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

by Peter Wohlleben

water and forests share an almost unbreakable bond. Streams, ponds—even the forest itself—all these ecosystems depend on providing their inhabitants with as much stability as they can. A good example of an organism that doesn’t like a lot of change is the freshwater snail. Depending on the species, it is often less than 0.08 inches long, and it loves cold water. They like it to be no more than 46 degrees Fahrenheit, and for some freshwater snails the reason for this lies in their past: their ancestors lived in the meltwater that drained off the glaciers covering a large part of Europe in the last ice age.

And don’t worry about that foam that sometimes forms in these pools after heavy rains. What looks like an environmental disaster is, in fact, the result of humic acids that tiny waterfalls have mixed with air until they turn into froth.

If you live in Europe, mature deciduous trees offer a very special service to help you: a short-term weather forecast brought to you by chaffinches. These rust-red birds with gray heads normally sing a song whose rhythm ornithologists like to transcribe as “chip chip chip chooee chooee cheeoo.” But you’ll hear that song only on a fine day. If it looks like rain, the song changes to a loud “run run run run run.”

Alders, for example, happily drop bright-green leaves onto the ground as though there were no tomorrow. Alders, however, usually grow in swampy, nutrient-rich soil and can, apparently, afford the luxury of producing new chlorophyll every year. Fungi and bacteria at the base of the trees recycle the discarded leaves to produce the raw materials the alders need to build chlorophyll, and all the trees need to do is take these building blocks up through their roots. They don’t even have to worry about recycling nitrogen, thanks to the symbiotic relationship they have with bacteria in nodules on their roots, which constantly provide them with all the nitrogen they need. Per year and square mile of alder forest, these tiny helpers can extract up to 87 tons of nitrogen from the air and make it available to the roots of their tree friends.53 That is more than most farmers spread over their fields as fertilizer.

conifers. I’ve given them rather short shrift so far, but there are three species that drop their leaves like deciduous trees—the larch, the bald cypress, and the dawn redwood.

As long as the trees are healthy, firs always keep ten, spruce six, and pines three years’ worth of needles,

can count! They wait until a certain number of warm days have passed, and only then do they trust that all is well and classify the warm phase as spring.55

Beeches, for example, don’t start growing until it is light for at least thirteen hours a day. That in itself is astounding, because to do this, trees must have some kind of ability to see. It makes sense to look for this ability in the leaves.

And a tree trunk can register light as well. Most tree species have tiny dormant buds nestled in their bark. When a neighboring tree dies and falls down, more sun gets in, which in many trees triggers the growth of these buds so that the tree can take advantage of the additional light.

These secret reserves can be activated at any time, and depending on the tree species, they contain a selection of defensive compounds produced by the tree. These so-called phytoncides have antibiotic properties, and there has been some impressive research done on them. 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 stinging hairs on the shed skins remain hanging in the webs and can inflict damage for up to ten years.

find. The few oaks that grow in the forest are mixed in with beeches, and only their topmost tips reach the light. In the city, however, oaks stand out in the open, where they are warmed by the sun all day long. The caterpillars love this. And as the whole “forest” in urban areas offers such perfect conditions, it’s no surprise that there are population explosions, which are a stern reminder that oaks and other species growing along the streets and between houses have to fight for their lives.

Grasses are adapted to constant grazing and are relieved that the young trees that threaten their existence are being polished off in the process. Many shrubs that would dearly love to grow taller than the grasses have developed dangerous thorns to protect themselves from the voracious beasts. Blackthorn is so vicious that its pointed protrusions persist on dead plants for years to impale rubber boots and even car tires, to say nothing of the hides and hooves of animals.

Not only do browsers break their teeth on the tough bark, but they are also revolted by the taste of its oil-saturated fibers. This oil, by the way, is the reason even green birch bark burns so wonderfully well and is great for lighting campfires. (If you’re going to try this, pull off only the outermost layer of bark so that you don’t harm the tree.)

The white color is because of the active ingredient betulin, its primary component. White reflects sunlight and protects the trunk from sunscald. It also guards the trunk against heating up in the warming rays of the winter sun, which could cause unprotected trees to burst. As birches are pioneer trees that often grow all alone in wide-open spaces without any neighbors to shade them, such a feature makes sense. Betulin also has antiviral and antibacterial properties and is an ingredient in medicines and in many skin care products.60

Species that live in social groups don’t entertain this option because every individual belongs to a community that will look after it in times of need, warn it of impending dangers, and feed it when it is sick or in distress.

quaking aspens don’t shake because they are afraid. Their leaves hang from flexible stems and flutter in the breeze, exposing first their upper and then their lower surfaces to the sun. This means both sides of the leaf can photosynthesize.