a larder, not a mess.
• Plant what belongs. Favor native species suited to local conditions, and avoid monocultures.
• Be patient with growth. Slow-grown trees are stronger and longer-lived, a principle with obvious echoes beyond forestry.
• Have some sympathy for street trees. They are living under stress, so give their roots room and go easy on the pruning.
• Hold the metaphors lightly. Enjoy the wonder, and remember that parts of the science are still being argued over.

Who Should Read It

Nature lovers, hikers, gardeners and anyone who cares about forests and the climate will find this a quick and delightful read, written in plain language and in bite-sized chapters that can be taken in any order. The publisher promises that a walk in the woods will never be the same again, and many readers report exactly that. Those who want rigorous, heavily footnoted botany, or who are irritated by talk of tree kindergartens, may find it too loose and too sentimental. Read as one experienced forester's passionate account of what he has seen, it is hard to resist.

This has been a summary of The Hidden Life of Trees by Peter Wohlleben, giving you the GIST so you can decide if you want the REST.