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 29-32Chapter Summaries & Analyses
Chapter 29 Summary: “Destination North!”
Wohlleben explores how trees can “travel” by producing seeds capable of being carried by the wind. He explains that there is an evolutionary tradeoff for seeds that are light enough to be airborne. Trees such as poplars and willows have evolved tiny, lightweight seeds with hairs that help them float on the wind for long distances. However this prevents them from being able to contain nutritional “provisions” within their seeds and so they are more vulnerable to dying of hunger or thirst (186). The author contrasts this with seeds from birch, maple, and hornbeam trees which are too laden with these provisions to fly on the wind, and so they equip their seeds for flight in a different way. Wohlleben explains that these tree species have evolved wing-like features that, if caught in a breeze, have the potential to travel for up to a mile. Wohlleben explains that pioneer species with seeds that can fly are excellent at colonizing new areas, even after natural disasters such as volcanic eruptions.
The author continues by describing how the heaviest tree seeds, such as oak acorns and chestnuts, cannot be carried by the wind at all. Wohlleben argues that this is why these seeds “enter into an alliance with the animal world” (187). Because these tree seeds contain so many nutrients, animals such as mice, squirrels, and jays will be sure to take them to various hiding places in the forest, thus enabling them to travel to new locations. However, because these animals may forget where they buried these seeds, or indeed do not survive long enough to retrieve them, the seeds have the opportunity to sprout in their new place. Jays in particular are known to move tree seeds the farthest since they can fly a few miles away before burying them.
Wohlleben describes how historically, human activity such as farming and deforestation has had a dramatic influence on European beech forests’ ability to expand to locations where they could thrive. Other European trees, such as the silver fir, migrate very inefficiently because these seeds do not fly well and are more likely to be eaten than buried by birds. He continues by explaining that while beeches are very dominant in European forests, they do not grow well elsewhere because they require cool summers, warm winters, and can use water frugally. He concludes this chapter by predicting that as the climate continues to warm, beeches will die out in southern Europe and focus on growing northward.
Chapter 30 Summary: “Tough Customers”
Wohlleben explores how trees adapt to changes in their environments. He notes that because trees live for so long they are not a species that can evolve quickly, such as fast reproducing animals like mice or flies. He argues that trees navigate change through “behavior and genetic variability” (196). Wohlleben shows that individual trees can adapt to certain conditions by describing how tree seeds can activate certain genes depending on the weather and soil they are in. As discussed in previous chapters, adult trees can also learn from their experiences and change their behavior. For example, spruces are accustomed to living in water-rich areas, however if they survive a drought they are more frugal with their water use in the future.
Tree genetics are far more diverse than human genetics. As such, even trees within the same species can contain genes that give them certain strengths or weaknesses such as resilience to insects, cold, heat, or drought. According to Wohlleben, when climate changes occur the individual trees with genetics that are not geared towards those conditions die first, leaving the more adaptable trees to continue living. He predicts that the trees in his German forest could even adapt to a southern European climate if they were left undisturbed and intact.
Chapter 31 Summary: “Turbulent Times”
In this chapter the author examines the natural disasters, or “turbulent times,” that trees must endure. He explains that while tornadoes and hurricanes are always a threat to a forest’s health, they can be especially damaging during the summer when trees are laden with leaves and therefore less resistant to high winds. These trees are left with devastating injuries such as broken crowns and exposed trunks. These powerful storms also stress trees by making them brunt the large impacts of rainfall or snowfall. Wohlleben reiterates that trees that are not straight and symmetrical are at high risk of succumbing to the pressure of these heavy impacts. Adult and adolescent trees are particularly at risk of acquiring too much snowfall on their branches, which causes them to break. Trees can also be significantly damaged by hoarfrost, lightning, and fire.
Some especially sensitive trees like the Douglas fir can be killed by lightning just by having their roots connected to another tree that is struck by it. In contrast other tree species, such as southern European cork oaks, have adapted fire-resistant bark that protects the buds underneath, allowing them to regrow once the fire has passed. Trees such as conifers, whose needles and bark are very flammable, did not evolve to be fire resistant because wildfires were extremely rare in northern forests. Wohlleben notes that even now, most forest fires are attributed to human activity. Ironically, when small fires cannot burn through forests regularly, the flammable twigs on the forest floor build up, making a massive forest fire more likely. He concludes his chapter by explaining that even changes in river height and temperature can affect tree growth: River flooding can suffocate tree roots, while winter ice floes can damage tree trunks with their impact.
Chapter 32 Summary: “Immigrants”
This chapter examines the relationship between trees and their native ecosystems. Many of the trees growing in Europe are native to North America, and vice versa. Because these “immigrant” trees are separated from the usual fungi, insects, and bacteria they would normally live with, they enjoy more freedom from pests in their first years apart from their native habitat. Wohlleben explains that Europe’s native beech trees tend to outcompete many non-native trees by shading them with their foliage, preventing their growth. However, when these ‘immigrant’ trees contain similar genetics to the native ones, they can hybridize and create a new line of trees with unpredictable traits. These hybrid trees are sometimes very successful and threaten to replace the native variety entirely.
Pests can also travel, often because of globalization. Wohlleben lists shipping containers and lumber as prominent sources of contamination that unintentionally transfer organisms from one continent to another. One example of these invasive species is the Asian long-horned beetle, which has successfully colonized many urban areas in Europe as a parasite on their trees. Wohlleben also reports that the parasitic ash dieback fungus has been aggressively killing ash trees in many European forests, but he adds that he is optimistic that resilient trees will overcome these challenges. Wohlleben then argues that if native ecosystems are “unspoiled” by people they are more likely to be able to withstand the challenges presented by invasive species (217).
Wohlleben includes an aside about the definitions of native and non-native. He argues that notions of native animals or plants should not be based on national borders but on habitats, which are “defined by their features (water, terrain, topography) and by the local climate” (219). This definition means that even bringing a spruce tree down a mountain and planting it in a nearby beech forest makes it a “nonnative” species in that specific habitat.
Chapters 29-32 Analysis
In these chapters, Wohlleben’s theme of human interference in natural systems becomes more pronounced, and he continues to offer his own commentary along with evidence to prove his points. His examples of human interactions with nature largely focus on the European context due to his own German background and expertise in Central European forestry. Wohlleben explains that there is a long history of human interference in nature in central Europe, citing pre-industrial logging, animal agriculture, and deforestation for crop growth as examples (191). He includes many examples of how human activity can inhibit forests’ ability to thrive. For example, he informs the reader that planted forests often grow in soil that has been compacted by heavy machinery. This leaves their root systems unable to expand healthily, resulting in weaker trees that are vulnerable to breaking in storms (201). He also points out that historically, forest fires have been quite rare in northern forests, and claims that most forest fires are caused by people behaving carelessly (207).
The author expands this theme by examining how global trade has hugely influenced the health of ecosystems around the world. Again, most of his examples include the European forests he is the most familiar with. He explains the complexities and risk of taking trees from one continent or ecosystem and growing them in another. In fact, he compares this to “a game of roulette” to illustrate how difficult it can be to predict the outcome for the tree of the forest as a whole (212). He provides the reader with the example of the black cherry tree, which was much loved in North America for its excellent lumber, but has become an invasive plant in Europe, where it thrives as a shorter, quick spreading tree.
He also explains how even microscopic pests can have a massive impact on ecosystems, calling them “foreign invaders” (218). He helps the reader understand how these pests can be transferred by explaining that bacteria, microorganisms, fungi, and even insects can reside in wood pallets, packages and wrapping that arrives from around the world. To illustrate this Wohlleben shares his experience of ordering an antique from North America and having to kill the small insects which had infiltrated his package. He shares another personal anecdote of visiting a forest which was afflicted with the invasive Asian fungus “ash dieback” and then noticing it had taken hold in his own forest shortly afterwards. When Wohlleben acknowledges that he may have been the one to accidentally spread this fungus by wearing the same shoes in each place, he acknowledges his own role as an actor in the ecosystem and also demonstrates how easy it is to make such a mistake (216).
Wohlleben believes that leaving forests undisturbed by human activity is the best strategy to help them combat invasive organisms and climate change. He also argues that some human intervention, while well-meaning, can hinder nature’s recovery. To illustrate his point, he shares an example of meadows in Germany which have been overrun with giant hogweed, an invasive plant from the Caucasus which can burn human skin. He questions why the government spends millions on digging up these plants when they always regrow vigorously. He argues that if authorities allowed the forest to regrow in these disturbed areas, the trees would eventually shade out the hogweed and kill them. Wohlleben emphasizes that people should work with natural systems to solve such problems, writing, “Trees could solve the problem if people trying to improve things would only allow them to take over” (218).
Wohlleben also uses these chapters to add more detail to his exploration of tree evolution and reproductive strategies. In addition to sharing more details about different tree seeds, he poses the question of why trees have evolved to travel and argues that this adaptation enables tree species to survive changing conditions, including climatic changes such as Ice Ages. He gives the example of our current climate, which has been warming since the last ice age, and increasingly so due to climate change. He writes that these changes have caused central European beech forests to slowly migrate northwards at a pace of a quarter mile per year.
Caucasus also explains more about trees’ ability to adapt to environmental changes. He compares trees to animals with short lifespans and efficient reproduction strategies, such as mice, to show how differently trees behave from animal species. Instead of quickly changing their genes, trees adapt using behavior and genetic variability. Here, multiple themes intersect, as Wohlleben urges the reader to support leaving old forests intact to give them the best chance of adapting to climate change and continuing to thrive. He argues that the warming climate is another reason to leave forests undisturbed so trees can remain healthy enough to appropriately change their behavior and reproduce young trees that will survive in our new climate era.
