In 2016 Peter Wohlleben, a German forestry ecologist, published a book that swiftly became a massive bestseller not just in Germany, but in Britain and the USA, too. It was called The Hidden Life of Trees: What They Feel, How They Communicate.
In the book, the author makes some pretty radical claims. Among them are that trees communicate with each other, exchange useful information, are capable of learning from experience, have a positive sociability, protect and nurture both their young and their very old, come to collective decisions about issues like population growth or fertility and feel pain.
In this view, trees are certainly sentient and possibly (although he does not say this explicitly) have consciousness – or something very like it. And from here, it is not a long step to arguing that any fixed boundary between animals and trees – even humans and trees – is arbitrary.
To reach these conclusions, Wohlleben does not evoke any kind of folkloric animism – the nymphs and spirits of classical Greece, the World Tree of the Norse sagas or the endless dark forests of fairy stories – but two very different kinds of evidence.
The first is his own experience over several decades of working in forests – 20 years with the German forestry commission, and latterly in the community-owned beech woods of Hummel, where they are working for the return of primeval forests. The evidence from this source is invariably authoritative, and often touching and beautiful.
The other source of his evidence is new scientific research, and this is where things become morecomplicated. Trees communicate, apparently, by a number of techniques. Wind-borne chemical release is one of them. When a tree is attacked by predators of various kinds – nibbling giraffes in the case of African acacias, or insect larval infestations of German beech trees, for example – it emits a chemical essence that the wind carries to other neighbouring trees and they respond by producing defences that, for instance, make their leaves less tasty to the invaders. But can such a transmission of chemicals be called communication, as it is involuntary?
Another, even more crucial communication tool used by trees is through the symbiotic relationship known as ‘mycorrhiza’ formed between trees and fungi.
Mycorrhizal fungi live in the roots of all trees (indeed of almost all plants) to the biological advantage of both. The fungi stretch out delicate threads called ‘hyphae’, which, because they are finer and further-reaching than the tree’s own roots, are able to supply the tree with nitrogen, phosphorous and other vital nutrients. Meanwhile, the tree supports the mycelium with carbon and sucrose, which the fungi needs but cannot make.
The hyphae criss-cross with each other, creating a sometimes-huge underground net that puts each individual tree in contact with its neighbours, seeming to allow for the transfer of vital resources between them. This is extraordinary and deeply fascinating, but new it is not. The existence of fungi within root systems has been known about for over a century and a half, and their mutually beneficial relationship was described by Franciszek Kamieński between 1879–1882.
The name ‘mycorrhiza’ was introduced in 1885. Oliver Rackham describes the process fully in Woodlands (2006). What Wohlleben adds is not so much new research as a vivid narrative of communication; the memorable term the ‘wood-wide web’ (which, as he makes clear, he did not originate) and a humanising language.
It is in the evolutionary interest of large deciduous trees of the sort that grow in groups (woods or forests) to maintain a full canopy. This conserves water supplies, reduces the force of winds and moderates temperature.
In an old and well-established wood, the trees have both the linking web of mycelium and often interconnected root systems, and healthy trees will provide necessary nutrients to young saplings or to trees that are, through age, disease or other circumstances, short of them. The frequency with which this happens is indeed fascinating – and the suggestion that nearby trees continue to provide sugars to the stumps of trees felled centuries ago and therefore no longer able to create their own through photosynthesis creates a rich mystery.
However, is it justifiable to describe such exchanges in terms of friendship, compassion or maternal care, as Wohlleben does? (It is always maternal, by the way – there are no father trees for the author.) Or, more generally, to speak of trees in terms of conscious emotions – fear, pain, tenderness, parental instincts panic – even if they seem to exhibit behaviours that in humans might indicate those feelings? Does the rebuilding of new bark over a ‘wound’ – such as one caused by the breaking of a branch – demonstrate that the tree is responding to pain?
Despite anthropomorphising trees, Wohlleben insists he has his limits, telling a German newspaper: “I don’t hug trees and I don’t talk to them.”
Britain’s oldest forests are predominantly oak forests, not the German beech forests that Wohlleben writes about. There are visible differences – the most obvious one is that beech forests tend to have clear floors and the beech seeds germinate under the ‘parent’ trees. This rarely occurs with oak trees – to germinate, they need to be carried away (by jays, squirrels or streams) somewhere else.
This means that Wohlleben’s talk of parenting, nurturing, education and training does not necessarily apply to British woods. All his research into chemical interactions, information exchange and ‘sociability’ has not been tested in our forests. For example, where do the flowers – such as bluebells, which grow under oak trees – fit into his observations? We do not know. Beech trees may well be damaged, if not killed, by coppicing. Hazel, however, another very common British woodland tree, appears to live longer under coppice management.
When a group of German bioscientists and other forestry experts took the unusual step of launching a public petition against The Hidden Life of Trees, on the grounds that they felt it was pseudo-science. Wohlleben responded to the criticisms by stating that all his facts are “based on science”.
I am not sure that for Wohlleben the science is the important thing: I think he deeply loves trees and wants them to be protected, nurtured, honoured. This is a good agenda but it raises more questions of its own – a central one here is what is the evidence that we, human beings, are more likely to protect, honour or nurture beings that we identify with? We are not doing very well with our own species – or with primates who are surely much easiernto anthropomorphise than trees are.
It seems to me we should protect trees precisely because they are not like us, but so very different.