The Hidden Life of Trees: What They Feel, How They Communicate—Discoveries from a Secret World

Wohlleben begins Chapter 18 by posing the question of how water enters—and stays—in the forest environment. He explains that since land is higher than water and all water eventually drains down towards rivers and the ocean, the continents would dry out if it wasn’t for consistent precipitation. The author continues by explaining to the reader how trees help land absorb and store water. He writes that the tree canopy “intercepts” some rainfall, which evaporates again and will fall again over other land. He adds that when trees “transpire” in summertime, exhaling moisture through their leaves, this moisture evaporates into clouds which will further add to inland rainfall. Wohlleben explains that it is these phenomena that allow rainfall in places such as the Amazon basin to be “almost as heavy thousands of miles inland as they are on the coast” (106). This is why the author compares the forest to a water pump for land ecosystems.

Wohlleben describes conifer trees’ unique relationship with the weather. He explains that conifer needles contain terpenes, a chemical substance they evolved as a pest deterrent. However, terpenes substance also encourages condensation and so prompts larger clouds to form over conifer forests than other locations. In turn, these large clouds produce more rainfall, and reflect sunlight or block sunlight, keeping the ecosystem below cool and damp. Wohlleben adds that forests will surely play a large role in strategies to mitigate climate change.

Wohlleben discusses other water systems that are interconnected with the forest such as groundwater springs and streams, where the cool, flowing water is an ideal habitat for freshwater snails and salamanders. After a tree dies and falls into these streams, it can create pools of water that are ideal for many animals to live in. The slow movement of water also gives decomposer bacteria “more time to break down harmful substances” (110). The presence of beavers, who fell trees, also encourages the formation of ponds and wetlands where trees like alders and willows will thrive.

Wohlleben begins Chapter 19 by arguing that the perception of the forest as a place where all beings live in a “delicate balance” and contribute to one another’s survival is not true. Instead, he writes that all forest species are “basically ruthless” and try to take whatever resources they need to survive (113). However, the author explains that if a species became too “greedy” they would exhaust the supply of the resources they need to live. Wohlleben argues that this is why forest species have adapted behaviors that protect the resources they rely on, such as a jay burying more nuts than they could eat, which allows more trees to grow.

Wohlleben then compares the forest to a grocery store or warehouse full of nutrition for the animals who live there. He describes how woodpeckers make holes in trees in spring time in order to drink the nutritious sugary liquid from their trunks. The author notes that trees can survive this damage, and therefore remain a resource to the woodpeckers in the future, as long as the birds do not make too many holes at once.

Wohlleben examines how aphids’ parasitic relationship with trees produces food for other forest animals. As aphids suck proteins out of tree leaves, they leave behind a sugary water residue for ants, bees, and ladybugs to eat. Gall midges and wasps also rely on tree leaves to pupate, and caterpillars eat leaves and needles completely and can cause significant damage to trees during caterpillar population explosions. Butterflies and moths can also experience population explosions, which are more common in “commercial forest monocultures” than undisturbed forests (117). He notes that these populations are usually overtaken by viruses which lower them back to normal levels.

Wohlleben continues his chapter by exploring other species’ reliance on trees as a source of nutrients. These include the bark beetle (and the parasitic fungi that help them), herbivores such as deer, and the honey fungus mushroom. Even plants such as Pinesap and Small cow wheat can infiltrate the tree roots’ connections with beneficial fungi in order to feed on their nutrients. Young trees are very vulnerable to predation until their trunks are at least four inches in diameter. However, deer may feed on tree bark if they are starving. Wohlleben concludes by reminding the reader that if a tree has grown slowly in an undisturbed forest environment, then it will be more resilient to all these challenges than one planted in a commercial forest.

Wohlleben writes that old, established trees can function as “community housing projects” for the many forest animals who reside in them. He explains that martins, birds, and bats love old, thick trunks for their insulating properties. He writes that woodpeckers usually begin the process of transforming a tree into an animal home. In conjunction with wood-eating fungi, woodpeckers make holes in healthy trees which expand over time as the birds perform “renovations” every year (126). The fungi, too, continue to erode the wood until these spaces are too large and exposed for the woodpecker family to live in. Once the woodpeckers vacate the tree other animals, such as the nuthatch bird, bats, and owls, will come to take its place. Wohlleben clarifies that these activities will almost certainly kill the tree, however if it can heal its external damage it may be able to extend its life.

As the tree trunk rots, its community of dependent animals and organisms expands greatly. These creatures include wood ants, fungi, beetles, bats, owls, and dormice. The author reiterates the important role that dying and dead trees play in the forest ecosystem by reminding the reader of how much life they support as they die. Wohlleben concludes his chapter by arguing that this biodiversity “stabilizes the forest ecosystem” (130).