The Hidden Life of Trees by Peter Wohlleben is one of the most interesting books I’ve read this year. I’ve written a summary and some of the more interesting points he makes here.
Peter Wohlleben sets out to describe the life of a tree and does so magnificently. He chronicles his own experiences as a forestry worker in Germany where he began with a view of trees as a resource and utility. Spending time in forests changed his perception and now drawing from his personal experience and the latest scientific research he works to change and reframe our perceptions of the individuals that are trees and forests in The Hidden Life of Trees.
The first chapter is aptly named “Friendships.” Here, Wohlleben tells the reader that beech trees feed one another. The story begins with a stump, apparently still alive! Wohlleben carved back the bark with a knife to reveal a green, living thing underneath the moss. Life required photosynthesis and sugar to feed the cells. How could a stump, he noted fell at least 400 years prior, still be alive? The answer is that trees feed and keep each other alive.
He refers to research done by scientists in the Harz mountains located in Germany that discovered that intertwined root systems really are cases of interdependence, and most individual trees of the same species growing in the same stand are connected to each other through their root systems. It appears that nutrient exchange and helping neighbors in times of need is the rule, and this leads to the conclusion that forests are superorganisms with interconnections much like ant colonies. Other studies have shown that plants, including trees are completely capable of distinguishing their own roots from the roots of other species and even from the roots of related individuals.
How do these trees communicate with each other? Through electrical impulses and through scent! Around 40 years ago scientists found something interesting while studying giraffes on the African savannah. They were eating the umbrella thorn acacias, something which the trees did not appreciate. Within a few minutes the acacia trees began secreting toxic substances to drive away the predators. After this occurred, the giraffes moved to different trees, not the other acacia trees nearby, but trees further away. Wohlleben writes that this was because the acacia trees released ethylene, a warning gas, to the neighboring trees. The message? There was a crisis! Right away, the other acacia trees began producing the same toxin and the giraffes seemed to know what was going on and moved farther away to unwitting trees. The scent messages are carried to the nearby trees using a breeze. So, if the giraffes moved upwind, the trees would have to repeat the process over again.
Similarly, when a caterpillar begins eating a leaf, the tissue surrounding the bite mark changes. Part of these changes sends out electrical signals to warn the rest of the plant, just as human tissue might do when it is injured. Unlike the rapid speed of our nervous system which transmits in milliseconds, plant signals travel at the measly pace of one-third an inch per minute. Likewise, trees can also warn each other using chemical signals which are sent through the fungal networks around their root tips (more on this later). This process knows no distance and can pass from tree to tree, leaving the trees a quick communication form with short range and a slow communication form with massive range. He notes though that it seems selective breeding has caused our cultivated plants to lose their ability to communicate. They do retain their visual abilities. Blossoms, in addition to their olfactory capabilities, are visually stimulating to insects in order to promote pollination. So far we’ve seen that trees are capable of communicating through sight, smell, and touch (electrical signals). Surprisingly, sound is included in this list.
Wohlleben refers to Monica Gagliano’s research in Australia where they listened to seedlings and were able to register roots crackling very quietly at a frequency of 220 hertz. By itself, this doesn’t mean much. What they found, however was that the roots of other seedlings began reacting. Whenever any roots were exposed to a crackling at that specific frequency, they would orient their tips towards the source of the sound, perhaps orienting themselves to the call of their neighbor. Roots also function through touch. It feels its way through the ground aware of the stimuli around it. If a root encounters hard ground or a rock it reorients the growing tip a different direction. Likewise, if it encounters a toxic substance it will turn around to avoid it. If it happens to come across rich soil, it will send more energy to develop that root system. It is the root of all chemical activity that occurs in the tree, functioning both as a sort of sensory organ and as a brain capable of responding to the stimuli.
The next chapter finds Wohlleben exploring photosynthesis in undisturbed beech forests. What he found was that the rate of photosynthesis was the same for all of the trees. It seems that they were synchronizing their activities so that they would all be equally successful. The trees were equalizing the differences between the strong ones and the weak ones. This transfer of resources takes place underground in the roots. When the trees are growing together they can divide up nutrients and water to those in need. If one tree falls behind due to illness or infestation, the other trees can provide support until it recovers, knowing that when it does recover it will do the same for them. Sometimes, when trees grow on their own, they will do better than others. These positive results are quite short-lived though. They lack the support system to be able to fight off infection, pests, or a decline in available nutrients. Likewise, if they lost the genetic lottery, they will be able to overcome it, whereas they might have survived longer with the help of neighbors. When people ask Wohlleben how long a tree will leave, he says that he tells them the metric is worthless when applied to an individual. The health of a tree depends on the stability of the forest ecosystem and on its relations to its neighbors. This is evident by some lightening strikes. Sometimes when lightening strikes it not only hurts the stricken tree but also those around it. Douglas Fir roots are quite sensitive. In multiple cases, not only did the tree struck by lightening die, but another dozen trees within 50 feet died as well. Likely they were connected by their root systems underground and were stuck sharing the same fate.
From Pollen to Sapling to Old Tree
Chapter four of The Hidden Life of Trees notes the slow, long-term planning and growth of trees in procreation as well. Wohlleben says reproduction is planned at least a year in advance by trees, whether this occurs every year depends on the species of tree. Conifers send their seeds out at least once a year. Deciduous trees follow a different timeline. Before blooming, they seem to decide whether they should produce for the next spring or if they should wait another year or more. They bloom at the same time so that the gene pool has a wide variety to select from. They also bloom at the same time in order to overwhelm the wild boars and deer so that at least some of their seedlings might survive to adulthood.
The base requirement before any seedlings can be sent out is pollination. Trees have to learn to pollinate each other without pollinating themselves. Solutions to this vary from tree to tree. One example Wohlleben notes is relying on timing. Male and female blossoms on spruce trees open a few days apart so that they won’t pollinate themselves. One of the few solutions relying on bees is produced by the bird cherry. They produce male and female sex organs on the same blossom. When pollen lands on the stigma, the genes are activated and it grows a tube down the ovary searching for an egg. During this process though, the tree is testing the genetic makeup of the pollen to make sure it is not its own. If it is then the tree blocks the tube to keep it from self-pollinating.
One key feature in reproducing is being able to maintain an inner balance, the subject of the next chapter. Wohlleben explains how trees budget their energy, making sure they have enough to meet all of the demands. They use this energy to grow by lengthening their branches and widening the diameter of the trunk to support the growth. Some of the energy is saved in case of an attack by insects or illness. The rest of the energy is put towards propagation. This poses a bit of a problem for species such as beeches or oaks that blossom every three to five years. Most of the energy is used for the typical tasks. The energy cost of producing beechnuts and acorns is so large that everything else gets put on the back burner. To make space for the blossoms many leaves drop off the branches. The tree then uses all of its energy to produce blossoms. This strains the tree greatly. Energy is depleted and there are fewer leaves to produce energy than normal. This is when pests strike. Healthy trees can usually overcome this because they have a few years to recover before the next bloom.
Wohllenben offers an idea of just how many seeds are produced. He says that every 5 years, a beech tree produces over thirty thousand beechnuts. The tree isn’t sexually mature until it is 80-150 years old. If the beech tree grows to be 400 years old then it will fruit around 60 times and produce 1.8 million beech nuts. Poplar trees produce 54 million seeds a year. Astonishingly, he says it is probably that only one mature tree will grow out of all of those seedlings. Trees can’t walk. But they need to be able to move in some way so that they are able to adapt to an environment. So they do so through the next generation. Some species seeds’, including ones like Poplars and willows, are almost as light as a feather so they can be blown about by the wind. They travel far, but can’t survive much. Other seeds are slightly heavier. Trees like ashes, birches, conifers, and maples equip their seeds with flying aids to make them able to travel farther. Species like beeches, chestnuts, or oaks’ seeds are too heavy and so rely on the animal kingdom to spread their posterity.
So what about the seeds that are dropped from these blossoms? Some species’ seeds sprout almost immediately in order to avoid danger. A lack of long-term defense is the trade-off for this. Other types of trees wait before growing. There is higher short-term danger (e.g. being eaten) but this allows for survival through drier seasons. Assuming they do survive, a beech sapling could grow up to 18 inches during each season. The mothers have a different idea in mind though. Only about 3% of light penetrates the canopies of their mothers. It is just enough for the sapling to keep itself from dying. What it does do is keep the tree from becoming too independent too quickly. Wohllenben presents research that determined that slow growth while a tree is young is a perquisite for a tree to be able to live to an old age. He suggests that we lose sight of that in modern forestry as they allow trees to get to 80-120 years before cutting them down–right as it is reaching adulthood.
This slow growth is essential. It causes the inner woody cells to be tiny and contain almost no air. This helps them to resist fungi and pests. This aids healing injuries too because the tree can easily close up any wounds before they start to decay. It also makes the trees flexible and more resistant to breaking during wind storms. The mothers pass the babies sugar and other nutrients to keep them alive. They take care of their young and are looking out for their best long-term health and wellness. As the young trees grow into “teenage” trees, their mothers begin to die. Once this happens, they are able to grow due to the increased sun seeping in through the open space in the canopy. This continues until the canopy is filled in by neighboring trees. Now they are medium-level trees in the pecking order. As the older neighbors die off they take their place at the top of the canopy becoming the elder trees.
Within these forests there is a proper way to do things. Wohlleben calls this forest etiquette. A mature, behaved deciduous tree has a straight trunk with roots stretching out evenly in all directions. As younger branches die off, the holes are sealed with bark and they become a smooth column up until the canopy. Here there is a symmetrical crown which is angled towards the sky. The goal of all of this is stability. The canopy is exposed to wind, rain, and snow leaving the rest of the tree to absorb the impact. Any weakness means the tree will break. Three types of trees that break this etiquette are described by Wohlleben. They are curved trunks, forked trees, and banana tree shapes. Curved trunks mean that the weight of the crown is unevenly divided. Only one side takes the brunt of the force and must be reinforced with thicker wood in order to keep it from crashing down. Forked trees apparently are even more problematic. Each fork of the tree has its own crown. This multiplies the force placed on the rest of the tree. The roots must be able to support twice (or more) the force of the wind on the tree. Additionally, one side of the tree might break. Water gathers at the site of the break and can lead to rot. According to Wohlleben, trees rarely survive more than a few decades after one of the forks breaks off. The final model is the banana tree. In these trees the lower part sticks out at an angle. At some point the tree grows upward again resulting in the banana shape. This can occur on hill sides or on the edge of forests where sunlight comes in from the side.
Image by Mabel Amber from Pixabay
The Learning Capabilities of Trees
In the next chapter Wohllenben address the learning capabilities of trees. Trees can adapt to hunger more easily than thirst. Mature beech trees move 130 gallons of water a day within themselves. If they pulled this from the soil every day during the drier summers, there would be no water left. To counteract this the trees store water in the winter when they aren’t using much. But, if the ground dries up for too long and the tree begins to run out of stores, the drying of the wood can cause tears in the bark. These tears cause major injuries to the tree, especially from fungal spores that take advantage of this tear. The trees will repair the wound as best they can but it will continue to reopen as the fungi work their destruction. What it does learn from these situations is to ration its water more efficiently. Instead of taking whatever is left in the ground it will continue to ration it even as water returns.
Another thing that trees learn how to do is to support themselves for the most part. Often you will find trees leaning on each other, supporting each other’s weight reducing the need for a sturdy trunk. Trees also support each other during wind storms. The crowns will often times bump into each other and slow each other’s rebound. This is problematic when their neighbors die off or get cut down. For the next few years, and even for the next decade (trees are slow growers), they are vulnerable. Their root systems have to learn and grow to support them. It is a process to learn how to be stable. It gets activated by the micro-tears that happen when the wind blows the trees in many directions. Wherever it gets bent the tree works to strengthen. Strengthening themselves takes energy, energy that could be spent growing upwards. Each time a gap is opened as another tree dies, this process occurs over again.
Wohlleben then presents Monica Gagliano’s work on plant-learning. She studies mimosas, which are tropical creeping herbs. When touched, these plants close their leaves to protect themselves. Gagliano ran an experiment where she had a single drop of water fall onto the leaves at regular intervals. The plants first reacted to these droplets by closing their leaves quickly. As time passed the plants learned that the water didn’t present any danger and so the plants began leaving their leaves open while the drops continued. These plants remembered this weeks later when we restarted the tests on them again.
Another form of learning takes place from their neighbors according to Wohlleben. He presents research that recorded sounds at ultrasonic levels. When trees get really thirsty they start to scream. They found that vibrations begin when the flow of water between the roots and leaves is disrupted. This might just be a mechanical event, he says, but suggests that just as our vocal chords vibrate when we talk, the trees might be saying more: warning their neighbors of the low water levels. This talk leads to his next chapter “United We Stand, Divided We Fall” where Wohlleben continues to show trees are social beings, not just with each other, but with fungi as well.
Trees and Their Associates
Trees and fungi have been partnering for millions of years. Fungi, Wohlleben says, are in between animals and plants. They are more like insects than plants because their cell walls are made of chitin, something not found in plants. Fungi also do not photosynthesize. They depend on connections with other living things to feed them. Fungi allow the tree to increase its root surface enabling it to absorb more water and nutrients. He shows that you can find twice the nitrogen and phosphorus (essential components of life) in plants that work with fungi than in those who do not work with fungi. The fungi’s system also grows wider than the trees roots enabling the tree to reach further than it could have on its own. It is in this extension that trees and other fungi connect to each other creating a network that Wohlleben compares to the internet. The tree provides food for the fungi while the fungi filter out heavy metals which are detrimental to the tree’s growth. Some fungi are picky and “host specific” and only pair with a certain kind of tree. Another service fungi provide is as a negotiator. These fungal networks promote compromise among differing tree species. They also serve as an elite task force for when environmental situations are bad. One example Wohlleben provides is of the pine tree and its ally, the Laccaria bicolor. When there isn’t enough nitrogen the fungus releases a toxin into the soil killing off smaller organisms like the springtail. This releases the nitrogen they have stored providing fertilizer for the tree and fungi.
From this point The Hidden Life of Trees moves on to how water moves from the soil to the trees. Wohlleben presents the traditional answers of capillary action and transpiration. The former is what allows water to rise above the edge of a cup. The narrower the container the higher the liquid can rise. The latter is the evaporation of water. In cases of mature beech trees, he says, they can exhale or evaporate hundreds of gallons of water each day and this exhalation causes suction. The suction pulls water up through the tree and circulates it. One interesting anecdote is that the water pressure in trees is highest just before the leaves open in spring. This is why syrup is harvested from sugar maples at this time of year.
Trees also serve as water pumps for the local and non-local ecosystems. Trees have the largest surface covered in leaves of any plant. Every square yard of forest yields 27 square yards of leaves and needles in the crowns of the trees. These leaves catch part of every rainfall and allow it to evaporate as soon as the rain ends. Each summer trees use 8500 cubic yards of water per square mile. This water is released back into the air through transpiration. This water vapor is what creates new clouds that can travel and provide water elsewhere as the clouds move. Coastal forests provide a foundation for moving water inland. As clouds form over the ocean and bring rain to the coast, the forests absorb it and then release it again, this time closer to the inland. These clouds move farther inland and provide water to other regions. If forests near the coasts don’t exist the water cannot travel inland as they provide the foundation for the system. Forests are the water pumps of the world.
Trees, Their Environment and Healthy Aging
The next section of the book approaches the aging of trees and their environment. Bark is similar to skin. They serve the same function–protecting the inner organs from the outside world. Bark also keeps a tree from drying out. Fungi begin to break down dry wood and insects need drier wood to breathe. If there is too much moisture in the wood they will suffocate. Wohlleben compares a break in tree bark to a wound on our skin. He suggests they are just as uncomfortable and rely on the same mechanisms as skin to keep this from occurring. Bark replaces itself just as skin does. Beeches bark is smooth until they reach nearly two-hundred years old because the rate of renewal is high. This allows the skin to remain thin and continue to fit and doesn’t need to crack in order to expand like pine bark does. Pine bark is extremely thick. This means the exterior layers can sometimes be more than a decade old. A rule of thumb is the deeper the cracks are in the bark the more hesitant the tree sheds its bark.
Image by Karsten Paulick from Pixabay 
Image by Надежда Зима from Pixabay
Just as human skin varies in how much it wrinkles, so to does bark. Likewise, more light, sun, and UV radiation causes more wrinkles in bark as it does with human skin. The bark on the sunny side of the tree is harder, less flexible, and more likely to crack. When trees are sick sometimes these cracks develop wounds. If they stay moist then bacteria move in and “infect” the wound. This happens more often on older trees. Old trees also have time to gather moss on their branches over time. The algae that grows on this moss actually gathers nitrogen from the air and turns it into a form the trees can utilize. When it rains, this fertilizer runs down the tree and can be used by its roots. Speaking of older trees, Wohlleben dispels the myth that young trees grow the fastest. The older the tree the more quickly it grows. It doesn’t mean being weak, bowed, and fragile. It means being full of energy and highly productive.
Wohlleben uses oak trees as an example of the role an environment can play in shaping the course of a tree’s life. In the beech-dominated forest he manages, oaks are often in distress. The little sprouts at the bottom of the trunk make this apparent. These little sprouts don’t receive any light and die off. These oaks struggle because beeches are only social trees within their species. They try to choke out the oaks. While beeches may dominate in their social groups, oaks can withstand climates that would kill the beech trees off. Along the sides of mountains and cliffs oaks thrive because the beeches cannot survive. Despite being smaller than oaks growing in ideal conditions, these oaks live well due to the lack of competition. This example is meant to show in part that trees make do in extreme environments. The tree’s dream of nutrient-rich and loose soil doesn’t exist in many places around the world. They must make do with what they can. Another example Wohlleben provides is the spruce tree. They survive everywhere where summers are short and winters are freezing cold. They can survive this because they store oils in their needles and bark that serve as anti-freeze. This, as you might remember, can pose a problem. Snow gathers on the needles and can weigh the tree down. To combat this spruce trees grow completely straight trunks to keep an equal weight distribution. The branches also angle downward once snow builds up layering on each other to provide a support system.
As well as trees can adapt, they don’t like extreme changes in their environment. Changes in temperature or moisture are especially hard on trees. They can change their environment, albeit slowly. One example The Hidden Life of Trees provides is a forest in Germany that was said to only be able to grow pine trees. In an attempt to diversify the forest, forestry workers added beech trees to try to neutralize the acid produced by the pine needles. In just a few decades the beeches created a more alkaline humus on the ground in order to store water. The leaves of the beeches reduced the speed of the wind that was flowing through the pine trees. Slower air movement meant less water evaporating and moister air. The beeches began to prosper and beat out the pine trees.
The “Hidden Life of Trees” is also the hidden life of an ecosystem. Half of the biomass of a forest is found in the soil. Central to the health of the soil are thousands of different creatures including mites, weevils, beetles, etc. These creatures are central to maintaining the health of the soil. Wohlleben points to research showing that the return of these creatures takes quite a long time. Oak forests were planted in an area of Germany that used to be arable land. Even after one-hundred years there are still hundreds of missing species. This affects the proper function of the nutrient cycles of birth and decay. Dead wood is indispensable for the forest. The creatures in the soil break down the nutrients and make them available to other plants. Some of these creatures provide food for other birds and animals. Many insects feed on the sap of trees. One line of defense for the trees are birds. Woodpeckers eat this insects, but also peck their way into the tree to make a home. Slowly bacteria and water make the exposed wood mushy. This causes the woodpeckers to expand their home further. Eventually it becomes too big for them to raise babies in. At this point other birds move in and over time, as the hole rots bigger and bigger, owls and bats begin to make their homes in these cavities and will stay even after a tree has died. Wohlleben remarks that over a fifth of all the animal and plant species depend on dead wood.
The hidden life of trees also includes an inner grizzly bear. Just like bears, trees require hibernation. This means storing up food for the winter. This takes a lot of time and resources. They can’t switch into winter mode too early. The trees need to fetch the energy reserves from the leaves and bring them back to the trunk and roots. They also need to break down the chlorophyll that is in the leaves so that they can send it back out in the spring to the new leaves. The pigment is pumped out of the leaves which turns them yellow and brown. The colors also serve as a defense signal against aphids and other insects who are seeking shelter from the winter in the cracks in the bark. Healthy trees show their defenses with their colored leaves in the fall. Aphids recognize these as well-defended and move to the weaker and less colorful trees. After the nutrients have been recalled from the leaves the trees grow a layer of cells to close off the connection between the leaves and branches. This is what makes it so easy for the leaves to fall off in the wind. Once this process is complete the tree can finally rest. This rest is essential. Just as humans need sleep so do trees. Young trees, however, are usually the last ones to lose their lives. This is so they can soak up as much sun as they can. Likewise they are the first to produce leaves in the spring, partially because the ground is warmer than the top of the trees signaling the time to grow new leaves. Many flowers and shrubs in deciduous forests bloom early because that is when there is available light. All their work has to be done in a month or two before the canopy closes back up with the tree’s leaves.
In order to hibernate, trees must have a sense of time. It makes sense that warm days trigger leaf growth. The warmth melts the frozen water in the tree trunk and allows it to flow again. What is unusual, points out Wohlleben is that the colder the preceding winter, the earlier the leaves come back and the warmer the cold season, the later some trees (like beeches) will green up. Trees require a certain number of warm days before greening up. They also wait until there is a certain amount of light each day. He suggests that this proves that trees must have a memory. How else could they inwardly compare day lengths or count warm days? For example, beeches require at least 13 hours of daylight before they will grow leaves. In warmer years when there are high autumn temperatures, some trees’ sense of time gets confused. You will see their buds grow in December with some trees even putting out new leaves. When this happens the trees are in trouble. The new growth doesn’t have time to get hard and woody for winter and the leaves are defenseless. So when the frost comes, it all dies off. The new buds are lost and replacements must be grown for next spring (assuming the tree has energy for them). One interesting fact he provides is that trees will adapt if they are sent to the opposite hemisphere. They will switch from what they are used to in order to survive
One aspect of the hidden life of trees Wohlleben wants to suggest is that trees have character or personality. For example, on a road near him are three oak trees. The one-hundred-year-old trunks are just a few inches apart. The environmental conditions can’t differ much between them. So if oaks behave differently, it must be because of their own innate characteristics. He observed that in the falls the oak on the right already began turning colors while the other two were still completely green. It took a few weeks for the other two to turn colors. But the growing conditions were identical, so what accounts for the differences in behavior other than innate character? He suggests the one on the right might be more anxious or maybe more sensible. What good are the extra stores if you can’t shed your leaves? Perhaps we should ask those oak trees! He does say that mature trees can adapt. It a spruce survives a dry period, later they become more economical with the water. It also might put out a thicker coat on the leaves to reduce transpiration. Once it has exhausted the variety of behavioral options it has, genetics come into play. The genetic makeup of trees belonging to the same species is very different. While humans are very similar genetically, individual trees are genetically as far apart as different species of animals. This means each tree can have vastly different characteristics. This might be an explanation for the oak trees differences.
The Urban Life of Trees
In the next chapter Wohlleben addresses the trees in an urban context. He asks why the giant redwood trees in Europe aren’t as tall as one would expect. He suggests it is partially due to their location, alone along streets. There are no relatives there to care for it or to provide assistance or protection as there would be in a forest. Likewise, the soil is probably sub-optimal. And whereas the old-growth forest offers soft, crumbly, humus-rich, and constantly moist soil for their delicate roots, European parks offer hard surfaces that have been depleted of nutrients and compacted after years of urbanization. People trample the base of the tree further compacting the soil making the rain drain away too quickly.
He suggests that the mechanics of planting hurt the trees for the rest of their lives. Every fall their roots are trimmed to keep them compact so they can be moved more easily. the root ball, which would grow to about 20 feet in diameter for a 10-foot-tall tree is cut back to about 20 inches. This interference also makes the trees lose their sense of direction underground. They stop growing roots down and instead grow near the surface. Above ground pruning done at parks restricts the amount of photosynthesis that can occur, which is a substantial blow for the roots whose size is carefully optimized to serve the top of the tree.
There are some cases of trees growing into pipes in the urban realm. It was initially thought that the trees were after nutrients leaking from the pipes. But after research was done, it was found that the tree roots were seeking out the least-compacted soil (as the soil under sidewalks and roads is extremely compacted) and only incidentally penetrated the seals of pipes. Once the replacement was made the ground was packed down more tightly and tree roots stopped growing in that direction.
This is not all the trees have to bear though. The urban climate is hotter due to the asphalt and concrete that is everywhere. Forests cool themselves at night while cities stay warmer. The warmer air leads to drier air that is full of exhaust fumes. This keeps many of the microorganisms that look after the trees away. They also have to deal with unsolicited fertilizers and dog urine (which can burn bark and roots) as well as salt on the roadways. The salt gets kicked up by cars and lands on tree foliage, burning it and reducing the rate of photosynthesis. This weakens the tree leaving them vulnerable to disease and pests.
When it comes to the urban climate, people think of trees and other plants as providing fresh air. Wohlleben shows that trees catch and filter out particles in the air. They also add substances to the air in order to talk to each other. He suggests that threatened, non-native, forests are inherently unstable and would have negative signals. Wohlleben says that walkers who visit the ancient deciduous preserves in the forests he manages report that their heart feels lighter and that they feel right at home. But if they walk through coniferous forests, which in Central Europe are mostly planted and are more fragile, artificial places, they don’t experience the same feelings. This could be because in ancient beech forests, fewer “alarm calls” go out, and most messages exchanged between trees are contended ones and said messages reach our brains as well, via our noses. A study was done in Korea on older women walking through forests and urban areas. When the women were walking in the forest their blood pressure, lung capacity, and the elasticity of their arteries improved. None of which were improved while walking in urban areas. One myth he dispels is that the forest air is rich in oxygen. During summer trees release around 29 tons of oxygen per square mile of forest. That is only during the day though. At night trees are busy using carbohydrates and releasing carbon dioxide, they are “sleeping”. Sleep is just as necessary for a tree as it is for a human.
Trees also function as carbon dioxide vacuums. While trees are photosynthesizing they are producing hydrocarbons. These fuel their growth. Over the course of a tree’s life it will store 22 tons of carbon dioxide in their trunks, branches, and roots. When they die however, the exact same quantity of carbon dioxide is released while the fungi and bacteria break down the wood. But, as the trees sink deeper into the earth while being decomposed, the process slows down. This means that not all of the carbon dioxide is released into the air–it gets stored in the ground. But, when we dig it up (sometimes in the form of fossil fuels) all of that carbon dioxide that was trapped gets released.
The final chapters of The Hidden Life of Trees are Wohlleben making sense of balancing forest growth with human consumption of lumber. Wohlleben takes care to say he isn’t condemning our usage of trees, as we are a part of nature just as plants and animals are. The real question he poses is whether we help ourselves to what we need and whether we spare the trees from unnecessary suffering when we do this. He suggests that trees should be allowed to live in a way that is appropriate to their species–able to fulfill their social needs and grow on undisturbed ground. He says that at least some of them should be allowed to grow old with dignity and die a natural death. Wohlleben argues that when the capabilities of even vegetative beings become known and their emotional lives and needs are recognized then the way we treat plants will gradually change. Forests should not be lumber suppliers and then only secondarily be habitats for thousands of species. It should be the exact opposite. Trees and forests should be seen as living things and habitats for thousands of species.
Pingback: Gluons and the Interconnectedness of Things - Alex Criddle