A year and a half ago, I had a short exchange on social media with a lady who thought that plants could think, talk, smell, taste and listen exactly as do. She wondered if her plants approved of her taste in music. If only she could understand what they were trying to tell her. I tried to explain that although plants are complex organisms which react to stimulus in sophisticated ways that we may never completely understand, but we can’t take terms applicable to animals and whimsically apply them to plants defying the very precision with which those terms are used in science. Imagine if bats were to think that humans answering to their names is echolocation, it would be similar. She would have none of it and dismissed me as a hopeless ignoramus - it didn’t matter that although I’m a computer scientist and not a biologist, I have a fairly good understanding of the basics of biology. She, on the other hand, had recently read Peter Wohlleben’s book “The Hidden Life of Trees”.

This week, I picked up this book to read, and after only a few pages, I was able to understand why she had such force in her conviction.

Peter Wohlleben is a forester in Germany, and the book is purportedly written so that laymen can appreciate the beauty and complexity of trees. Trees are very intruiging and don’t get the same amount of attention in science writing as animals do, and more science writing about trees is welcome. Trees are complex and fascinating organisms and much is not known about them.

Wohlleben, however, is determined to present trees as human beings with barks and leaves. Anthropomorphism, unfortunately, is a fetish throughout the book, and becomes self defeating. Trees are fascinating and complex organisms, and they deserve our attention and respect for what they are, not for being like us and not for being useful to us.

In the beginning Wohlleben, by enclosing the word smell in quotes, makes some distinction between trees actually having animal sense or having something akin to it.

As the chemical drifts through the air and reaches other trees, they “smell” it and are warned of the danger. Even before the giraffe reaches them, they begin producing toxic chemicals. Insect pests are dealt with slightly differently. The saliva of leaf-eating insects can be “tasted” by the leaf being eaten.

Smell isn’t merely the the chemical process of detection of a molecule. A large part of the sense is the cognition of it in which the brain transforms the detection of a molecule into something that we call a sense. If cognition weren’t a part of it, one could well argue that gas chromatographs can smell just like humans can. Popular science books often use anthropomorphic terms in a metaphorical sense for easy reading. There is nothing wrong in it as long as it is clear that the usage is metaphorical and not literal.

However, it isn’t long before he ceases making such distinctions.

For if they can identify saliva, they must also have a sense of taste.

He proceeds in the same literal manner and writes.

Thanks to selective breeding, our cultivated plants have, for the most part, lost their ability to communicate above or below the ground–you could say that they are deaf and dumb–and therefore they are easy prey for insect pests.

A numbered reference is provided in the above. It might have been helpful if footnotes were provided at the bottom of each page, however, as with many other books, all the notes were clubbed together and relegated to the very end of the book. One usually assumes that a popular science book would refer to peer reviewed articles, however, in the case above, Wohlleben uses a link to a blog. This is a repeated theme in the book, where he even refers to corporate talks instead of peer reviewed science.

Furthermore, the reference provided above deals specifically with corn, but Wohlleben is happy to extend this to all trees without a word of caution for his readers.

Wohlleben goes even further to suggest that plants have nerves, something that is not in the realm of the science that we know.

The electrical signals travel via a form of nerve cell at the tips of roots

Wohlleben proposes that plants can hear because they respond to vibrations. One wonders if Wohlleben would say that humans can hear earthquakes because humans tend to change their behaviour when they sense vibrations of the ground at the frequency and amplitude typical to earthquakes.

Whenever the seedlings’ roots were exposed to a crackling at 220 hertz, they oriented their tips at that direction. That means that grasses were registering this frequency so it makes sense to say they “heard” it.

He continues, that since we, as humans, are able to speak, perhaps plants can speak too, although science hasn’t found it out yet.

Plants communicate by means of sound waves? That makes me curious to know more, because people also communicate using sound waves. This might be a key to getting to know trees better? To say nothing of what it would mean if we could hear whether all that was well with beeches, oaks, and pines, or whether something was up. Unfortunately, we are not that far advanced, and research in this field is just beginning. But if you hear a light crackling in the forest next time you walk in the forest, perhaps it won’t be just the wind…

He writes that plants are capable of informed relationships like friendship. While symbiosis is a well documented phenomenon in science, it is different from friendship, but Wohlleben doesn’t dwell on the differences.

I’ve already mentioned that beeches are capable of friendship and go so far as to feed each other. It is obviously not in a forest’s best interest to lose its weaker members. If that were to happen, it would leave gaps that would disrupt the forest’s sensitive microclimate with dim light and high humidity. If it weren’t for the gap issue, every tree could develop freely and lead its own life. I say “could” because beeches, at least, seem to set a great deal of store by sharing resources.

The references gets even more patchy where he cites personal communications with fellow foresters to support the his claims where he passes of a hypothesis as an established fact.

However, colleagues from Lubeck in northern Germany have discovered that a beech forest is more productive when the trees are packed together. A clear annual increase in biomass, above all wood, is proof of the health of the forest throng.

When trees grow together, nutrient and water can be optimally divided among them all so that each tree can grow into the best tree it can be. If you “help” individual trees by getting rid of their supposed competition, the remaining trees are bereft. They send messages to their neighbours in vain, because nothing remains but stumps. Every tree now muddles along its own, giving rise to great differences in productivity. Some individuals photosynthesize like mad until suger positively bubbles along their trunk.

This line of argument is continued further where he passes off reproduction as “tree love”.

Whether tree love happens every spring depends on species. Whereas confiers send their seeds out into the world at least once a year, deciduous trees have a completely different strategy. Before they bloom, they agree among themselves. Should they go for it next spring, or would it be better to wait a year or two?

Not only does Wohlleben attribute human sensations to trees, he is also somehow able to figure out what is more difficult to endure for the tree.

THIRST IS HARDER for trees to endure than hunger, because they can satisfy their hunger whenever they want.

It is not to say that Wohlleben is writing fiction altogether. Some of what he writes is quite enlightening. However, the biggest pitfall is that he presents a lot of his own view and hypothesis along with scientific facts, but he doesn’t offer any aid for the reader to distinguish between the two. By this stage, I was confused enough not to know if this was something I could rely upon, or if it was only the opinion of a non-specialist. Especially in instances like this where no references were provided:

The process of learning stability is triggered by painful micro-tears that occur when trees bend away in the wind, first in one direction and then in the other. Wherever it hurts, that’s where the trees must strengthen its support structure.

Wollheben doesn’t leave any stone unturned to humanize the trees and suggests that they can scream, if only we could hear them!

… when trees are really thisty 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.

To support this hypothesis, he cites a non peer reviewed page from the website of Swiss Institute of Forest, Snow and Landscape. I would like to highlight that he doesn’t cite any peer reviewed science in plant physiology here:

Scientists at the Swiss Federal Institute for Forest, Snow and Landscape Research recorded the sounds, and this is how they explain them: Vibrations in the trunk when the flow of water from the roots to the leaves is interrupted. This is purely a mechanical event and probably doesn’t mean anything. And yet?

However, the observations of the scientists do not agree with his claim that plants scream, so he goes on to provide provide further justification:

We know how sounds are produced, and if we were to look through a microscope to examine how humans produce sound, 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 vibration–they could be cries of thirst. These trees might be screaming out a dire warning to their colleagues that water levels are running low.

I would have had no objections if he hypothesized that plants were communicating with each other. However, he chooses to deliberately overemphasize “sound”, “vocal cords” and “screaming” to make anthropomorphize the plansts. One would wonder, going by the same logic, if Wohlleben also thinks that the vibrations in our pulse are actually screams of our heart in a very literal sense?

By this time, one is not surprised to see statements of comparison made with such imperiousness:

A break in its bark, then, is at least as uncomfortable for a tree as a wound in our skin is for us.

The author then suggests that plants have brains, just that no one knows. He also passes off his own hypothesis as a scientific fact. Incredible!

… but now we know that trees can learn. This means they must store experiences somewhere, and therefore, there must be some kind of a storage mechanism inside the organism. Just where it is, no one knows, but the roots are the part of a tree best suited to the task.

He then suggests that scientists are divided on whether plants can think or not. At least, this was the first time I’ve ever heard of such a thing. Scientists, if anything, are very careful not to attribute terms outside their strict scientific definition:

For some years now, a heated controversy has flared up among scientists. Can plants think? Are they intelligent?

He expresses disdain for scientists and the scientific method, perhaps, because they don’t agree with him. To me it seemed like a contradiction with the paragraph quoted above.

Right now, the majority of plant researchers are skeptical skeptical about whether such behaviour points to a repository for intelligence, the faculty of memory, and emotions. Among other things, they get worked up about carrying over their findings in a similar situations with animals and, at the end of the day, about how this threatens to blur the boundary between plants and animals. And so what? What would be so awful about that?

I got the impression that he was accusing scientists of dishonesty and dogma.

Does that mean that beings that live life in the slow lane are automatically worth less than ones on the fast track.

Perhaps Wohlleben is confusing morality for scientific fact above. Science is not in the business of determining worth, it is in the business of knowing the truth. I’m not sure why Wohlleben says that. Could it be because he is constantly mixing up science and morality in the book? It is understandable that one is surprised when Wohlleben himself starts determining the worth of some animals with respect to others.

It’s certainly true that beetle mites, springtails, and pseudocentipedes are not nearly as engaging as orangutans or humpback whales, …

It is not that I’m not against a moral stand. I myself have a moral stand and think that we need to conserve nature. Rachel Carson’s Silent Spring is a much loved book which takes a moral stand, but without relying on bad science.

Wherever Wohlleben doesn’t anthromorphize trees and draws on his expertise as a forester, it makes for interesting and enlightening reading.

In total, a fifth of all animal and plant species–that’s about six thousand of the species we know about–depend on dead wood. As I have explained, dead wood is useful because of its role as a nutrient recycler. But can it also be a threat to the forest? After all, perhaps if there’s not enough dead wood lying around, organisms might decide to eat live trees instead. I hear this concern voiced time and again by people who come to visit the forest, and there are a few private forest owners who remove all dead trunks for exactly this reason. But this is neither necessary nor a useful practice. All removing dead wood does is destroy valuable habitats, causeless live wood is of no use to organisms that live on dead wood.

Marcello Di cintio interviewed Wollheben and asked him if there was a danger anthropomorphizing. His response was “Not for the trees”. One wonders if Wohlleben was aware that his anthropomorphizing would mislead readers who may not have had a proper introduction into biology. One would be justified in in being concerned about the rise of such “ends justify the means” science writing. Science is all about evidence and truth, and science writing that divorces itself from the truth and conflates opinion with facts does grave disservice to the credibility of science.

Ecologist Susan boon writes in her review of the same book:

I want people to get excited about science—especially environmental science. But I want them to be excited about accurate science. Nature is amazing just as it is, and I don’t want to twist facts to make it seem even more amazing. As Zimmerman said: “trees are remarkable without human traits,” and as Richard Fortey wrote in his review of the book for Nature: “Trees are splendid and interesting enough in their own right without being saddled with a panoply of emotions.”

The challenge for the science writer is to generate enthusiasm based on our knowledge about (in this case) trees, while using good storytelling to draw people in, and trying to avoid “changing” facts to make them more appealing to readers.

Erin Zimmerman, a plant biologist who turned to science writing and illustration, is even more critical in her review:

The author doesn’t necessarily seem to be aware of the state of research in certain fields he discusses, either. He contends that we know even less about life in the soil than we do about the ocean floor or the surface of the moon and that “researchers are only peripherally interested in the thousands of species discovered so far,” having merely given them “unpronounceable Latin names.” I suspect that the entire labs devoted to studying soilborne organisms, both ecologically and for agricultural purposes, would take issue with this assertion.

The other problematic aspect of this book comes from Wohlleben’s constant need to anthropomorphize the trees he discusses. The early chapters of the book in particular are rife with trees being described as feeling affection toward one another, experiencing pain, possessing a sense of taste, and even having maternal instincts. Being colonized by symbiotic fungi, Wohlleben claims, “gives rise to positive feelings” within the tree. Some tree species are described as sociable and altruistic, while others are characterized as loners and bullies, imposing human values of positive and negative upon what are neutral traits evolved to aid in survival.

The author asks at one point why three trees growing under the same conditions should shed their leaves at different times, and he concludes that it is “a question of character” and the early shedder is simply “a bit more anxious.” Whether this is Wohlleben’s obscure way of explaining what likely amounts to individual genetic differences or whether he really thinks the individual trees have personalities is unclear, but this sort of fuzzy explanation doesn’t serve to educate the lay reader on what is known about tree physiology. These sections of the book have the feel of Wohlleben wanting very much to believe that trees are simply a sort of immobile animal, with a rich inner life and complex society, even if scientific research has been unable to demonstrate the existence of these phenomena.

Science writing can be fun and emotive without the relying on bad science. Environmental writing can be emotive and carry moral and ethical messages without the anthropomorphizing plants. The truth is stranger than fiction, and is enough to give nature writing the intrigue it needs to captivate the reader.