Talking trees

Print edition : February 03, 2017

Four decades ago, scientists noticed that umbrella thorn acacias on the African savannah pumped toxic substances into their leaves to stop giraffes from feeding on them. The trees also alerted other acacia trees in the vicinity about the threat. Here, a giraffe near acacia trees in Nairobi National Park, Kenya, in November 2016. Photo: Ben Curtis/AP

Beech trees in a forest in the Bieszczady mountains in Poland. Photo: Kacper Pempel /REUTERS

In describing how trees communicate and have a sense of community and feelings, the book brings soul back to science without making anyone feel sentimental or squeamish about the word and its associations.

SOME years ago an official of the venerable Forest Research Institute in Dehradun told this correspondent a story. The details are sadly blurred because of the years that have passed, and unfortunately when the institute was contacted again, no one could corroborate the story, but the gist of it is this. There were three large old trees on the campus in pre-Independence days. At some point some construction work began that resulted in one of them being hidden from the other two. The foresters noticed that this isolated tree started dying, and they did not know why. After eliminating all possibilities, the foresters, though initially loath to acknowledge it, came to the conclusion that the tree was pining for its companions. Whether or not it was revived is again lost to memory, but that does not take away from the poignancy of the story nor from the fact that men of science had accepted the fact that the tree was pining.

There is a beautiful rubaii by the poet Niraj:

Sukhan ko ahley sukhan samjhe zubaan ko ahley zubaan samjhe

Yeh ashkon ki ibaarat kaun iska tarjuna samjhe

Us se to aapne guldaste ki raunaq phursad hi kaha hai

Gulchieen ko ki vho daarde gulistan samjhe

A literal translation would take away from the depth of thought expressed, but the essence of the first two lines is this: fundamentally one’s experiences are one’s own, that understanding is limited to one’s own experiences. The last two lines of the rubaii go on to express this idea with poignancy. They say that a gardener’s only concern is the lustre of his bouquet, and as he wanders through the garden selecting flowers to enhance his bouquet, he is unaware of the wave of fear and pain that flows through the garden as the flowers feel his predatory presence. Perhaps Niraj said this figuratively, but plants are sentient beings, and Peter Wohlleben’s The Hidden Life of Trees illustrates this with clarity, gentleness, wit and, most importantly for those who would scoff, scientific rigour.

Career forester

Wohlleben is a career forester. He introduces himself in the preface: “When I began my professional career as a forester, I knew as much about the hidden life of trees as a butcher knows about the emotional life of animals.” He goes on to admit that forest management is essentially about extracting commerce from the forest, but his solitary wanderings in the woodlands proved to be great lessons.

The book brings into question the whole idea of forest management, that is, the role man has bestowed on himself as he plants, cuts, trims and “manages” forests for commercial gain. The reality is that forests manage themselves with far more efficiency than man ever could, and that is because trees, like any living organism, are guided by a survival instinct that tells them what is best for them. The author explains. A forester will cut down a tree when it is the right size for a sawmill. He presumes that the area opened up will give trees more space to grow, but this, says Wohlleben, is a wrong presumption.

“Trees are capable of friendship and go so far as to feed each other.” In fact, the turning point in Wohlleben’s life as a forester came when he noticed an old stump that he initially thought was a rock. The story is told at the start of the book in the chapter titled “Friendships”. Walking in the woodland he manages, he was drawn to some stones he had always seen but was suddenly more curious about. He lifted the moss covering them and found bark underneath. He scraped some away and found a greenish layer. That meant chlorophyll and that meant life. A while later he figured out the age of the rock-like stumps and was astonished to find out that they “must have been felled 400 or 500 years earlier”. The mystery lay in the continued survival of the stumps without leaves and photosynthesis. Wohlleben found the answer in a simple process. The stumps were “getting assistance from neighbouring trees, specifically from their roots”. Unable to bring himself to dig up the stumps, Wohlleben surmised that “the surrounding beeches were pumping sugar to the stump to keep it alive”. Friendship indeed.

Fascinating lines of reasoning

From this promising start, the book leapfrogs from one fascinating line of reasoning to another. Scent is part of tree communication, and Wohlleben illustrates this with an example. “[F]our 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 behaviour is astonishing. The acacia trees that were being eaten gave off a warning gas (specifically, ethylene) that signalled to neighbouring 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.”

Scent communication is just one of the wonders that Wohlleben opens our eyes to. Plants communicate or “talk”, as he plainly puts it, in many other ways too. “If trees are weakened, it could be that they lose their conversational skills along with their ability to defend themselves. Otherwise, it’s difficult to explain why insect pests specifically seek out trees whose health is already compromised. It’s conceivable that to do this, insects listen to trees’ urgent chemical warnings, and then test trees that don’t pass the message on by taking a bite of their leaves or bark. A tree’s silence could be because of a serious illness or, perhaps, the loss of its fungal network, which would leave the tree completely cut off from the latest news. The tree no longer registers approaching disaster, and the doors are open for the caterpillar and beetle buffet.”

Wohlleben speculates about selective breeding among plants and believes that “cultivated plants have, for the most part, lost their ability to communicate above or below ground… and therefore they are easy prey for insect pests. That is one reason modern agriculture uses so many pesticides.” His advice: “Perhaps farmers can learn from the forests and breed a little more wilderness back into their grain and potatoes so that they’ll be more talkative in the future.”

The book is essentially a coming together of the author’s own experiences and knowledge and the discoveries others have made over the decades about plant life. For instance, the term “wood wide web” to describe the underground communication of plants was coined by the journal Nature for the discovery of warning signals being sent through fungal networks around root tips. Suzanne Simard of the University of British Columbia, Vancouver, did the research for this.

Then there is the work done by Monica Gagliano from the University of Western Australia, along with colleagues from Bristol and Florence, who “has, quite literally, had her ear to the ground”. Monica Gagliano’s work showed that roots crackle at a frequency of 220 hertz, causing other roots to orient their tips in the direction of the sound; they were literally listening in. Or the remarkable findings on photosynthesis by students from the Institute for Environmental Research at RWTH Aachen, Germany. Quoting from unpublished research from RWTH, Wohlleben says that the students discovered that within a forest each beech tree grows in a unique location even if one tree is just yards away from another tree. The nutrition, water retention capacity, access to light, and so on, vary, which might lead one to think that the trees would all photosynthesise at varying rates, but the students found that the rate of photosynthesis was the same.

“The trees, it seems, are equalising differences between the strong and the weak…. This equalisation is taking place underground, through the roots. There’s obviously a lively exchange going on down there. Whoever has an abundance of sugar hands some over; whoever is running short gets help…. It’s a bit like the way social security systems operate to ensure individual members of society don’t fall too far behind.”

While Wohlleben’s own life has evolved from working for the forestry commission in Germany to running his own environment-friendly woodland where he aims for the return of primeval forests, he still straddles two worlds to some extent. He relates an anecdote on how beeches were introduced to an area where only pines grew.

It must be understood that there is no old world forest in Europe any more. They are all plantations to that extent. The beeches planted in this particular corner of Germany were meant to neutralise the acid in the fallen pine needles “to make them more palatable to the creatures in the soil”. The role of the beeches was to be one of service trees, never to be cut for lumber. But after some decades, the beeches “showed what they were made of”. Their annual leaf fall changed the atmospherics of the forest, making it more humid, and the thriving beech trees prevented the wind from cutting through the forest, thereby further conserving the humidity.

Soon the area became more suitable for deciduous trees than for the “frugal conifer”. Whether this management of the forest is good or bad cannot be judged because old growth forests in Europe were cut down long ago, and as Wohlleben says: “[P]eople put the forests in places that made sense to them.” He does, however, say that “the struggles and strategies in forests left to their own devices, and the tension created when forests are planted instead of evolving at their own pace are issues that resonate far beyond my experiences”.


The beauty of Wohlleben’s book is, of course, in what he writes, but even more than that is the fact that it has become a bestseller. The book was written and published in German, and thanks must be given to Wohlleben’s translator, who has made the book not just readable but unputdownable with its matter-of-fact tone, gentle humour and non-patronising writing. Much of what the author says is known and even more is believed without supporting “fact”, but when all this information comes from a formally trained scientist, even those who jump at dismissing such knowledge are willing to listen to some one say (if not accept) that trees could have a system of communication, a sense of community and also feelings.

Wohlleben’s thinking is fresh, youthful, experienced, excited, full of wonder and yet faithful to his basic training of science. This is what gives The Hidden Life of Trees such mass appeal. The book brings soul back to science without making anyone feel sentimental or squeamish about the word and its associations. It is the breaking of this barrier that adds considerably to the book’s appeal.