“The hidden life of trees” by Peter Wohlleben

Wohlleben’s book was originally published in German in 2015 and then translated and published in English in 2016. The book attracted a lot of mainstream interest due to Wohlleben’s “wood wide web” description of trees communicating with each other and sharing nutrients. I was aware of this at the time and I must admit the way he presented it all put me off. But I’ve now read the book and that’s only a small part of the wide range of topics he covers.

Peter Wohlleben began his career as a forester for the state of Rhineland-Palatinate in Germany but became disillusioned with the “big forestry” style of management and began managing a beechwood for the local council of Hummel. He published several successful books about forests, nature, and threats to the environment, before “The hidden life of trees”.

Working in woodland owned by the local council, Wohlleben gave guided tours and has described the necessity of translating the language of scientists into words other people can understand. This is mentioned in this nine minute interview by Fredrik Skavlan, which summarises the most well-known points of the book.

I believe it is this “translation” process which led Wohlleben to adopt some very anthropomorphic language, giving trees human characteristics. Trees “feel pain”, “learn”, and “remember”. This language is easier for people to relate to and provides excellent sound bites for press releases and interviews. But feeling pain, learning, and remembering are more than just responding to stimuli and changing state. They all require a level of awareness not just response. There is no evidence that trees have that, and it is misleading to talk as if they do.

“Learning” in particular requires the ability to absorb new information. A thermostat does not “learn” that the room is too hot. It just responds to that stimulus in a way determined by its design. The design already embodies the state of being “too hot”. The device does not learn about being too hot: its pre-existing response to that pre-defined stimulus is just triggered when it happens. This is equally true of organisms like trees which are designed by natural selection rather than electrical engineers. It’s true of biological thermostats in humans too for that matter: I didn’t “learn” when to sweat. My ancestors evolved it as a response to the stimulus of being too hot. I did learn how to use a smartphone though, by absorbing information that none of my ancestors had the chance to acquire.

As I mentioned, all this anthropomorphic language really put me off the book. There was a dose of it in an episode of “Start the week” which I caught on Radio 4 in 2018. It’s still available (and also features Ruth Pavey pitching her book “A wood of one’s own” which I reviewed last week.) It prompted another listener to buy me a paper copy. But but but, now I have actually read it, the anthropomorphic stuff falls away and we quickly get down to the substance.

The book is 250 pages of main text and an easy read: I read it in about four hours in two sittings. There are 36 short chapters, with few even 10 pages long. This creates a very episodic feel, almost like reading the collected articles of a regular newspaper column. Each chapter is focussed on one topic and although they are grouped together in broad themes, you could easily read a single chapter in isolation.

Chapter by chapter, Wohlleben displays his breadth of experience with forests and trees. I say both because his central thesis is that trees form a forest not just by standing in a group but by cooperating. Forests create microclimates and trees benefit from that, and so they have some interest in the survival of their neighbours. In the right circumstances, they will even help neighbours of other species. So a forest can act as a superorganism, rather like an ant colony.

Prof. Suzanne Simard

One dramatic example was established by Suzanne Simand at the University of British Columbia in Canada, who wrote an afterward to the book and whose research provides a lot of its scientific foundation. She tagged sugars with trace amounts of radioactive carbon and discovered that adjacent deciduous birch and evergreen Douglas fir trees pass sugars back and forth during the year depending on who has what and who needs what. Some “mother trees” use the same mechanisms to feed the saplings growing in the shade around their bases, and so they can wait until the parent trees eventually die.

It was Simand who coined the term “wood wide web” as a catchy name for the
mycorrhizal network of fungi which form underground alliances with trees. It has long been known that fungi can convert nitrogen from the air into compounds which plants need, and are able to pass them to trees via the thin fibres on their roots and in return receive sugars produced by photosynthesis up in the sunlight. Subsequent research revealed that a single fungal organism can be exchanging nutrients with multiple trees, perhaps even of different species. Since fungi are able to grow very long filaments through the soil, these networks can cover hundreds of metres.

There’s a TED talk describing her first experiments on this and then the wider picture:

As well as chapters devoted to trees themselves, some other animals are represented in Wohlleben’s book. There are some pages about beavers, with this important observation about why they build dams:

Because water levels can fluctuate wildly with the seasons, many beavers also build dams, blocking streams and turning them into large ponds. Beaver ponds slow the flow of water from the forest, and extensive wetlands form in the areas around the dams. Alders and willows like to grow here; beeches, which cannot stand having wet feet, die off. But the upstart trees in the feeding zone around the lodge don’t get to grow old, for they are the beavers’ living larder. Although beavers damage the forest around them, they exert a positive influence overall by regulating water supplies.

There are a few mistakes that I noticed. Coppice wasn’t a favoured management style because the medieval poor couldn’t wait for trees to grow: it was favoured because pole sized stems are easier to work, especially without powered machinery. That sort of thing. Compare that with the breadth of knowledge beyond the immediate practice and ecology of forestry displayed by a figure like Oliver Rackham.

The passage below also stood out, in contrast to the emerging consensus that herbivores and their predators have a huge rule in shaping forest ecosystems over time. Wohlleben seems unaware of this idea which motivates many of the moves towards rewilding and the reestablishment of these dynamic ecosystems:

A forest would have no problem doing without its larger inhabitants. Deer, wild boar, carnivores, and even most birds wouldn’t leave any yawning gaps in the ecosystem. Even if they were all to disappear at once, the forest would simply go on growing without many adverse effects. Things are completely different when it comes to the tiny creatures under their feet.

In 2018 an illustrated edition of the book was published, with less of the original text but lavish and beautiful photographs of tree and forests. A coffee table book, but one with more substance to its text than a lot of large format books of tree pictures. So perhaps a good choice as a carefully chosen gift to entice someone into the subject once they want to explore beyond the photographs.

All in all, once I got past my initial issues with the anthropomorphic language, I enjoyed the full, unillustrated edition of “The hidden life of trees”. It’s a book with a particular message about the importance of the mycorrhizal network and all its various consequences, but it’s also a worthwhile collection of forestry facts and experiences.


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