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 5-8Chapter Summaries & Analyses
Chapter 5 Summary: “The Tree Lottery”
Wohlleben explains that trees use energy to grow, and store energy in reserve so they can react promptly when insects or illnesses attack. They also must save energy for reproduction and propagation when the appropriate time of year arrives. Wohlleben explains that trees are particularly vulnerable to insect damage after they bloom. He attributes this to their low energy levels; they expend so much energy producing their blossoms that they cannot use any more to activate their chemical defenses against the insects. He notes that healthy trees will overcome this difficult part of the year, while weaker trees will die from it.
Observing trees’ blossom and nut production is not a reliable way to predict future weather patterns, since they actually reveal the recent conditions the trees have lived through. This is because trees’ blossoms are formed, and then remain dormant, throughout the previous year. Wohlleben explains that trees that are sick or dying often produce a great amount of blossoms more quickly than their neighbors in order to maximize the likelihood they will successfully reproduce before they die.
Wohlleben expands his explanations about tree reproduction in his discussion of trees’ different propagation strategies. He offers the example of beechnuts and oak acorns, which sprout immediately after falling on soil that is moist and soft, in warm spring temperatures, while other seeds can live in the soil for months or years before sprouting. Despite producing hundreds of thousands, or even millions, or seeds in their lifetimes, statistically, trees will only have one of their seeds reach maturity. Most seeds are eaten by animals or rotted away by fungi and bacteria, while a few will sprout into seedlings which do not survive for long. As such, Wohlleben writes that all tree seeds and seedlings are engaged in a kind of lottery.
Chapter 6 Summary: “Slowly Does It”
In a natural, undisturbed forest, trees take a long time to grow. Because young trees tend to grow in the shade of their parent tree, they do not receive enough sunlight to be able to efficiently photosynthesize and fuel substantial growth. Even though these trees may be decades old, many are no higher than a person, with thin trunks and branches. Wohlleben writes that growing slowly offers advantages to tree health. Their size means their cells remain small and airless, which keeps them “flexible and resistant to breaking in storms,” as well as more resilient to harmful fungi (33).
While these young trees are deprived of sunlight under the parent tree’s canopy, the parent tree offers them benefits such as nutrients and sugar which it passes to them through their root connections. When their parent tree finally dies and falls down, these young trees will receive much more sunlight and will grow quickly towards the top of the canopy. Young trees who fall behind will likely die in the shady conditions created by taller neighbor trees. Other dangers to young trees include being eaten by deer or smothered by vine plants such as honeysuckle. After a few decades, trees will reach the middle story of the forest, which generally means they will continue growing and reach their full potential.
Chapter 7 Summary: “Forest Etiquette”
The author begins Chapter 7 by comparing trees’ growth patterns to a kind of “tree etiquette” (37). He describes how straight trunks, evenly spaced branches, and symmetrical crowns give deciduous trees stability. Straight, symmetrical trees can withstand the powerful forces of wind, rain, and snow, as they divide these impacts amongst the branches, trunk, and roots to avoid being knocked over. There are drawbacks when trees don’t follow this “etiquette manual” (38). For example, curved and forked trees are in greater danger of breaking in a storm than their straight, symmetrical neighbors.
Wohlleben explains that trees’ new growth only comes from their tips. If their trunks are curved from growing on a hillside, or being weighed down by large amounts of snowfall, only their new growth can be straight. If the soil itself is moving, for example in areas of Alaska and Siberia where climate change is melting the permafrost, trees will grow at strange angles as their roots move with the ground. Scientists call this phenomenon “drunken forests,” since the trees look so disorganized (42).
At the edge of forests, trees grow differently as they try to maximize their time in the sunlight. When growing beside a lake or meadow, young trees receive the most light by growing almost horizontally, even though this makes them more vulnerable to storm damage. Wohlleben concludes Chapter 7 by mentioning conifers’ development, noting that they almost always grow straight upwards.
Chapter 8 Summary: “Tree School”
Wohlleben describes the lessons trees must learn to grow safely and successfully in the competitive and sometimes harsh forest environment. Their first lesson is to appropriately conserve and ration their use of water so they can survive periods of drought. In winter, when water is abundant, healthy trees will stockpile it, and then use these reserves when spring and early summer create warm and dry conditions.
Wohlleben notes that, somewhat counterintuitively, the trees that suffer the most dehydration during drought periods are those that usually grow in damp soil. These trees, he explains, have not learned that they must stockpile and ration water the way that trees in drier areas have. These desiccated trees are at risk of having their dry trunks break open, opening the door to parasitic fungi and bacteria preying on the tree. The author claims that trees change their behavior from surviving these experiences and become better at storing water in the future.
Trees that lean on other trees for stability will be left vulnerable if those trees are cut down. It can take years for trees to recover from losing their neighbors, since every time they bend in a new, uncomfortable way, unsupported by other trees, they suffer “micro tears” (46). They then have to send more energy to strengthen these weak and damaged locations. According to Wohlleben, this healing process greatly delays their growth since they must expend energy on these repairs rather than fuel their growth.
Wohlleben raises the question of trees’ learning and knowledge, observing that, though they don’t have brains, they do seem to be able to store knowledge and act upon it. He cites a study by Dr. Monica Gagliano in which mimosa plants, whose leaves are very reactive to stimuli, showed evidence of learning. These plants were raised in a laboratory environment and first reacted to falling water droplets by curling up in self-defense. Over time, they learned that the water droplets were not threatening, and remained open under the falling water, even weeks later.
The author concludes his chapter by providing another interesting example of recent tree research. Scientists in Switzerland have discovered that thirsty trees create sounds through vibrations in the trunk. Wohlleben hypothesizes that trees could be producing these sounds, which are not audible to humans, to try to communicate a drought warning to other trees.
Chapters 5-8 Analysis
Wohlleben’s writing style in these passages remains lively and colloquial. He personifies trees and their seeds or seedlings, infusing his subject with personality. When writing about an acorn, for example, he says that “it has no choice but to sprout” (27). He describes new seedlings with an almost paternal affection, writing “What are the youngsters’ chances of growing up and producing another generation?” (28). Wohlleben even characterizes poplar seeds as mail parcels: “Wrapped in their fluffy packaging, these seeds strike out via airmail in search of new pastures” (30). He again uses personification when explaining trees’ relationships with their own seedlings, writing that “their own mothers do not approve of rapid growth” (32) and that “you might even say they are nursing their babies” (33).
Wohlleben continues to include illuminating examples for the reader, such as his quite remarkable calculations which demonstrate tree propagation statistics. When Wohlleben compares seedlings’ chances of growing into an adult tree to “winning the lottery,” he explicates these statistics with the example of a Beech tree (29). He estimates that a Beech which lives to 400 years old would produce nuts about 60 times in its life, dropping about 1.8 million beechnuts in total, and the one seedling which grew into a healthy adult tree would be the lottery winner.
In these chapters the author also introduces the theme of evolutionary strategies. He points out that different tree species have evolved different reproductive and propagation strategies and that, while all trees produce huge quantities of nuts or seeds in their lifetimes, they can function quite differently. For example, these nuts and acorns must transform into seedlings quickly, since they are always in danger of being eaten by foraging animals. These fast-sprouting seedlings have no defensive mechanisms against parasitic bacteria or fungi, since they have not evolved to last long on the forest floor.
Wohlleben then contrasts this strategy with that of other tree seeds, which are able to remain viable for months or even years after falling from their parent tree. Bird cherry seeds, for example, are capable of remaining dormant for up to five years until they are in appropriate conditions to sprout. By explaining such different types of reproductive strategies, Wohlleben helps his readers understand more about the differences in trees’ evolution.
He also includes burgeoning tree research in these passages and offers his own commentary on their findings. For example, when discussing how bird cherry trees know how to only use other trees’ pollen, Wohlleben writes that “You might say that we, too, experience the physical act of love as more than just the secretions of neurotransmitters that activate our bodies’ secrets […]” (23). When the author discusses dehydrated trees’ vibrations he comments, “When I think about the research results […] it seems to me that these vibrations could indeed be much more than just vibrations—they could be cries of thirst” (48).
