62 pages • 2 hours read
Peter WohllebenThe Hidden Life of Trees: What They Feel, How They Communicate—Discoveries from a Secret World
Nonfiction | Book | Adult | Published in 2015A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Chapters 1-4Chapter Summaries & Analyses
Chapter 1 Summary: “Friendships”
Wohlleben begins his first chapter by reminiscing on how he once found living remains of tree trunks in the forest where he works. He was surprised to find these tree parts still alive, since they were clearly hundreds of years old, and the rest of the trees had long since rotted into humus, or the organic part of soil formed by decomposition. Wohlleben explains that tree’s cells require sugar to stay alive, and that trees provide their cells with this necessary nutrient through photosynthesis. Since they no longer had branches and leaves, these tree stumps could not perform photosynthesis, but instead managed to stay alive because of neighboring trees, who sent nutrients to them through their root systems.
Wohlleben reports that other forestry scientists have discovered that trees can transfer nutrients from root to root using either “fungal systems” or by physically intertwining their roots together (2). To illustrate his point he compares forests to ant hills, where each member is working hard to contribute to the health of the whole “superorganism” (2). These connections are far from random or accidental. The author credits Massimo Maffei with the argument that trees “are capable of distinguishing their own roots from roots of other species and even from the roots of related individuals” (3). Wohlleben explains that trees are “social beings” because cooperation is a huge boon to their survival. These advantages include creating a microclimate, protecting themselves from extreme cold and heat, effectively storing water, and shielding themselves from stormy weather.
The author concludes his chapter by adding that these mutually beneficial connections are most likely to happen in “undisturbed” forests that have not been logged or replanted by humans. Planted trees generally have weaker connections to each other, which Wohlleben attributes to their roots being damaged upon planting and could not survive for hundreds of years the way the trees in undisturbed forest communities can.
Chapter 2 Summary: “The Language of Trees”
The author explains that trees use scent as a mode of communication. He notes that, when being eaten by an animal, trees are capable of producing toxins to repel them, since these creatures are a threat to their health. He gives the example of acacia trees in Africa filling their leaves with the toxin ethylene to stop giraffes from eating them. Wohlleben notes that this serves as communal as well as individual self-defense; the scent of toxins is carried on the wind and interpreted by other nearby trees as a sign that they, too, should produce the same toxin. This proves that trees can use scent to communicate danger and save themselves and their neighbors from animal predation.
When trees register that a pest is eating their leaves, they send electrical signals throughout the tree which travel at one third of an inch per minute. These signals are what prompt the tree to release its “defensive compounds,” which take an hour or so to affect the pest (7). Tree roots in crisis are capable of similar signaling and can tell leaves to create defensive scents. Remarkably, these scents can be very specific, since trees are capable of distinguishing different pests from each other. For example, if an elm tree registers a caterpillar’s saliva it will release a specific pheromone that attracts wasps—a beneficial pest that will kill the caterpillars, saving the elm tree. Wohlleben extrapolates that this means that “trees can match the saliva to the insect,” and therefore must “also have a sense of taste” (8). Some of tree defenses are not specialized and are not emitted as specific responses to pests. For example, oaks and willows always produce leaves that taste bitter and toxic to deter pests.
Wohlleben explains that trees can also send signals through the “fungal networks” around their roots (9). These signals may consist of electrical impulses or chemical compounds, which travel through the fungal networks to the tips of trees’ roots. The strands of these fungi grow in the soil with “unbelievable density” (10). Over hundreds of years, one type of fungus can network an entire forest, creating miles of fungal strands.
Trees also release sweet scents to attract beneficial insects. For example, fruit and nut trees create blossoms with a sweet nectar that attracts the pollinators they need to reproduce. These blossoms are brightly colored to appeal to pollinators as well. Wohlleben reiterates that trees can communicate with each other with signals that are electrical, visual, and olfactory. He then raises the question of trees communicating through sound waves and references a scientific study that showed that plant roots can “crackle” in a way that only other plants can “hear.” This kind of tree research is just beginning.
Chapter 3 Summary: “Social Security”
Wohlleben dismisses the myth that trees grow best far apart from each other. He claims that this belief stems from the forestry industry, which is focused on producing large quantities of harvestable lumber as quickly as possible. Wohlleben notes that it is true that trees from different species can compete with each other for resources, but that when trees are from the same species they will have a cooperative, not competitive, relationship.
He cites a study that demonstrated that beech trees in the same forest will photosynthesize at the same rate, thus producing the same amount of sugar per leaf, in spite of being different sizes and growing in different soil and light conditions. Scientists have attributed this to their roots and fungal networks, which can share sugar depending on which trees have surpluses or deficiencies. Wohlleben compares this reciprocity to social security systems in human communities, as it ensures that the weaker trees are provided for.
The author reiterates that “huddling together” is beneficial to trees’ health (15). He cites another study which found that, contrary to forestry convention, beech trees produce more lumber when planted closely together, with trunks only a few feet apart (16). Wohlleben addresses why strong, healthy trees would need their weaker neighbors to survive. He posits that weak trees serve the forest by helping it remain a “single closed unit” that has protection from harsh weather. He reminds us that even the strongest trees will face pests or disease throughout their lifetimes and may rely on their smaller neighbors for help during those incidents.
Chapter 4 Summary: “Love”
The author explores how different trees reproduce, noting that there are significant differences between coniferous and deciduous trees’ reproduction strategies. Conifers produce seeds at least once per year. However, deciduous trees “prefer to bloom at the same time” to ensure the forest maintains its genetic diversity (19).
Oak and beech trees suffer from grazing and foraging animals like deer and wild boar, who will hoard their highly nutritious nuts, leaving none to sprout into seedlings. In fact, it is for this reason these trees that will not reliably produce nuts each year—to starve out some of their pests, who will then decrease in population and not be able to consume all their nuts in later years when they do blossom. This strategy ensures that some of these trees’ offspring will be able to successfully grow into young trees.
Other tree reproductive strategies include relying on the wind to disperse pollen to neighbor trees. To avoid inbreeding, spruce trees, which produce both male and female blossoms on the same tree, will open them on different days, so that they can give or receive pollen to other spruces and not inbreed with themselves.
Other tree species such as the bird cherry avoid incest by testing the genetic makeup of the pollen that lands in its blossom. If it finds this pollen has come from male flowers on the same tree, the flower blocks it, as it is only receptive to other trees’ genes. This strategy ensures that the tree will only produce fruit and seeds that are healthy and able to grow. The author notes that scientists are still working to understand how this is possible.
Wohlleben writes that some tree species can also avoid inbreeding by producing all-female or all-male trees, but these trees depend on pollinators or the wind to successfully transport pollen from male trees to the receptive female trees. He concludes his chapter by reiterating that genetic diversity is an essential aspect of tree reproduction and forest health.
Chapters 1-4 Analysis
The author’s writing style in these chapters is clear and untechnical, making it easy for lay people to understand. Wohlleben’s inclusion of casual language and real-life comparisons helps engage his readers who do not have a background in forest science. While he does not claim that trees have human-like sentience or feeling, he often anthropomorphizes them to enliven his writing and make it more understandable. For example, he writes that “Conifers don’t need to worry about taking a break from blooming…” (21). When describing trees’ fungal networks, he compares their cooperative efforts to friendships: “[N]eighbors took over the disrupted task of provisioning the roots and thus made it possible for their buddies to survive” (18). Sometimes, he uses similes to create this anthropomorphic effect, as when he writes: “It’s a bit like the way social security systems operate to ensure individual members of society don’t fall too far behind” (15).
In his initial four chapters, Wohlleben introduces the theme of tree communication and cooperation. He primes the reader for his examination of tree cooperation by challenging the myth that trees always thrive in isolation, far from the reach of competitor trees. By pointing out all the benefits trees experience when they communicate and cooperate as a collective, Wohlleben prepares the reader for his detailed lesson on tree communication and how it helps maintain the integrity of the forest. By painting a clear picture of how trees communicate through sound and olfactory, visual, and electrical means, the author also helps us to further understand cooperation amongst trees. Trees usually communicate with a purpose—to survive and thrive as a unit through cooperative action—and Wohlleben uses scientific studies and comparisons to human concepts to help readers understand these natural phenomena.
Wohlleben dedicates much of this section to examining one of scientists’ more recent discoveries, trees’ fungal networks, or as many scientists now refer to it, the “wood wide web” (10). These networks prove that fungi and trees have a symbiotic relationship, since both trees and fungi benefit from these connections (10). Wohlleben aims to illuminate trees’ lives below the soil by explaining how and why they send signals to each other using this network. The author helps his readers understand these crucial fungal networks by comparing them to fiber optic internet cables, which can also send signals back and forth.
Wohlleben also touches on humans’ limited understanding of how forests function since much of trees’ lives are, as his title suggests, “hidden” from us. Wohlleben’s writing has a humble tone that acknowledges that scientists are just beginning to learn about trees’ sophisticated systems, and explain their functions and purposes. When scientists do not thoroughly understand a certain topic, for example, the bird cherry tree’s reproductive strategies, the author acknowledges it. He also notes that trees are difficult to study since their lifespans are so much longer than humans’ and that much of their activity occurs below the ground in conditions that researchers cannot replicate in a laboratory environment.
Wohlleben does, however, credit many different scientists with their findings, which hint at how much we have yet to learn about trees’ complex systems and processes. For example, by revealing that plant roots “crackle” at a decibel we cannot hear and that their leaves release scents we cannot smell, Wohlleben both humbles and fascinates the reader with trees’ everyday activities that are invisible to humans due to our own biological particularities.
