The Hidden Life of Trees: What They Feel, How They Communicate — Discoveries from a Secret World

by Peter Wohlleben

The reason trees share food and communicate is that they need each other. It takes a forest to create a microclimate suitable for tree growth and sustenance. So it’s not surprising that isolated trees have far shorter lives than those living connected together in forests.

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.

It appears that nutrient exchange and helping neighbors in times of need is the rule, and this leads to the conclusion that forests are superorganisms with interconnections much like ant colonies.

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.

In the symbiotic community of the forest, not only trees but also shrubs and grasses—and possibly all plant species—exchange information this way. However, when we step into farm fields, the vegetation becomes very quiet. Thanks to selective breeding, our cultivated plants have, for the most part, lost their ability to communicate above or below ground—you could say they are deaf and dumb—and therefore they are easy prey for insect pests.12 That is one reason why modern agriculture uses so many pesticides. Perhaps farmers can learn from the forests and breed a little more wildness back into their grain and potatoes so that they’ll be more talkative in the future.

Their well-being depends on their community, and when the supposedly feeble trees disappear, the others lose as well. When that happens, the forest is no longer a single closed unit. Hot sun and swirling winds can now penetrate to the forest floor and disrupt the moist, cool climate.

“A chain is only as strong as its weakest link.” Trees could have come up with this old craftsperson’s saying. And because they know this intuitively, they do not hesitate to help each other out.

Statistically speaking, each tree raises exactly one adult offspring to take its place. For those that don’t make it, seeds may germinate and young seedlings may vegetate for a few years, or even for a few decades, in the shadows, but sooner or later, they run out of steam. They are not alone. Dozens of offspring from other years also stand at their mothers’ feet, and by and by, most give up and return to humus. Eventually, a few of the lucky ones that have been carried to open spaces on the forest floor by the wind or by animals get a good start in life and grow to adulthood.

When I examined one of my young beech trees, it turned out that a single 8-inch-long twig already had twenty-five of these swellings. I could find no other indicator of the tree’s age on its tiny trunk, which was no more than a third of an inch in diameter, but when I carefully extrapolated the age of the tree from the age of the branch, I discovered that the tree must have been at least eighty years old, maybe more. That seemed unbelievable at the time, until I continued my investigations into ancient forests. Now I know: it is absolutely normal.

The method used in this upbringing is light deprivation. But what purpose does this restriction serve? Don’t parents want their offspring to become independent as quickly as possible? Trees, at least, would answer this question with a resounding no, and recent science backs them up. Scientists have determined that slow growth when the tree is young is a prerequisite if a tree is to live to a ripe old age.

If trees are capable of learning (and you can see they are just by observing them), then the question becomes: Where do they store what they have learned and how do they access this information? After all, they don’t have brains to function as databases and manage processes. It’s the same for all plants, and that’s why some scientists are skeptical and why many of them banish to the realm of fantasy the idea of plants’ ability to learn. But, once again, along comes the Australian scientist Dr. Monica Gagliano.

With the help of mycelium of an appropriate species for each tree—for instance, the oak milkcap and the oak—a tree can greatly increase its functional root surface so that it can suck up considerably more water and nutrients.

things become dire for the fungi and their trees despite all this support, then the fungi can take radical action, as in the case of the pine and its partner Laccaria bicolor, or the bicolored deceiver. When there is a lack of nitrogen, the latter releases a deadly toxin into the soil, which causes minute organisms such as springtails to die and release the nitrogen tied up in their bodies, forcing them to become fertilizer for both the trees and the fungi.

They registered a soft murmur in the trees. Above all, at night. At this time of day, most of the water is stored in the trunk, as the crown takes a break from photosynthesis and hardly transpires at all. The trees pump themselves so full of water their trunks sometimes increase in diameter. The water is held almost completely immobile in the inner transportation tubes. Nothing flows. So where are the noises coming from? The researchers think they are coming from tiny bubbles of carbon dioxide in the narrow water-filled tubes.30 Bubbles in the pipes? That means the supposedly continuous column of water is interrupted thousands of times. And if that is the case, transpiration, cohesion, and capillary action contribute very little to water transport. So many questions remain unanswered. Perhaps we are poorer for having lost a possible explanation or richer for having gained a mystery. But aren’t both possibilities equally intriguing?

Some species of weevil, mostly those that live on the forest floor, can no longer fly because they have become accustomed to the slow rhythms of the forest and its practically eternal existence. The farthest they can travel is 30 feet a year, and they really don’t need to be able to travel any farther than that. If the environment around a tree changes because the tree dies, all a weevil has to do is make it to the next tree and continue nibbling around there in the rotting leaf litter. If you find weevils, you can be sure the forest has a long uninterrupted history. If the forest was cleared in the Middle Ages and later replanted, you won’t find these insects, because it would simply have been too far for them to walk to the next old forest.

With their annual leaf fall, the beeches created an alkaline humus that could store a lot of water. In addition, the air in this little forest gradually became moister, because the leaves of the growing beeches calmed the air by reducing the speed of the wind blowing through the trunks of the pines. Calmer air meant less water evaporated. More water allowed the beeches to prosper, and one day they grew up and over the tops of the pines. In the meantime, the forest floor and the microclimate had both changed so much that the conditions became more suited to deciduous trees than to the more frugal conifers. This transformation is a good example of what trees can do to change their environment. As foresters like to say, the forest creates its own ideal habitat.

Conifers give off terpenes, substances originally intended as a defense against illness and pests. When these molecules get into the air, moisture condenses on them, creating clouds that are twice as thick as the clouds over non-forested areas. The possibility of rain increases, and in addition, about 5 percent of the sunlight is reflected away from the ground. Temperatures in the area fall. Cool and moist—just how conifers like it. Given this reciprocal relationship between trees and weather, forest ecosystems probably play an important role in slowing down climate change.45

A biologist from Leningrad, Boris Tokin, described them like this back in 1956: if you add a pinch of crushed spruce or pine needles to a drop of water that contains protozoa, in less than a second, the protozoa are dead. In the same paper, Tokin writes that the air in young pine forests is almost germfree, thanks to the phytoncides released by the needles.56 In essence, then, trees disinfect their surroundings. But that isn’t all. Walnuts have compounds in their leaves that deal so effectively with insects that garden lovers are often advised to put a bench under a canopy of walnuts if they want a comfortable place to relax in the garden, because this is where they will have the least chance of being bitten by mosquitoes. The phytoncides in conifers are particularly pungent, and they are the origin of that heady forest scent that is especially intense on hot summer days.

In a forest that has been left to its own devices, the genetic makeup of each individual tree belonging to the same species is very different. This is in contrast to people, who are genetically very similar. In evolutionary terms, you could say we are all related. In contrast, the individual beeches growing in a stand near where I live are as far apart genetically as different species of animals.

If climatic conditions change, the first individuals to die will be those that have the hardest time dealing with the new status quo. A few old trees will die, but most of the rest of the forest will remain standing. If conditions become more extreme, one tree species could even be decimated without this being the end of the forest. Usually, a sufficiently large number of trees remain to produce enough fruit and shade for the next generation.

There is a scientific observation that speaks to this: the blood pressure of forest visitors rises when they are under conifers, whereas it calms down and falls in stands of oaks.

What organic farms are to agriculture, continuous cover forests with careful selective cutting are to silviculture. In these forests (called Plenterwälder in German), trees of different ages and sizes are mixed together so that tree children can grow up under their mothers. Occasionally, a tree is harvested with care and removed using horses. And so that old trees can fulfill their destinies, 5 to 10 percent of the area is completely protected.