The Hidden Life of Trees: What They Feel, How They Communicate – Discoveries from a Secret World by Peter Wohlleben is an eye-opening read that will have you looking at the natural world in a completely new light. If you took high school biology, you probably learned that one characteristic of plants is that while they’re alive, they are static creatures. We were told that although they adapt to their environment, they live at a standstill in the same place for their entire lives. And they certainly aren’t communicators. Well, as you’ll learn in The Hidden Life of Trees Key Takeaways, trees are actually dynamic, social, and incredibly complex creatures. The Hidden Life of Trees provides an entertaining deep dive into the alien world of trees.
The Hidden Life of Trees Key Takeaways
Key Takeaway #1: Trees live on a completely different time scale than humans
I’m just going to go ahead and assume that if you’re reading this post, you’re a human being (if you’re not, please contact me). As a human being, it’s only natural to view life and Earth through a human timescale. But if you think about that deeply for a second, you realize how biased that view is. Obviously the other forms of life on Earth don’t conform to a human timescale. And this bias is part of the reason we don’t fully appreciate the complexity of trees:
One reason that many of us fail to understand trees is that they live on a different time scale than us. One of the oldest trees on Earth, a spruce in Sweden, is more than 9,500 years old. That’s 115 times longer than the average human lifetime. Creatures with such a luxury of time on their hands can afford to take things at a leisurely pace. The electrical impulses that pass through the roots of trees, for example, move at the slow rate of one third of an inch per second.
Our biased view of the timescale of other life forms leads us to think of trees (and other plants) as glorified rocks:
The main reason we misunderstand trees, however, is that they are so incredibly slow. Their childhood and youth last ten times as long as ours. Their complete life-span is at least five times as long as ours. Active movements such as unfurling leaves or growing new shoots take weeks or even months. And so it seems to us that trees are static beings, only slightly more active than rocks.
Key Takeaway #2: Trees are social creatures
This was perhaps the most astonishing takeaway for me from The Hidden Life of Trees. I had no idea how social trees are. And it appears that the social relationships are not “random”. There seem to be forms of altruism, loyalty, and other supposedly human character traits present in trees.
The trees in a forest care for each other, sometimes even going so far as to nourish the stump of a felled tree for centuries after it was cut down by feeding it sugars and other nutrients, and so keeping it alive. Only some stumps are thus nourished. Perhaps they are the parents of the trees that make up the forest of today. A tree’s most important means of staying connected to other trees is a “wood wide web” of soil fungi that connects vegetation in an intimate network that allows the sharing of an enormous amount of information and goods. Scientific research aimed at understanding the astonishing abilities of this partnership between fungi and plant has only just begun.
We’re only scratching the surface of how social trees (and other plants are). The best analogy to understand the social nature of trees is to think of a forest like an insect colony:
Forests are superorganisms with interconnections much like ant colonies.
[…]
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.
Thinking of old-growth forests in this manner provides a better context for what happens when even portions of a forest are damaged due to logging, fires, or other human-caused disasters.
Key Takeaway #3: Agriculture has produced “dumb” plants
Throughout The Hidden Life of Trees, the author makes numerous references to the study of “forestry”, which in his opinion, is entirely geared to the needs of the logging industry. While he applauds efforts by logging companies to be more sustainable, Wohlleben makes the key distinction that old growth forests cannot be created or maintained by a top-down human-designed approach. The various plants, insects, and animals in old-growth forests are all part of tightly linked feedback loops which are beyond (current) human understanding.
While the study of old-growth forests may seem like an unnecessary, purely academic endeavor, the implications are vast and of particular importance to agriculture. Wohlleben clearly makes this distinction:
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. That is one reason why modern agriculture uses so many pesticides.
This has implications for all of us. Plants that can’t communicate to coordinate defenses against predators (insects, birds, etc) require pesticides to survive long enough for harvesting. Pesticides and selective breeding are a large reason for cultivated fruits having a worse nutritional profile than wild fruits.
Key Takeaway #4: Trees have a sense of smell, hearing, and taste
This takeaway was astonishing to me. Obviously trees are not using words and speech like humans but they very clearly communicate with each other:
Trees, it turns out, have a completely different way of communicating: they use scent.
Beyond scent, trees also appear to have a sense of taste:
The saliva of each species is different, and trees can match the saliva to the insect. Indeed, the match can be so precise that trees can release pheromones that summon specific beneficial predators.
[…]
For if they can identify saliva, they must also have a sense of taste.
Hearing is another sense that trees appear to possess, particularly at the ultrasonic level:
When trees are really thirsty, they begin to scream. If you’re out in the forest, you won’t be able to hear them, because this all takes place at ultrasonic levels. Scientists at the Swiss Federal Institute for Forest, Snow, and Landscape Research recorded the sounds, and this is how they explain them: Vibrations occur in the trunk when the flow of water from the roots to the leaves is interrupted. This is a purely mechanical event and it probably doesn’t mean anything. And yet? We know how the sounds are produced, and if we were to look through a microscope to examine how humans produce sounds, what we would see wouldn’t be that different: the passage of air down the windpipe causes our vocal cords to vibrate. When I think about the research results, in particular in conjunction with the crackling roots I mentioned earlier, it seems to me that these vibrations could indeed be much more than just vibrations—they could be cries of thirst. The trees might be screaming out a dire warning to their colleagues that water levels are running low.
Looking at trees through a purely mechanical lens is how many scientists are able to continue to look at these amazingly complex organisms simply as “dumb plants”. The author’s callout regarding the mechanics of human speech is a great point – we (as a species) have a habit of overemphasizing the complexity and “magical” nature of humans, while relegating other creatures to the unintelligent species dustbin.
Key Takeaway #5: Trees have a sense of time
This takeaway may be controversial because time and math are generally considered human constructs. And yet:
It seems the trees 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. But warm days alone do not mean spring has arrived. Shedding leaves and growing new ones depends not only on temperature but also on how long the days are. 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. After all, they come with a kind of solar cell, which makes them well equipped to receive light waves. And this is just what they do in the summer months, but in April the leaves are not yet out. We don’t yet understand the process completely, but it is probably the buds that are equipped with this ability. The folded leaves are resting peacefully in the buds, which are covered with brown scales to prevent them from drying out. Take a closer look at these scales when the leaves start to grow and hold them up to the light. Then you’ll see it. They’re transparent! It probably takes only the tiniest amount of light for the buds to register day length, as we already know from the seeds of some agricultural weeds. Out in the fields, all it takes is the weak light of the moon at night to trigger germination. And a tree trunk can register light as well. Most tree species have tiny dormant buds nestled in their bark.
Key Takeaway #6: Forest air is incredibly healthy
This is the most actionable takeaway from the book. It turns out that the idea of clean forest air is not a myth. There are two reasons for this. The first is the ability of trees and leaves to act as air filters:
Forest air is the epitome of healthy air. People who want to take a deep breath of fresh air or engage in physical activity in a particularly agreeable atmosphere step out into the forest. There’s every reason to do so. The air truly is considerably cleaner under the trees, because the trees act as huge air filters.
In addition to filtering air, trees, like humans, are also constantly fighting off microscopic threats, including bacteria, viruses, and parasites:
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. 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.
That said, an unhealthy forest may have a negative impact on your health. Wohlleben brings up a great point when discussing our ancestors’ ability to detect safe vs unsafe environments:
And because the spruce and pines are constantly in danger of dying of thirst, they are easy prey for bark beetles, which come along to make a meal of them. At this point, frantic scent-mails begin to swirl around in the canopy. The trees are “screaming” for help and activating their arsenal of chemical defenses. You absorb all of this with every breath of forest air you take into your lungs. Is it possible that you could unconsciously register the trees’ state of alarm? Consider this. Threatened forests are inherently unstable, and therefore, they are not appropriate places for human beings to live. And because our Stone Age ancestors were always on the lookout for ideal places to set up camp, it would make sense if we could intuitively pick up on the state of our surroundings. 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. Why don’t you take the test for yourself and see in what type of forest you feel most comfortable?
This book provides even more credence to the Japanese practice of forest bathing. The Japanese government studied this in detail, designing various trials over a decade, which found improvements in all key vital signs (blood pressure, pulse, and nerve activity) as well NK cells (naturally occuring cells in the immune system which fight virally-infected cells and tumors). This has major implications for human health.
*****
The Hidden Life of Trees Key Takeaways is just a brief introduction to the worldview-shifting insights in this book. You can buy a copy of The Hidden Life of Trees on Amazon or anywhere you buy books.
Let me know what you think by contacting me here or reaching out on Twitter.
For exclusive book recommendations (not available anywhere else), please subscribe to my monthly reading recommendation newsletter.