Book Summary: The Hidden Life of Trees by Peter Wohlleben

Rating: 8.1/10.

The Hidden Life of Trees: What They Feel, How They Communicate – Discoveries from A Secret World by Peter Wohlleben

Book about forests and trees, made up of about 30 short chapters, it was originally written in German; each chapter describes some aspects of trees and it’s written in plain and non-technical language. The first few chapters tend to overly anthropomorphize and describe tree biological processes as though they are humans, which I generally disliked. However, after the first few chapters, it stopped doing this and became more scientific and objective.

Trees can help each other, much like a social network, by giving each other nutrients. This is beneficial because helping each other strengthens the group, which is good for all. They communicate amongst themselves through a tree’s roots and leaves, as well as with each other, using scents or chemicals. They respond to predators by releasing toxins which make their leaves bitter, but this happens relatively slowly.

When reproducing, trees have strategies to avoid inbreeding and will not fertilize themselves, which is crucial for genetic diversity and the future survival of the species. They release millions of seeds scattered in all directions, but statistically, only one is expected to survive to become a tree. One strategy they use is to wait a random number of years to grow, in case the conditions are unfavorable so that at least some will survive. The young seedling will wait for an opportunity to start growing, a chance occurs when more mature trees die and free up space in the canopy, allowing younger ones to have enough sunlight and take over.

Trees have straight trunks for stability, as anything else is less stable during a storm. The exception is if there is an open direction in one area, like a body of water, then it will bend over in that direction. Fungi sometimes feed on trees but can also be mutually beneficial – when they function as an extension of the root, they connect them to other trees and filter out toxins. Tree bark is a bit like skin: it keeps moisture in and dangers away from the outside. If it is broken, then fungi will come in and consume it, especially if it is dry, this is less of a risk if it is moist, since fungi cannot handle moisture.

In a forest, the beech tree is best at growing quickly in optimal and abundant conditions. It will take all of the available space, but other species are good at ecological niches. For example, spruce excels at cold winters, and yews, among others, are good at marginal conditions with little light. Small trees can survive in the Arctic and grow only to a small height over hundreds of years, can seem insignificant, but they can have long roots. Many small creatures live in the soil, often overlooked, and depend on specific conditions to thrive and may never recover if a forest is cut and then replanted.

Trees take carbon dioxide out of the atmosphere and turn it into biomass, which eventually, over millions of years, becomes coal. Interestingly, the oldest trees are the most efficient at this, making them an important factor in battling climate change. Beech trees angle their leaves to collect water during a storm and store it for later, but spruces don’t do this since they live in colder regions where groundwater is abundant. Forests act as water pumps for inland areas, allowing rain to fall by collecting moisture from trees and precipitating further inland. Without this process, rain would not penetrate more than 400 miles from an ocean.

There are lots of nutrients in trees that are protected by the bark. Many creatures try to access these nutrients by eating leaves or breaking through the bark, like woodpeckers and many others. Many species make their homes inside trees, like woodpeckers; other birds like owls prefer rotting trees, and their droppings provide nutrients for other organisms at the bottom of the trunk.

Trees shed leaves to be resistant to storms and to avoid being uprooted when there is a strong wind or a snowstorm, which can be heavy and crush branches if the leaves are not shed. They keep track of time based on factors such as temperature and day length, which is important for knowing when to grow and shed leaves. Trees that are planted indoors never get a chance to shed their leaves due to the absence of wind, and they die as this is a critical part of their life cycle.

Trees face decisions of risk-reward tradeoffs, such as whether to grow a new branch into a space that has recently become vacant. This can be risky because this space might be useless later or it might unbalance the tree. When a neighboring tree dies, it leaves spaces for the crown to grow, but this process takes a lot of energy to claim this spot quickly before another tree does. This is a risky strategy because it uses energy and the tree might not have enough energy to combat against fungal infections. Some trees, like birch, naturally live risky lives: they don’t try to live long but instead reproduce quickly and die quickly.

Trees are sometimes planted in urban environments, like beside city streets; urban trees tend to be weak because they are pruned and the roots don’t get enough room to grow as they are blocked by concrete, and might sometimes enter pipes for the moisture, which is undesirable for humans. Tree plantations also suffer from a lack of diversity: they differ from old-growth forests that have been cut; they are homogeneous and young, and since they lack diversity, they can die suddenly due to a beetle infestation.

Trees reproduce and expand their range when the seeds are carried by either wind or animals and land somewhere with favorable climatic conditions. They can change their behavior a little bit in response to environmental factors, but this is relatively limited. Most adaptation effectively happens using genetic diversity and natural selection to kill off the members of the species that are unsuitable to the environmental change. They are frequently harmed by environmental effects such as tornadoes, storms, fires, and flooding; usually they evolve some kind of mechanism to resist these events, but not in the case when they are relatively recent and caused by humans, in which case the trees are defenseless. Invasive species, when trees are transplanted to a different continent, may thrive or may die in an unexpected way as they are not adapted to the environment, this can cause a mess that is undesirable for humans, even though in the long term, it will adapt. The forest is green because it relies on chlorophyll for photosynthesis and green light cannot be used effectively, so it is reflected back as waste.

Overall, this book covers many different aspects of trees that are not very well known, especially since they share little with us making their behavior generally unintuitive. The only downside is I would’ve preferred some pictures to describe processes and to help the reader recognize them as they are happening in nature, otherwise it is difficult to identify things like what a fungus infection looks like.