The Hidden Life of Trees

…is the title of a book by Peter Wohlleben, with an enticing subtitle “What they Feel, How They Communicate: Discoveries from a Secret World.” Wohllenben, by profession a forester in Germany, shares his tree knowledge in a lyrical, enthusiastic, approachable way. He waxes eloquent on how trees react/adapt to changes in the environment, and then communicate this information to other trees. First published in German in 2014, and then translated into English in 2016, this best seller popularized the fact that trees communicate with other trees.

Naturalists have been criticized for attributing human-type consciousness and emotions to animals. Wohlleben takes it further, in describing tree actions in animalistic terms: smell, touch, taste, even as far as making noises that other trees might sense (?!?). He writes of trees experiencing pain, having memory, and being active parents to their seedlings.

Mainstream scientists have been criticized for not attributing intent, ability, consciousness and emotions to other species. For animals, these arbitrary divisions have been repeatedly refuted: complex problem solving, use of tools, language (or minimally, communication with intent), a sense of self, the ability to mourn the dead, and so on. Even if we now accept these attributes for some animals, is it plausible to postulate the same for plants? Are trees conscious? Worded differently, are plant actions driven by decision or reaction? By memory, or built into DNA?

Two spruce trees on Glendale Avenue, probably planted
when the house was built. On south side, and so
provide shade to keep the house cool in summer.

Part of what has changed the way we think of trees is an understanding that dozens of fungi species form collaborations with trees at the roots. In exchange for sugar, a product of the plants’ photosynthesis, the fungi help gather water, phosphorus and nitrogen, and of greater interest, create networks with other trees of the same or other species. The networks, fancifully referred to as the ‘wood wide web’ allow large trees with direct access to sunlight to subsidize smaller trees that are attempting to grow despite the deep shade of the forest understory or the drier soil at the edge of the forest.  

Wohllenben goes farther with the idea of cooperating trees, citing evidence that in response to a certain amount of leaf or branch damage, the tree changes it chemical make-up to become less appealing to whatever is eating it, perhaps by increasing the tannic acid content of leaves, and then somehow conveys the change to neighboring trees of the same species. One communication venue is that damaged trees release volatile chemicals into the air that are taken up by other trees.

The theory here is that trees do better as part of a forest rather than in isolation. In summer, less sunlight reaches the ground, preserving the cool, damp, deep shade microclimate that such forest trees prefer. In all seasons, forest trees collectively protect each other from buffeting winds. When large trees finally succumb to storm or insect damage, fire, or even old age, replacement trees are already part of the understory growth, ready to fill in gaps.

Does Wohlleben think trees possess a form of consciousness? “I don’t think trees have a conscious life, but we don’t know,” he says. “We must at least talk about the rights of trees. We must manage our forests sustainably and respectfully, and allow some trees to grow old with dignity, and to die a natural death.” In rejecting the confines of the careful, technical language of science, he has succeeded more than anyone in conveying the lives of these mysterious gigantic beings, and in becoming their spokesman.

Aborists do not all agree with these claims of collaboration. From an article in the March 2018 issue of Smithsonian Magazine: “Stephen Woodward, a botanist from the University of Aberdeen in Scotland, warns against the idea that trees under insect attack are communicating with one another, at least as we understand it in human terms. ‘They’re not firing those signals to anything,’ Woodward says. ‘They’re emitting distress chemicals. Other trees are picking it up. There’s no intention to warn.’” Other plant scientists conclude that gene-driven reactions can explain everything we know about plant behavior.

So there it is – a minority of plant researchers believe in sentient intent, while a majority take a position that evolution of communication networks does not require purposefulness. Either way, when a tree falls in a forest, other trees may not ‘know’ if it made a sound, but they know it fell.