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The Secret Life of Trees: The Astonishing Science of What Trees Feel and How They Communicate

“A tree can be only as strong as the forest that surrounds it.”

The Secret Life of Trees: The Astonishing Science of What Trees Feel and How They Communicate

Trees dominate the world’s the oldest living organisms. Since the dawn of our species, they have been our silent companions, permeating our most enduring tales and never ceasing to inspire fantastical cosmogonies. Hermann Hesse called them “the most penetrating of preachers.” A forgotten seventeenth-century English gardener wrote of how they “speak to the mind, and tell us many things, and teach us many good lessons.”

But trees might be among our lushest metaphors and sensemaking frameworks for knowledge precisely because the richness of what they say is more than metaphorical — they speak a sophisticated silent language, communicating complex information via smell, taste, and electrical impulses. This fascinating secret world of signals is what German forester Peter Wohlleben explores in The Hidden Life of Trees: What They Feel, How They Communicate (public library).

Wohlleben chronicles what his own experience of managing a forest in the Eifel mountains in Germany has taught him about the astonishing language of trees and how trailblazing arboreal research from scientists around the world reveals “the role forests play in making our world the kind of place where we want to live.” As we’re only just beginning to understand nonhuman consciousnesses, what emerges from Wohlleben’s revelatory reframing of our oldest companions is an invitation to see anew what we have spent eons taking for granted and, in this act of seeing, to care more deeply about these remarkable beings that make life on this planet we call home not only infinitely more pleasurable, but possible at all.

Illustration by Arthur Rackham for a rare 1917 edition of the Brothers Grimm fairy tales. (Available as a print.)

But Wohlleben’s own career began at the opposite end of the caring spectrum. As a forester tasked with optimizing the forest’s output for the lumber industry, he self-admittedly “knew about as much about the hidden life of trees as a butcher knows about the emotional life of animals.” He experienced the consequence of what happens whenever we turn something alive, be it a creature or a work of art, into a commodity — the commercial focus of his job warped how he looked at trees.

Then, about twenty years ago, everything changed when he began organizing survival training and log-cabin tours for tourists in his forest. As they marveled at the majestic trees, the enchanted curiosity of their gaze reawakened his own and his childhood love of nature was rekindled. Around the same time, scientists began conducting research in his forest. Soon, every day became colored with wonderment and the thrill of discovery — no longer able to see trees as a currency, he instead saw them as the priceless living wonders that they are. He recounts:

Life as a forester became exciting once again. Every day in the forest was a day of discovery. This led me to unusual ways of managing the forest. When you know that trees experience pain and have memories and that tree parents live together with their children, then you can no longer just chop them down and disrupt their lives with large machines.

The revelation came to him in flashes, the most eye-opening of which happened on one of his regular walks through a reserve of old beech tree in his forest. Passing by a patch of odd mossy stones he had seen many times before, he was suddenly seized with a new awareness of their strangeness. When he bent down to examine them, he made an astonishing discovery:

The stones were an unusual shape: they were gently curved with hollowed-out areas. Carefully, I lifted the moss on one of the stones. What I found underneath was tree bark. So, these were not stones, after all, but old wood. I was surprised at how hard the “stone” was, because it usually takes only a few years for beechwood lying on damp ground to decompose. But what surprised me most was that I couldn’t lift the wood. It was obviously attached to the ground in some way. I took out my pocketknife and carefully scraped away some of the bark until I got down to a greenish layer. Green? This color is found only in chlorophyll, which makes new leaves green; reserves of chlorophyll are also stored in the trunks of living trees. That could mean only one thing: this piece of wood was still alive! I suddenly noticed that the remaining “stones” formed a distinct pattern: they were arranged in a circle with a diameter of about 5 feet. What I had stumbled upon were the gnarled remains of an enormous ancient tree stump. All that was left were vestiges of the outermost edge. The interior had completely rotted into humus long ago — a clear indication that the tree must have been felled at least four or five hundred years earlier.

How can a tree cut down centuries ago could still be alive? Without leaves, a tree is unable to perform photosynthesis, which is how it converts sunlight into sugar for sustenance. The ancient tree was clearly receiving nutrients in some other way — for hundreds of years.

Beneath the mystery lay a fascinating frontier of scientific research, which would eventually reveal that this tree was not unique in its assisted living. Neighboring trees, scientists found, help each other through their root systems — either directly, by intertwining their roots, or indirectly, by growing fungal networks around the roots that serve as a sort of extended nervous system connecting separate trees. If this weren’t remarkable enough, these arboreal mutualities are even more complex — trees appear able to distinguish their own roots from those of other species and even of their own relatives.

Art by Judith Clay from Thea’s Tree

Wohlleben ponders this astonishing sociality of trees, abounding with wisdom about what makes strong human communities and societies:

Why are trees such social beings? Why do they share food with their own species and sometimes even go so far as to nourish their competitors? The reasons are the same as for human communities: there are advantages to working together. A tree is not a forest. On its own, a tree cannot establish a consistent local climate. It is at the mercy of wind and weather. But together, many trees create an ecosystem that moderates extremes of heat and cold, stores a great deal of water, and generates a great deal of humidity. And in this protected environment, trees can live to be very old. To get to this point, the community must remain intact no matter what. If every tree were looking out only for itself, then quite a few of them would never reach old age. Regular fatalities would result in many large gaps in the tree canopy, which would make it easier for storms to get inside the forest and uproot more trees. The heat of summer would reach the forest floor and dry it out. Every tree would suffer.

Every tree, therefore, is valuable to the community and worth keeping around for as long as possible. And that is why even sick individuals are supported and nourished until they recover. Next time, perhaps it will be the other way round, and the supporting tree might be the one in need of assistance.

[…]

A tree can be only as strong as the forest that surrounds it.

One can’t help but wonder whether trees are so much better equipped at this mutual care than we are because of the different time-scales on which our respective existences play out. Is some of our inability to see this bigger picture of shared sustenance in human communities a function of our biological short-sightedness? Are organisms who live on different time scales better able to act in accordance with this grander scheme of things in a universe that is deeply interconnected?

To be sure, even trees are discriminating in their kinship, which they extend in varying degrees. Wohlleben explains:

Every tree is a member of this community, but there are different levels of membership. For example, most stumps rot away into humus and disappear within a couple of hundred years (which is not very long for a tree). Only a few individuals are kept alive over the centuries… What’s the difference? Do tree societies have second-class citizens just like human societies? It seems they do, though the idea of “class” doesn’t quite fit. It is rather the degree of connection — or maybe even affection — that decides how helpful a tree’s colleagues will be.

These relationships, Wohlleben points out, are encoded in the forest canopy and visible to anyone who simply looks up:

The average tree grows its branches out until it encounters the branch tips of a neighboring tree of the same height. It doesn’t grow any wider because the air and better light in this space are already taken. However, it heavily reinforces the branches it has extended, so you get the impression that there’s quite a shoving match going on up there. But a pair of true friends is careful right from the outset not to grow overly thick branches in each other’s direction. The trees don’t want to take anything away from each other, and so they develop sturdy branches only at the outer edges of their crowns, that is to say, only in the direction of “non-friends.” Such partners are often so tightly connected at the roots that sometimes they even die together.

Art by Cécile Gambini from Strange Trees by Bernadette Pourquié

But trees don’t interact with one another in isolation from the rest of the ecosystem. The substance of their communication, in fact, is often about and even to other species. Wohlleben describes their particularly remarkable olfactory warning system:

Four decades ago, scientists noticed something on the African savannah. The giraffes there were feeding on umbrella thorn acacias, and the trees didn’t like this one bit. It took the acacias mere minutes to start pumping toxic substances into their leaves to rid themselves of the large herbivores. The giraffes got the message and moved on to other trees in the vicinity. But did they move on to trees close by? No, for the time being, they walked right by a few trees and resumed their meal only when they had moved about 100 yards away.

The reason for this behavior is astonishing. The acacia trees that were being eaten gave off a warning gas (specifically, ethylene) that signaled to neighboring trees of the same species that a crisis was at hand. Right away, all the forewarned trees also pumped toxins into their leaves to prepare themselves. The giraffes were wise to this game and therefore moved farther away to a part of the savannah where they could find trees that were oblivious to what was going on. Or else they moved upwind. For the scent messages are carried to nearby trees on the breeze, and if the animals walked upwind, they could find acacias close by that had no idea the giraffes were there.

Because trees operate on time scales dramatically more extended than our own, they operate far more slowly than we do — their electrical impulses crawl at the speed of a third of an inch per minute. Wohlleben writes:

Beeches, spruce, and oaks all register pain as soon as some creature starts nibbling on them. When a caterpillar takes a hearty bite out of a leaf, the tissue around the site of the damage changes. In addition, the leaf tissue sends out electrical signals, just as human tissue does when it is hurt. However, the signal is not transmitted in milliseconds, as human signals are; instead, the plant signal travels at the slow speed of a third of an inch per minute. Accordingly, it takes an hour or so before defensive compounds reach the leaves to spoil the pest’s meal. Trees live their lives in the really slow lane, even when they are in danger. But this slow tempo doesn’t mean that a tree is not on top of what is happening in different parts of its structure. If the roots find themselves in trouble, this information is broadcast throughout the tree, which can trigger the leaves to release scent compounds. And not just any old scent compounds, but compounds that are specifically formulated for the task at hand.

The upside of this incapacity for speed is that there is no need for blanket alarmism — the recompense of trees’ inherent slowness is an extreme precision of signal. In addition to smell, they also use taste — each species produces a different kind of “saliva,” which can be infused with different pheromones targeted at warding off a specific predator.

Wohlleben illustrates the centrality of trees in Earth’s ecosystem with a story about Yellowstone National Park that demonstrates “how our appreciation for trees affects the way we interact with the world around us”:

It all starts with the wolves. Wolves disappeared from Yellowstone, the world’s first national park, in the 1920s. When they left, the entire ecosystem changed. Elk herds in the park increased their numbers and began to make quite a meal of the aspens, willows, and cottonwoods that lined the streams. Vegetation declined and animals that depended on the trees left. The wolves were absent for seventy years. When they returned, the elks’ languorous browsing days were over. As the wolf packs kept the herds on the move, browsing diminished, and the trees sprang back. The roots of cottonwoods and willows once again stabilized stream banks and slowed the flow of water. This, in turn, created space for animals such as beavers to return. These industrious builders could now find the materials they needed to construct their lodges and raise their families. The animals that depended on the riparian meadows came back, as well. The wolves turned out to be better stewards of the land than people, creating conditions that allowed the trees to grow and exert their influence on the landscape.

Art by William Grill from The Wolves of Currumpaw

This interconnectedness isn’t limited to regional ecosystems. Wohlleben cites the work of Japanese marine chemist Katsuhiko Matsunaga, who discovered that trees falling into a river can change the acidity of the water and thus stimulate the growth of plankton — the elemental and most significant building block of the entire food chain, on which our own sustenance depends.

In the remainder of The Hidden Life of Trees, Wohlleben goes on to explore such fascinating aspects of arboreal communication as how trees pass wisdom down to the next generation through their seeds, what makes them live so long, and how forests handle immigrants. Complement it with this wonderful illustrated atlas of the world’s strangest trees and an 800-year visual history of trees as symbolic diagrams.

BP

Wander: Natascha McElhone Reads Hermann Hesse’s 100-Year-Old Love Letter to Trees in a Virtual Mental Health Walk Through Kew Gardens

“In their highest boughs the world rustles, their roots rest in infinity; but they do not lose themselves there, they struggle with all the force of their lives for one thing only: to fulfill themselves according to their own laws… to represent themselves. Nothing is holier, nothing is more exemplary than a beautiful, strong tree.”

Wander: Natascha McElhone Reads Hermann Hesse’s 100-Year-Old Love Letter to Trees in a Virtual Mental Health Walk Through Kew Gardens

In the final years of his life, the great neurologist Oliver Sacks reflected on the physiological and psychological healing power of nature, observing that in forty years of medical practice, he had found only two types of non-pharmaceutical therapy helpful to his patients: music and gardens. It was in a garden, too, that Virginia Woolf, bedeviled by lifelong mental illness, found the consciousness-electrifying epiphany that enabled her to make some of humanity’s most transcendent art despite her private suffering.

When my dear friend Natascha McElhone (who narrated Figuring) was asked to choose a piece of literature with which to narrate a tour of the Royal Botanic Gardens, Kew, for an episode of Wander — a lovely series by filmmaker Beau Kerouac, benefiting Britain’s Mental Health Foundation and helping quarantined people virtually visit some of the world’s most beloved parks and cultural institutions, accompanied by some of the world’s most beloved literary and artistic voices — Natascha chose a wondrous 100-year-old love letter to trees by Hermann Hesse (July 2, 1877–August 9, 1962), which she had saved from Brain Pickings nearly a decade ago. Originally published in Hesse’s 1920 collection of fragments, Wandering: Notes and Sketches (public library), it comes newly alive in this transportive, transcendent journey through the screen and past it, into a lush wonderland of nature’s aliveness, with two uncommonly beautiful voices as the sherpas.

For me, trees have always been the most penetrating preachers. I revere them when they live in tribes and families, in forests and groves. And even more I revere them when they stand alone. They are like lonely persons. Not like hermits who have stolen away out of some weakness, but like great, solitary men, like Beethoven and Nietzsche. In their highest boughs the world rustles, their roots rest in infinity; but they do not lose themselves there, they struggle with all the force of their lives for one thing only: to fulfill themselves according to their own laws, to build up their own form, to represent themselves. Nothing is holier, nothing is more exemplary than a beautiful, strong tree. When a tree is cut down and reveals its naked death-wound to the sun, one can read its whole history in the luminous, inscribed disk of its trunk: in the rings of its years, its scars, all the struggle, all the suffering, all the sickness, all the happiness and prosperity stand truly written, the narrow years and the luxurious years, the attacks withstood, the storms endured. And every young farmboy knows that the hardest and noblest wood has the narrowest rings, that high on the mountains and in continuing danger the most indestructible, the strongest, the ideal trees grow.

Trees are sanctuaries. Whoever knows how to speak to them, whoever knows how to listen to them, can learn the truth. They do not preach learning and precepts, they preach, undeterred by particulars, the ancient law of life.

A tree says: A kernel is hidden in me, a spark, a thought, I am life from eternal life. The attempt and the risk that the eternal mother took with me is unique, unique the form and veins of my skin, unique the smallest play of leaves in my branches and the smallest scar on my bark. I was made to form and reveal the eternal in my smallest special detail.

A tree says: My strength is trust. I know nothing about my fathers, I know nothing about the thousand children that every year spring out of me. I live out the secret of my seed to the very end, and I care for nothing else. I trust that God is in me. I trust that my labor is holy. Out of this trust I live.

When we are stricken and cannot bear our lives any longer, then a tree has something to say to us: Be still! Be still! Look at me! Life is not easy, life is not difficult. Those are childish thoughts… Home is neither here nor there. Home is within you, or home is nowhere at all.

A longing to wander tears my heart when I hear trees rustling in the wind at evening. If one listens to them silently for a long time, this longing reveals its kernel, its meaning. It is not so much a matter of escaping from one’s suffering, though it may seem to be so. It is a longing for home, for a memory of the mother, for new metaphors for life. It leads home. Every path leads homeward, every step is birth, every step is death, every grave is mother.

So the tree rustles in the evening, when we stand uneasy before our own childish thoughts: Trees have long thoughts, long-breathing and restful, just as they have longer lives than ours. They are wiser than we are, as long as we do not listen to them. But when we have learned how to listen to trees, then the brevity and the quickness and the childlike hastiness of our thoughts achieve an incomparable joy. Whoever has learned how to listen to trees no longer wants to be a tree. He wants to be nothing except what he is. That is home. That is happiness.

“Perspective” by Maria Popova

For a lyrical kindred-spirited counterpart, visit one of Earth’s greatest forests with Pablo Neruda and astronaut Leland Melvin, then savor Amanda Palmer’s reading of Mary Oliver’s spare and splendid poem “When I Am Among the Trees” and this cinematic love letter to the wilderness, inspired by the great naturalist John Muir, who saw the universe as “an infinite storm of beauty.”

BP

The Cosmic Miracle of Trees: Astronaut Leland Melvin Reads Pablo Neruda’s Love Letter to Earth’s Forests

“Anyone who hasn’t been in the Chilean forest doesn’t know this planet. I have come out of that landscape, that mud, that silence, to roam, to go singing through the world.”

The Cosmic Miracle of Trees: Astronaut Leland Melvin Reads Pablo Neruda’s Love Letter to Earth’s Forests

“Today, for some, a universe will vanish,” Jane Hirshfield writes in her stunning poem about the death of a tree a quarter millennium after William Blake observed in his most passionate letter that how we see a tree is how we see the world, and in the act of seeing we reveal what we are: “The tree which moves some to tears of joy is in the eyes of others only a green thing which stands in the way,” he wrote. “As a man is, so he sees.”

If a single tree is home to a miniature universe of life, and if we are learning with wide-eyed wonder that a tree is not a self-contained world but a synaptic node in a complex cosmos of relationships in constant and astonishing communication with other nodes, relationships that weave the fabric of earthly life, what does it make us — what does it reveal about our character, as a planetary people and a civilization — to watch the world’s forests vanish in flames before our eyes, in wildfires so ferocious as to be visible from space?

Art from Trees at Night by Art Young, 1926. (Available as a print.)

A century after Walt Whitman turned to trees as our wisest moral teachers and a generation before Wangari Maathai defended them with her life in a movement of moral courage that won her the Nobel Peace Prize, the Nobel-winning Chilean poet Pablo Neruda (July 12, 1904–September 23, 1973) — one of humanity’s furthest-seeing and lushest-minded artists — shone a gorgeous sidewise gleam at an answer by way of celebration rather than lamentation in a passage from his Memoirs (public library), posthumously published in English the year the Voyager spacecraft captured that poetry-fomenting first glimpse of our Pale Blue Dot seen from far away. (Translated from the Spanish by Hardie St. Martin, this treasure of a book is now — unfathomably, tragically, a civilizational embarrassment — out of print.)

At the 2020 Universe in Verse, celebrating fifty years of Earth Day, astronaut and poetry-lover Leland Melvin — one of a fraction of a fraction of a percentage of humans in the history of our species to have left this rare planet, to have seen its forests and its intricate living web of relationships from the cosmic perspective, and to have returned loving it all the more passionately — breathed new life into Neruda’s forgotten words with a soulful reading of that passage:

Under the volcanoes, beside the snow-capped mountains, among the huge lakes, the fragrant, the silent, the tangled Chilean forest… My feet sink down into the dead leaves, a fragile twig crackles, the giant rauli trees rise in all their bristling height, a bird from the cold jungle passes over, flaps its wings, and stops in the sunless branches. And then, from its hideaway, it sings like an oboe… The wild scent of the laurel, the dark scent of the boldo herb, enter my nostrils and flood my whole being… The cypress of the Guaitecas blocks my way… This is a vertical world: a nation of birds, a plenitude of leaves… I stumble over a rock, dig up the uncovered hollow, an enormous spider covered with red hair stares up at me, motionless, as huge as a crab… A golden carabus beetle blows its mephitic breath at me, as its brilliant rainbow disappears like lightning… Going on, I pass through a forest of ferns much taller than I am: from their cold green eyes sixty tears splash down on my face and, behind me, their fans go on quivering for a long time… A decaying tree trunk: what a treasure!… Black and blue mushrooms have given it ears, red parasite plants have covered it with rubies, other lazy plants have let it borrow their beards, and a snake springs out of the rotted body like a sudden breath, as if the spirit of the dead trunk were slipping away from it… Farther along, each tree stands away from its fellows… They soar up over the carpet of the secretive forest, and the foliage of each has its own style, linear, bristling, ramulose, lanceolate, as if cut by shears moving in infinite ways… A gorge; below, the crystal water slides over granite and jasper… A butterfly goes past, bright as a lemon, dancing between the water and the sunlight… Close by, innumerable calceolarias nod their little yellow heads in greeting… High up, red copihues (Lapageria rosea) dangle like drops from the magic forest’s arteries… A fox cuts through the silence like a flash, sending a shiver through the leaves, but silence is the law of the plant kingdom… The barely audible cry of some bewildered animal far off… The piercing interruption of a hidden bird… The vegetable world keeps up its low rustle until a storm chums up all the music of the earth.

Anyone who hasn’t been in the Chilean forest doesn’t know this planet.

I have come out of that landscape, that mud, that silence, to roam, to go singing through the world.

Art from Trees at Night by Art Young, 1926. (Available as a print.)

Complement with poet and painter Rebecca Hey’s lovely illustrations for the world’s first encyclopedia of trees, Mary Oliver’s radiant poem “When I Am Among the Trees” radiantly read by Amanda Palmer, the uncommonly wonderful picture-book The Forest, and the poetic nature writer Robert Macfarlane — who also read at the 2020 Universe in Verse — on how trees illuminate the secret of true love, then savor other highlights from this poetic celebration of the science and splendor of nature: a sublimely beautiful animation of Marie Howe’s stirring poem about our cosmic belonging and the meaning of home, inspired by Stephen Hawking; astrophysicist Janna Levin reading “Antidotes to Fear of Death” by the late, great astronomer and poet Rebecca Elson; Amanda Palmer reading “Einstein’s Mother” by former U.S. Poet Laureate and Universe in Verse alumna Tracy K. Smith; and artist Ohara Hale’s lyrical watercolor adaptation of Mojave American poet Natalie Diaz’s ode to brokenness as a portal to belonging and resilience.

BP

Relationship Lessons from Trees

“I think of good love as something that roots, not rots, over time, and of the hyphae that are weaving through the ground below me, reaching out through the soil in search of mergings.”

Relationship Lessons from Trees

“The tree which moves some to tears of joy is in the eyes of others only a green thing which stands in the way,” William Blake wrote in his most beautiful letter. “As a man is, so he sees.” Walt Whitman saw trees as the wisest of teachers; Hermann Hesse as our mightiest consolation for mortality. Wangari Maathai rooted in them a colossal act of resistance that earned her the Nobel Peace Prize. Poets have elegized their wisdom, artists have drawn from their form resonance with our human emotions, scientists are only just beginning to uncover their own secret language.

Robert Macfarlane — a rare enchanter who entwines the scientific and the poetic in his lyrical explorations of the natural world — offers a crowning curio in the canon of wisdom on human life drawn from trees in a passage from Underland: A Deep Time Journey (public library) — his magnificent soul-guided, science-lit tour of the hidden universe beneath our feet.

Art by Arthur Rackham for a rare 1917 edition of the Brothers Grimm fairy tales. (Available as a print.)

Macfarlane writes:

Lying there among the trees, despite a learned wariness towards anthropomorphism, I find it hard not to imagine these arboreal relations in terms of tenderness, generosity and even love: the respectful distance of their shy crowns, the kissing branches that have pleached with one another, the unseen connections forged by root and hyphae between seemingly distant trees. I remember something Louis de Bernières has written about a relationship that endured into old age: “we had roots that grew towards each other underground, and when all the pretty blossom had fallen from our branches we found that we were one tree and not two.” As someone lucky to live in a long love, I recognize that gradual growing-towards and subterranean intertwining; the things that do not need to be said between us, the unspoken communication which can sometimes tilt troublingly towards silence, and the sharing of both happiness and pain. I think of good love as something that roots, not rots, over time, and of the hyphae that are weaving through the ground below me, reaching out through the soil in search of mergings. Theirs, too, seems to me then a version of love’s work.

Art from Trees at Night by Art Young, 1926. (Available as a print.)

Beneath the canopy, Macfarlane marvels at the slim contour of empty space around each tree’s crown — a phenomenon known as crown shyness, “whereby individual forest trees respect each other’s space, leaving slender running gaps between the end of one tree’s outermost leaves and the start of another’s.”

In this, too, I see a poignant lesson in love, evocative of Rilke and what may be the greatest relationship advice ever committed to words: “I hold this to be the highest task of a bond between two people: that each should stand guard over the solitude of the other.”

“Broken/hearted” by Maria Popova. (Available as a print.)

Couple this tiny fragment of the sweepingly wondrous Underland with Amanda Palmer’s lovely reading of Mary Oliver’s poem “When I Am Among the Trees,” then revisit Kahlil Gibran on the difficult balance of intimacy and independence in love.

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