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 21-24Chapter Summaries & Analyses
Chapter 21 Summary: “Mother Ships of Biodiversity”
Highly specialized and minute ecosystems that can exist on trees. Wohlleben cites a study which found over 2,000 insects from 241 species living on one old-growth tree alone. Additionally, trees with tiny pools or cavities of water begin to function as wetland ecosystems for animals that require these conditions such as small flies, beetles, and the bumblebee hoverfly.
Wohlleben explains that when trees die all of the nutrients they have taken from the soil is slowly released back into the ground, where it is extremely useful to the younger trees. The author writes that fungi, bacteria, and insects that specialize in decomposition quickly colonize the tree in a “culinary relay race” that biodegrades the tree into humus (132).
He continues his chapter by debunking the myth that allowing dead wood to remain in a forest puts living trees under threat of being colonized by decomposers. He explains that this belief is completely unfounded; the types of fungi, bacteria, and insects that break down dead trees could never harm a living one since their characteristics are too different. Further, he argues that removing dead wood from forests for this purpose is detrimental to those ecosystems since creatures require these habitats and their work adds nutrients to the forest soil.
Chapter 22 Summary: “Hibernation”
Wohlleben discusses deciduous trees’ seasonal cycles of work and rest, which he compares to a bear’s hibernation. He notes that these trees have a maximum capacity for nutrient storage, so at some point in late summer or early autumn when they have reached this potential, they will simply stop photosynthesizing. They then transfer nutrients from their leaves to their trunks and roots. This includes chlorophyll, which gives leaves their green color. With this element gone, leaves appear red, yellow, or brown, and Wohlleben writes that these colors serve a purpose too: their bright colors signal to aphids that they are healthy and therefore not a good choice for aphids to colonize over the winter. Another way deciduous trees prepare for winter is to decrease the amount of water inside their trunks. This is to avoid their water content turning to ice during the winter, which could cause their wood to break open.
In contrast, conifer trees keep their needles over the winter. They avoid damage from freezing temperatures by coating their needles with wax and filling them with an anti-freeze substance. This prevents the tree from transpiring its moisture out of its needles and dying of dehydration when it can’t access water in the frozen ground.
Wohlleben reveals that conifers predate deciduous trees by about one hundred million years, making leafy trees’ evolutionary adaptations relatively recent in comparison. The author hypothesizes that deciduous trees have gained a significant advantage in developing their ability to grow and lose leaves, since their bare branches avoid catching the high impact of winter winds, snow, and ice. These hazards, which affect conifers much more than deciduous trees, can easily end a tree’s life. Growing and dropping leaves also allows trees to “excrete waste” since they put substances they do not want into their leaves before they fall (142).
Within the deciduous tree family, distinct species manage their nutrition in different ways. Alders, Ash, and Elders will drop green leaves which contain chlorophyll and simply produce more the next year, while other species such as the oak will take any chlorophyll back from its leaves and only discard them when they are brown. Wohlleben mentions the three conifers which are exceptions to the rule: the larch, the dawn redwood, and the bald cypress, which lose their needles in the autumn and regrow new ones in the spring. Other conifers only shed old needles that need replacing, which can make them look “somewhat sparse” during the winter months until they regrow replacement needles in the spring (146).
Chapter 23 Summary: “A Sense of Time”
Wohlleben argues that if trees behave differently depending on the season, they must have a “sense of time” (147). He notes that trees seem to be able to “count” how many warm days they have experienced, since scientists have discovered that fruit trees will begin to form leaves after a certain number of spring-like days. Trees also tell time by registering how much light they receive each day. Wohlleben admits that scientists are still trying to understand how it is possible for a leafless tree to sense light, but he hypothesizes that it is their new buds that have this ability. He explains that tree buds are simply rolled up leaves with scales for protection.
These abilities also extend to tree nuts, which must not sprout too early and become damaged by winter conditions or grazing animals. Depending on where they end up, seeds must register the warmed temperature of the soil or the increase in light on the soil surface in order to sprout at the appropriate time.
Chapter 24 Summary: “A Question of Character”
In this passage Wohlleben argues that trees each have their own “character” (151). He points out that even when factors such as tree species, weather conditions, soil type and location are exactly the same, trees will behave differently from each other. These differences can be visible to even a casual observer. For example, you might see which tree drops its leaves first in an effort to prepare for winter early.
Wohlleben develops his argument about trees’ unique characters by noting that only some trees take advantage of gaps in the forest understory to grow large branches from their lower trunks. This growth poses a risk to their long-term health, since once the canopy shades these lower branches they will die and break off, leaving the trunk dangerously exposed to fungi. Wohlleben attributes this growth to a kind of decision-making process that reveals the tree’s character. Either it is a risk-averse tree that simply continues growing upwards, or a more bold tree that will grow a new branch to try to exploit short term sunny spots despite the long-term risk.
Chapters 21-24 Analysis
In these passages Wohlleben expands his theme on the interconnected forest food web. Wohlleben makes it clear to the reader that forests cannot thrive without creatures who specialize in decomposing dead wood. He provides many examples of these forest decomposers, which he explains include species of bacteria, fungi, and insects. According to the author, about one fifth of all plants and animals on earth live on dead wood! Sharing this statistic helps impress upon the reader the huge role dead wood plays in the planet’s ecosystems.
To help the reader visualize how this decomposition occurs, the author gives examples of these decomposition specialists and how they behave. Wohlleben provides the example of the stag beetle, which he says spends years of its life as a larvae, digesting the roots of deceased trees. In doing this special task, these beetle larvae process these roots and make their nutrients available to living plants. Wohlleben notes that this type of beetle only lives on the soil’s surface during its very brief adulthood, during which time it mates and then promptly dies. The majority of its life is spent fulfilling the essential task of dead root decomposition. The author explains that another important decomposer is bracket fungus, which consumes cellulose, a certain element in tree wood. Wohlleben shows how these fungi are extremely important decomposers. He also helps the reader imagine the intense competition amongst decomposer fungi by reporting that they can even wall off their own dead wood “territory” with polymers (134).
Wohlleben draws on the parallels between trees and bears to explain deciduous trees’ cyclical patterns of growth and dormancy, continuing his pattern of engaging the reader through analogy. He writes that, “The grizzly bear is a good candidate for comparison, because it follows a similar strategy to trees. In summer and early fall it lays down a thick layer of fat it can live off all winter. And this is exactly what trees do as well” (136). This comparison helps readers understand that, like bears, trees must also “eat” (by converting sunlight to sugars) in order to build up stores of nutrients which will enable them to survive through the winter. It also serves to make trees seem less abstract and mysterious and more sentient and relatable to the reader.
Wohlleben also engages the reader by providing a personal anecdote to demonstrate how trees each have their own character. He paints a picture of three oak trees which grow closely alongside each other in a local village where he lives. He then describes for the reader their different characteristics, personifying one tree as “anxious” but “sensible” for losing its leaves early in the year, and the other trees are “bolder” for keeping them longer (152). Wohlleben makes it clear that these differences occur even though all the other conditions affecting the trees are identical. This story helps Wohlleben support his argument that trees have individual approaches to challenge, and helps the reader envision trees’ different characters.
