Highlights from The Hidden Life of Trees: What They Feel, How They Communicate—Discoveries from a Secret World, by Peter Wohlleben, Tim Flannery, and Jane Billinghurst

Sent by Fran, this Good Friday… the posted highlights beneath are inspired by her and all her good work in Massachusetts!

“i thank You God for most this amazing” by e.e. cummings

i thank You God for most this amazing
day:for the leaping greenly spirits of trees
and a blue true dream of sky; and for everything
which is natural which is infinite which is yes

(i who have died am alive again today,
and this is the sun’s birthday; this is the birth
day of life and of love and wings: and of the gay
great happening illimitably earth)

how should tasting touching hearing seeing
breathing any–lifted from the no
of all nothing–human merely being
doubt unimaginable You?

(now the ears of my ears awake and
now the eyes of my eyes are opened)

e.e. cummings

The Hidden Life of Trees: What They Feel, How They Communicate—Discoveries from a Secret World, by Peter Wohlleben, Tim Flannery, and Jane Billinghurst

Location references are to the kindle version.

Location: 38 One reason that many of us fail to understand trees is that they live on a different time scale than us. One of the oldest trees on Earth, a spruce in Sweden, is more than 9,500 years old. That’s 115 times longer than the average human lifetime. Creatures with such a luxury of time on their hands can afford to take things at a leisurely pace. The electrical impulses that pass through the roots of trees, for example, move at the slow rate of one third of an inch per second.

Location: 41 Why, you might ask, do trees pass electrical impulses through their tissues at all? The answer is that trees need to communicate, and electrical impulses are just one of their many means of communication. Trees also use the senses of smell and taste for communication. If a giraffe starts eating an African acacia, the tree releases a chemical into the air that signals that a threat is at hand. As the chemical drifts through the air and reaches other trees, they “smell” it and are warned of the danger. Even before the giraffe reaches them, they begin producing toxic chemicals. Insect pests are dealt with slightly differently. The saliva of leaf-eating insects can be “tasted” by the leaf being eaten. In response, the tree sends out a chemical signal that attracts predators that feed on that particular leaf-eating insect.

Location: 47 The most astonishing thing about trees is how social they are. The trees in a forest care for each other, sometimes even going so far as to nourish the stump of a felled tree for centuries after it was cut down by feeding it sugars and other nutrients, and so keeping it alive. Only some stumps are thus nourished. Perhaps they are the parents of the trees that make up the forest of today. A tree’s most important means of staying connected to other trees is a “wood wide web” of soil fungi that connects vegetation in an intimate network that allows the sharing of an enormous amount of information and goods. Scientific research aimed at understanding the astonishing abilities of this partnership between fungi and plant has only just begun.

Location: 53 It takes a forest to create a microclimate suitable for tree growth and sustenance. So it’s not surprising that isolated trees have far shorter lives than those living connected together in forests. Perhaps the saddest plants of all are those we have enslaved in our agricultural systems. They seem to have lost the ability to communicate, and, as Wohlleben says, are thus rendered deaf and dumb.

Location: 67 This book is a lens to help you take a closer look at what you might have taken for granted. Slow down, breathe deep, and look around. What can you hear? What do you see? How do you feel? My story also explains why forests matter on a global scale. Trees are important, but when trees unite to create a fully functioning forest, you really can say that the whole is greater than its parts. Your trees may not function exactly as my trees do, and your forest might look a little different, but the underlying narrative is the same: forests matter at a more fundamental level than most of us realize.

Location: 99 When you know that trees experience pain and have memories and that tree parents live together with their children, then you can no longer just chop them down and disrupt their lives with large machines. Machines have been banned from the forest (here) for a couple of decades now, and if a few individual trees need to be harvested from time to time, the work is done with care by foresters using horses instead. A healthier—perhaps you could even say happier—forest is considerably more productive, and that means it is also more profitable.

Location: 123 No being on our planet can maintain a centuries-long fast, not even the remains of a tree, and certainly not a stump that has had to survive on its own. It was clear that something else was happening with this stump. It must be getting assistance from neighboring trees, specifically from their roots. Scientists investigating similar situations have discovered that assistance may either be delivered remotely by fungal networks around the root tips—which facilitate nutrient exchange between trees1—or the roots themselves may be interconnected.2 In the case of the stump I had stumbled upon, I couldn’t find out what was going on, because I didn’t want to injure the old stump by digging around it, but one thing was clear: the surrounding beeches were pumping sugar to the stump to keep it alive.

Location: 132 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.

Location: 138 According to Massimo Maffei from the University of Turin, plants—and that includes trees—are perfectly capable of distinguishing their own roots from the roots of other species and even from the roots of related individuals.3 But why are trees such social beings? Why do they share food with their own species and sometimes even go so far as to nourish their competitors? The reasons are the same as for human communities: there are advantages to working together.

Location: 142 A tree is not a forest. On its own, a tree cannot establish a consistent local climate. It is at the mercy of wind and weather. But together, many trees create an ecosystem that moderates extremes of heat and cold, stores a great deal of water, and generates a great deal of humidity. And in this protected environment, trees can live to be very old. To get to this point, the community must remain intact no matter what.

Location: 144 If every tree were looking out only for itself, then quite a few of them would never reach old age. Regular fatalities would result in many large gaps in the tree canopy, which would make it easier for storms to get inside the forest and uproot more trees. The heat of summer would reach the forest floor and dry it out. Every tree would suffer.  Every tree, therefore, is valuable to the community and worth keeping around for as long as possible. And that is why even sick individuals are supported and nourished until they recover.

Location: 147 Every tree, therefore, is valuable to the community and worth keeping around for as long as possible. And that is why even sick individuals are supported and nourished until they recover. Next time, perhaps it will be the other way around, and the supporting tree might be the one in need of assistance. When thick silver-gray beeches behave like this, they remind me of a herd of elephants. Like the herd, they, too, look after their own, and they help their sick and weak back up onto their feet. They are even reluctant to abandon their dead.

Location: 149 Every tree is a member of this community, but there are different levels of membership. For example, most stumps rot away into humus and disappear within a couple of hundred years (which is not very long for a tree). Only a few individuals are kept alive over the centuries, like the mossy “stones” I’ve just described.

Location: 161 As a rule, friendships that extend to looking after stumps can only be established in undisturbed forests. It could well be that all trees do this and not just beeches. I myself have observed oak, fir, spruce, and Douglas fir stumps that were still alive long after the trees had been cut down. Planted forests, which is what most of the coniferous forests in Central Europe are, behave more like the street kids I describe in chapter 27. Because their roots are irreparably damaged when they are planted, they seem almost incapable of networking with one another. As a rule, trees in planted forests like these behave like loners and suffer from their isolation. Most of them never have the opportunity to grow old anyway. Depending on the species, these trees are considered ready to harvest when they are only about a hundred years old.

Location: 172 Trees, it turns out, have a completely different way of communicating: they use scent. Scent as a means of communication? The concept is not totally unfamiliar to us. Why else would we use deodorants and perfumes? And even when we’re not using these products, our own smell says something to other people, both consciously and subconsciously. There are some people who seem to have no smell at all; we are strongly attracted to others because of their aroma. Scientists believe pheromones in sweat are a decisive factor when we choose our partners—in

Location: 176 It seems fair to say that we possess a secret language of scent, and trees have demonstrated that they do as well. For example, four decades ago, scientists noticed something on the African savannah. The giraffes there were feeding on umbrella thorn acacias, and the trees didn’t like this one bit. It took the acacias mere minutes to start pumping toxic substances into their leaves to rid themselves of the large herbivores. The giraffes got the message and moved on to other trees in the vicinity. But did they move on to trees close by? No, for the time being, they walked right by a few trees and resumed their meal only when they had moved about 100 yards away.

Location: 181 The reason for this behavior is astonishing. The acacia trees that were being eaten gave off a warning gas (specifically, ethylene) that signaled to neighboring trees of the same species that a crisis was at hand. Right away, all the forewarned trees also pumped toxins into their leaves to prepare themselves. The giraffes were wise to this game and therefore moved farther away to a part of the savannah where they could find trees that were oblivious to what was going on. Or else they moved upwind. For the scent messages are carried to… Some highlights have been hidden or truncated due to export limits.

Location: 186 Beeches, spruce, and oaks all register pain as soon as some creature starts nibbling on them. When a caterpillar takes a hearty bite out of a leaf, the tissue around the site of the damage changes. In addition, the leaf tissue sends out electrical signals, just as human tissue does when it is hurt. However, the signal is not transmitted in milliseconds, as human signals are; instead, the plant signal travels at the slow speed of a third of an inch per second… Some highlights have been hidden or truncated due to export limits.

Location: 192 These are not just any old scent compounds, but compounds that are specifically formulated for the task at hand. This ability to produce different compounds is another feature that helps trees fend off attack for a while. When it comes to some species of insects, trees can accurately identify which bad guys they are up against. The saliva of each species is different, and trees can match the saliva to the insect. Indeed, the match can be so precise that trees can release pheromones that summon specific beneficial predators. The beneficial predators help trees by eagerly devouring the insects that are bothering them. For example, elms and pines call on small… Some highlights have been hidden or truncated due to export limits.

Location: 198 The result, however, is that the trees are saved from bothersome pests and can keep growing with no further damage. The fact trees can recognize saliva is, incidentally, evidence for yet another skill they must have. For if they can identify saliva, they must also have a sense of taste. A drawback of scent compounds is that they disperse quickly in the air. Often they can be detected only within a range of about 100 yards. Quick dispersal, however, also has advantages. As the transmission of signals inside the tree is very slow, a… Some highlights have been hidden or truncated due to export limits.

Location: 203 A specialized distress call is not always necessary when a tree needs to mount a defense against insects. The animal world simply registers the tree’s basic chemical alarm call. It then knows some kind of attack is taking place and predatory species should mobilize. Whoever is… Some highlights have been hidden or truncated due to export limits.

Location: 235 When we step into farm fields, the vegetation becomes very quiet. Thanks to selective breeding, our cultivated plants have, for the most part, lost their ability to communicate above or below ground—you could say they are deaf and dumb—and therefore they are easy prey for insect pests.12 That is one reason why modern agriculture uses so many pesticides.

Location: 245 So trees communicate by means of olfactory, visual, and electrical signals. (The electrical signals travel via a form of nerve cell at the tips of the roots.)

Location: 247 Along with colleagues from Bristol and Florence, Dr. Monica Gagliano from the University of Western Australia has, quite literally, had her ear to the ground.13 It’s not practical to study trees in the laboratory; therefore, researchers substitute grain seedlings because they are easier to handle. They started listening, and it didn’t take them long to discover that their measuring apparatus was registering roots crackling quietly at a frequency of 220 hertz.

Location: 252 The roots of seedlings not directly involved in the experiment reacted. Whenever the seedlings’ roots were exposed to a crackling at 220 hertz, they oriented their tips in that direction. That means the grasses were registering this frequency, so it makes sense to say they “heard” it. Plants communicating by means of sound waves? That makes me curious to know more, because people also communicate using sound waves. Might this be a key to getting to know trees better? To say nothing of what it would mean if we could hear whether all was well with beeches, oaks, and pines, or whether something was up. Unfortunately, we are not that far advanced, and research in this field is just beginning.

Location: 270 Beeches, at least, seem to set a great deal of store by sharing resources. Students at the Institute for Environmental Research at RWTH Aachen discovered something amazing about photosynthesis in undisturbed beech forests. Apparently, the trees synchronize their performance so that they are all equally successful. And that is not what one would expect. Each beech tree grows in a unique location, and conditions can vary greatly in just a few yards. The soil can be stony or loose. It can retain a great deal of water or almost no water. It can be full of nutrients or extremely barren.

Location: 274 Accordingly, each tree experiences different growing conditions; therefore, each tree grows more quickly or more slowly and produces more or less sugar or wood, and thus you would expect every tree to be photosynthesizing at a different rate. And that’s what makes the research results so astounding. The rate of photosynthesis is the same for all the trees. The trees, it seems, are equalizing differences between the strong and the weak. Whether they are thick or thin, all members of the same species are using light to produce the same amount of sugar per leaf. This equalization is taking place underground through the roots.

Location: 279 There’s obviously a lively exchange going on down there. Whoever has an abundance of sugar hands some over; whoever is running short gets help. Once again, fungi are involved. Their enormous networks act as gigantic redistribution mechanisms. It’s a bit like the way social security systems operate to ensure individual members of society don’t fall too far behind.14 In such a system, it is not possible for the trees to grow too close to each other. Quite the opposite. Huddling together (the trees share more).

Location: 284 Colleagues from Lübeck in northern Germany have discovered that a beech forest is more productive when the trees are packed together. A clear annual increase in biomass, above all wood production.

Location: 287 Water can be optimally divided among them all so that each tree can grow into the best tree it can be. If you “help” individual trees by getting rid of their supposed competition, the remaining trees are bereft. They send messages out to their neighbors in vain, because nothing remains but stumps. Every tree now muddles along on its own, giving rise to great differences in productivity. Some individuals photosynthesize like mad until sugar… Some highlights have been hidden or truncated due to export limits.

Location: 291 This is because a tree can be only as strong as the forest that surrounds it. And there are now a lot of losers in the forest. Weaker members, who would once have been supported by the stronger ones, suddenly fall behind. Whether the reason for their decline is their location and lack of nutrients, a… Some highlights have been hidden or truncated due to export limits.

Location: 294 Their well-being depends on their community, and when the supposedly feeble trees disappear, the others lose as well. When that happens, the forest is no longer a single closed unit. Hot sun and swirling winds can now penetrate to the forest floor and disrupt the moist, cool climate. Even strong trees get sick a lot over the course of their lives. When this happens, they depend on their weaker neighbors for support. If they are no longer… Some highlights have been hidden or truncated due to export limits.

Location: 309 I have learned from this just how powerful a community of trees can be. “A chain is only as strong as its weakest link.” Trees could have come up with this old craftsperson’s saying. And because they know this intuitively, they do not hesitate to help each other out.

Location: 313 Reproduction is planned at least a year in advance. Whether tree love happens every spring depends on the species. Whereas conifers send their seeds out into the world at least once a year, deciduous trees have a completely different strategy. Before they bloom, they agree among themselves. Should they go for it next spring, or would it be better to wait a year or two? Trees in a forest prefer to bloom at the same time so that the genes of many individual trees can be well mixed. Conifers and deciduous trees agree on this, but deciduous trees have one other factor to consider: browsers such as wild boar and deer.

Location: 345 Trees have survived until today only because there is a great deal of genetic diversity within each species. If they all release their pollen at the same time, then the tiny grains of pollen from all the trees mix together and drift through the canopy. And because a tree’s own pollen is particularly concentrated around its own branches, there’s a real danger its pollen will end up fertilizing its own female flowers. But, as I just mentioned, that is precisely what the trees want to avoid. To reduce this possibility, trees have come up with a number of different strategies.

Location: 349 Some species—like spruce—rely on timing. Male and female blossoms open a few days apart so that, most of the time, the latter will be dusted with the foreign pollen of other spruce. This is not an option for trees like bird cherries, which rely on insects. Bird cherries produce male and female sex organs in the same blossom, and they are one of the few species of true forest trees that allow themselves to be pollinated by bees.

Location: 353 The bird cherry is alert and senses when the danger of inbreeding looms. When a pollen grain lands on a stigma, its genes are activated and it grows a delicate tube down to the ovary in search of an egg. As it is doing this, the tree tests the genetic makeup of the pollen and, if it matches its own, blocks the tube, which then dries up. Only foreign genes, that is to say, genes that promise future success, are allowed entry to form seeds and fruit. How does the bird cherry distinguish between “mine” and “yours”? We don’t know exactly. What we do know is that the genes must be activated, and they must pass the tree’s test. You could say, the tree can “feel” them.

Location: 363 Willows, like bird cherries, also rely on insects for pollination. But here a problem arises. The bees must first fly to the male willows, collect pollen there, and then transport the pollen to the female trees. If it was the other way around, there would be no fertilization. How does a tree manage this if both sexes have to bloom at the same time? Scientists have discovered that all willows secrete an alluring scent to attract bees. Once the insects arrive in the target area, the willows switch to visual signals. With this in mind, male willows put a lot of effort into their catkins and make them bright yellow. This attracts the bees to them first. Once the bees have had their first meal of sugary nectar, they leave and visit the inconspicuous

Location: 374 TREES MAINTAIN AN inner balance. They budget their strength carefully, and they must be economical with energy so that they can meet all their needs. They expend some energy growing. They must lengthen their branches and widen the diameter of their trunks to support their increasing weight. They also hold some energy in reserve so that they can react immediately and activate defensive compounds in their leaves and bark if insects or fungi attack. Finally, there is the question of propagation.

Location: 394 We know from times of high forest mortality that it is usually the particularly battered individuals that burst into bloom. If they die, their genetic legacy might disappear, and so they probably want to reproduce right away to make sure it continues. Something similar happens after unusually hot summers. After extreme droughts bring many trees to the brink of death, they all bloom together the following year, which goes to show that large quantities of beechnuts and acorns don’t indicate that the next winter will be particularly harsh. As blossoms are set the summer before, the abundance of fruit reflects what happened the previous year and has nothing to do with what will happen in the future.

Location: 411 Bird cherries adopt this strategy: their seeds can lie dormant for up to five years, waiting for the right time to sprout. This is a good strategy for this typical pioneer species. Beechnuts and acorns always fall under their mother trees, so the seedlings grow in a predictable, pleasant forest microclimate, but little bird cherries can end up anywhere. Birds that gobble the tart fruit make random deposits of seeds wrapped in their own little packages of fertilizer. If a package lands out in the open in a year when the weather is extreme, temperatures will be hotter and water supplies scarcer than in the cool, damp shadows of a mature forest. Then it’s advantageous if at least some of the stowaways wait a few years before waking to their new life.

Location: 422 Every five years, a beech tree produces at least thirty thousand beechnuts (thanks to climate change, it now does this as often as every two or three years, but we’ll put that aside for the moment). It is sexually mature at about 80 to 150 years of age, depending on how much light it gets where it’s growing. Assuming it grows to be 400 years old, it can fruit at least sixty times and produce a total of about 1.8 million beechnuts. From these, exactly one will develop into a full-grown tree—and in forest terms, that is a high rate of success, similar to winning the lottery. All the other hopeful embryos are either eaten by animals or broken down into humus by fungi or bacteria.

Location: 427 Let’s consider the poplar. The mother trees each produce up to 54 million seeds—every year.17 How their little ones would love to change places with the beech tree youngsters. For until the old ones hand over the reins to the next generation, they produce more than a billion seeds.

Location: 452

Scientists have determined that slow growth when the tree is young is a prerequisite if a tree is to live to a ripe old age. As people, we easily lose sight of what is truly old for a tree, because modern forestry targets a maximum age of 80 to 120 years before plantation trees are cut down and turned into cash.

Location: 454

Under natural conditions, trees that age are no thicker than a pencil and no taller than a person. Thanks to slow growth, their inner woody cells are tiny and contain almost no air. That makes the trees flexible and resistant to breaking in storms. Even more important is their heightened resistance to fungi, which have difficulty spreading through the tough little trunks. Injuries are no big deal for such trees, either, because they can easily compartmentalize the wounds—that is to say, close them up by growing bark over them—before any decay occurs.

Location: 459

Dr. Suzanne Simard, who helped discover maternal instincts in trees, describes mother trees as dominant trees widely linked to other trees in the forest through their fungal–root connections. These trees pass their legacy on to the next generation and exert their influence in the upbringing of the youngsters.18 “My” small beech trees, which have by now been waiting for at least eighty years, are standing under mother trees that are about two hundred years old—the equivalent of forty-year-olds in human terms. The stunted trees can probably expect another two hundred years of twiddling their thumbs before it is finally their turn. The wait time is, however, made bearable. Their mothers are in contact with them through their root systems, and they pass along sugar and other nutrients. You might even say they are nursing their babies.

Location: 509

The redirected power of a windstorm can tear at the base of the trunk with a force equivalent to a weight of 220 tons.19 If there is a weak spot anywhere in the tree, it will crack. In the worst-case scenario, the trunk breaks off completely and the whole crown tumbles down. Evenly formed trees absorb the shock of buffeting forces, using their shape to direct and divide these forces evenly throughout their structure. Trees that don’t follow the etiquette manual find themselves in trouble.

Location: 516

Forked trees are even more precarious. In forked trees, at a certain point, two main shoots form, and they continue to grow alongside each other. Each side of the fork creates its own crown, so in a heavy wind, both sides sway back and forth in different directions, putting a great strain on the trunk where the two parted company. If this transition point is in the shape of a tuning fork or U, then usually nothing happens. Woe betide the tree, however, that has a fork in the shape of a V, with the two sides joining at a narrow angle. The fork always breaks at its narrowest point, where the two sides diverge. Because the break causes the tree distress, it tries to form thick bulges of wood to prevent further damage. Usually, however, this tactic doesn’t work, and bacteria-blackened liquid constantly bleeds from the wound.

Location: 555

THIRST IS HARDER for trees to endure than hunger, because they can satisfy their hunger whenever they want. Like a baker who always has enough bread, a tree can satisfy a rumbling stomach right away using photosynthesis. But even the best baker cannot bake without water, and the same goes for a tree: without moisture, food production stops. A mature beech tree can send more than 130 gallons of water a day coursing through its branches and leaves, and this is what it does as long as it can draw enough water up from below.

Location: 559

20 However, the moisture in the soil would soon run out if the tree were to do that every day in summer. In the warmer seasons, it doesn’t rain nearly enough to replenish water levels in the desiccated soil. Therefore, the tree stockpiles water in winter.

Location: 562

Together with belowground accumulation of spring showers, the stockpiled water usually lasts until the onset of summer. But in many years, water then gets scarce. After a couple of weeks of high temperatures and no rain, forests usually begin to suffer. The most severely affected trees are those that grow in soils where moisture is usually particularly abundant. These trees don’t know the meaning of restraint and are lavish in… Some highlights have been hidden or truncated due to export limits.

Location: 566

In the forest I manage, the stricken trees are usually spruce, which burst not at every seam but certainly along their trunks. If the ground has dried out and the needles high up in the crown are still demanding water, at some point, the tension in the drying wood simply becomes too much for the tree to bear. It crackles and pops, and a tear about 3 feet long opens in its bark. This tear penetrates deep into the tissue and severely injures the tree. Fungal spores… Some highlights have been hidden or truncated due to export limits.

Location: 573

Splits in its wood, in its bark, in its extremely sensitive cambium (the life-giving layer under the bark): it doesn’t get any worse than this for a tree. It has to react, and it does this not only by attempting to seal the wound. From then on, it will also do a better job of rationing water instead of pumping whatever is available out of the ground as soon as spring hits without giving a second thought to waste. The tree takes the lesson to heart, and from then on… Some highlights have been hidden or truncated due to export limits.

Location: 577

it is spruce growing in areas with abundant moisture that are affected in this way: they are spoiled. Barely half a mile away, on a dry, stony, south-facing slope, things look very different. At first, I had expected damage to the spruce trees here because of severe summer drought. What I observed was just the opposite. The tough trees that grow on this slope are well versed in the practices of denial and can withstand far worse conditions than their colleagues who are spoiled for water. Even though there is much less water available here year round—because the soil retains less water and the sun burns much hotter—the spruce… Some highlights have been hidden or truncated due to export limits.

Location: 583

Trees don’t like to make things unnecessarily difficult. Why bother to grow a thick, sturdy trunk if you can lean comfortably against your neighbors? As long as… Some highlights have been hidden or truncated due to export limits.

Location: 588

Trees are not known for their speed, and so it takes three to ten years before they stand firm once again after such disruptions. The process of learning stability is triggered by painful micro-tears that occur when the trees bend way over in the wind, first in one direction and then in the other. Wherever it hurts, that’s where the tree must strengthen its support structure. This takes a whole lot of energy, which is then unavailable for growing upward. A small consolation is the additional light that is now available for the tree’s own crown, thanks to the loss of its neighbor. But, here again, it takes a number of years for the… Some highlights have been hidden or truncated due to export limits.

Location: 594

Because the buds for the coming year are formed the previous spring and summer, it takes a deciduous tree at least two growing seasons to adjust. Conifers take even longer, because their needles stay on their branches for up to ten years. The situation… Some highlights have been hidden or truncated due to export limits.

Location: 596

The thickness and stability of a trunk, therefore, build up as the tree responds to a series of aches and pains. In a natural forest, this little game can be repeated many times over the lifetime of a tree. Once the gap opened by the loss of another tree is overcome and everyone has extended their crowns so far out that the window of light into the forest is, once again, closed, then everyone can go back to leaning on everyone else. When that happens, more energy is put into… Some highlights have been hidden or truncated due to export limits.

Location: 611

At least as far as water is concerned, there is research in the field that reveals more than just behavioral changes: when trees are really thirsty, they begin to scream. If you’re out in the forest, you won’t be able to hear them, because this all takes place at ultrasonic levels. Scientists at the Swiss Federal Institute for Forest, Snow, and Landscape Research recorded the sounds, and this is how they explain them: Vibrations occur in the trunk when the flow of water from the roots to the leaves is interrupted. This is a purely mechanical event and it probably doesn’t mean anything.22 And yet?

Location: 618

Particularly in conjunction with the crackling roots I mentioned earlier, it seems to me that these vibrations could indeed be much more than just vibrations—they could be cries of thirst. The trees might be screaming out a dire warning to their colleagues that water levels are running low.

Location: 622

TREES ARE VERY social beings, and they help each other out. But that is not sufficient for successful survival in the forest ecosystem. Every species of tree tries to procure more… Some highlights have been hidden or truncated due to export limits.

Location: 624

It is the fight for water that finally decides who wins. Tree roots are very good at tapping into damp ground and growing fine hairs to increase their surface area so that they can suck up as much water as possible. Under normal circumstances, that is sufficient, but more is always better. And that is why, for millions of years, trees have paired up with fungi. Fungi are amazing. They don’t really conform to the one-size-fits-all system we use to classify living organisms as either animals or plants.… Some highlights have been hidden or truncated due to export limits.

Location: 631

Fungi are in between animals and plants. Their cell walls are made of chitin—a substance never found in plants—which makes them more like insects. In addition, they cannot photosynthesize and depend on organic connections with other living beings they can feed on. Over… Some highlights have been hidden or truncated due to export limits.

Location: 633

There is a honey fungus in Switzerland that covers almost 120 acres and is about a thousand years old.23 Another in Oregon is estimated to be 2,400 years old, extends for 2,000 acres, and weighs 660 tons.24 That makes fungi the largest known living organisms in the world. The two aforementioned giants are not tree friendly; they kill them as they prowl the forest in… Some highlights have been hidden or truncated due to export limits.

Location: 637

With the help of mycelium of an appropriate species for each tree—for instance, the oak milkcap and the oak—a tree can greatly increase its functional root surface so that it can suck up considerably more water and nutrients. You find twice the amount of life-giving nitrogen and phosphorus in plants that cooperate with fungal partners than in plants that tap the soil with their roots alone. To enter into a partnership with one of the many… Some highlights have been hidden or truncated due to export limits.

Location: 642

From then on, the two partners work together. The fungus not only penetrates and envelops the tree’s roots, but also allows its web to roam through the surrounding forest floor. In so doing, it extends the reach of the tree’s own roots as the web grows out toward other trees. Here, it connects with other trees’ fungal partners and roots. And so a network is created, and now it’s easy for the trees to exchange food.

Location: 646

This connection makes fungi something like the forest Internet. And such a connection has its price. As we know, these organisms—more like animals in many ways—depend on other species for food. Without a supply of food, they would, quite simply, starve. Therefore, they demand payment in the form of sugar and other carbohydrates, which their partner tree has to deliver.

Location: 650

in a situation where you are so dependent on another species, to leave nothing to chance. And so the delicate fibers begin to manipulate the root tips they envelop. First, the fungi listen in on what the tree has to say through its underground structures.

Location: 653

Fungi provide a few complimentary benefits for the tree, such as filtering out heavy metals, which are less detrimental to the fungi than to the tree’s roots. These diverted pollutants turn up every fall in the pretty fruiting bodies we bring home in the form of porcini, cèpe, or bolete mushrooms.

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Medical services are also part of the package. The delicate fungal fibers ward off all intruders, including attacks by bacteria or destructive fellow fungi. Together with their trees, fungi can live to be many hundreds of years old, as long as they are healthy. But if conditions in their environment.

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Fungi are much more sensitive. Many species seek out trees that suit them, and once they have reserved them for themselves, they are joined to them for better or for worse. Species that like only birches or larches, for instance, are called “host specific.” Others, such as chanterelles, get along with many different trees: oaks, birches, and spruce. What is important is whether there is still a bit of room underground. And competition is fierce. In oak forests alone, more than a hundred different species of fungi may be present in different parts of the roots of the same tree.

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Dr. Suzanne Simard discovered that their networks are connected not only to a specific tree species but also to trees of different species.27 Simard injected into a birch tree radioactive carbon that moved through the soil and into the fungal network of a neighboring Douglas fir. Although many species of tree fight each other mercilessly above ground and even try to crowd out each other’s root systems, the fungi that populate them seem to be intent on compromise.

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They photosynthesize, they produce hydrocarbons, which fuel their growth, and over the course of their lives, they store up to 22 tons of carbon dioxide in their trunks, branches, and root systems. When they die, the same exact quantity of greenhouse gases is released as fungi and bacteria break down the wood, process the carbon dioxide, and breathe it out again. The assertion that burning wood is climate neutral is based on this concept. After all, it makes no difference if it’s small organisms reducing pieces of wood to their gaseous components or if the home hearth takes on this task, right? But how a forest works is way more complicated than that. The forest is really a gigantic carbon dioxide vacuum that constantly filters out and stores this component of the air.

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Spreadsheets that estimate lumber production need to be adjusted now that one third more biomass is accruing than a few decades ago. But what was that again? If you are a tree, slow growth is the key to growing old. Growth fueled by hefty additions of excess nitrogen from agricultural operations is unhealthy. And so the tried and tested rule holds true: less (carbon dioxide) is more (life-span).

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Researchers looked at about 700,000 trees on every continent around the world. The surprising result: the older the tree, the more quickly it grows. Trees with trunks 3 feet in diameter generated three times as much biomass as trees that were only half as wide.42 So, in the case of trees, being old doesn’t mean being weak, bowed, and fragile. Quite the opposite, it means being full of energy and highly productive. This means elders are markedly more productive than young whippersnappers, and when it comes to climate change, they are important allies for human beings. Since the publication of this study, the exhortation to rejuvenate forests to revitalize them should at the very least be flagged as misleading. The most that can be said is that as far as marketable lumber is concerned, trees become less valuable after a certain age. In older trees, fungi can lead to rot inside the trunk, but this doesn’t slow future growth one little bit. If

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With their annual leaf fall, the beeches created an alkaline humus that could store a lot of water. In addition, the air in this little forest gradually became moister, because the leaves of the growing beeches calmed the air by reducing the speed of the wind blowing through the trunks of the pines. Calmer air meant less water evaporated. More water allowed the beeches to prosper, and one day they grew up and over the tops of the pines. In the meantime, the forest floor and the microclimate had both changed so much that the conditions became more suited to deciduous trees than to the more frugal conifers. This transformation is a good example of what trees can do to change their environment. As foresters like to say, the forest creates its own ideal habitat.

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students from RWTH Aachen discovered just how great the temperature differences can be between a coniferous plantation that is regularly thinned and a beech forest that has been allowed to age naturally. On an extremely hot August day that chased the thermometer up to 98 degrees Fahrenheit, the floor of the deciduous forest was up to 50 degrees cooler than that of the coniferous forest, which was only a couple of miles away. This cooling effect, which meant less water lost, was very clearly because of the biomass, which also contributed shade. The more living and dead wood there is in the forest, the thicker the layer of humus on the ground and the more water is stored in the total forest mass. Evaporation leads to cooling, which, in turn, leads to less evaporation. To put it another way, in summer an intact forest sweats for the same reason people do and with the same result.

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For every square yard of forest, 27 square yards of leaves and needles blanket the crowns.43 Part of every rainfall is intercepted in the canopy and immediately evaporates again. In addition, each summer, trees use up to 8,500 cubic yards of water per square mile, which they release into the air through transpiration. This water vapor creates new clouds that travel farther inland to release their rain. As the cycle continues, water reaches even the most remote areas. This water pump works so well that the downpours in some large areas of the world, such as the Amazon Basin, are almost as heavy thousands of miles inland as they are on the coast.

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There are a few requirements for the pump to work: from the ocean to the farthest corner, there must be forest. And, most importantly, the coastal forests are the foundations for this system. If they do not exist, the system falls apart. Scientists credit Anastassia Makarieva from Saint Petersburg in Russia for the discovery of these unbelievably important connections.44 They studied different forests around the world and everywhere the results were the same. It didn’t matter if they were studying a rain forest or the Siberian taiga, it was always the trees that were transferring life-giving moisture into land-locked interiors. Researchers also discovered that the whole process breaks down if coastal forests are cleared. It’s a bit like if you were using an electrical pump to distribute water and you pulled the intake pipe out of the pond. The fallout is already apparent in Brazil, where the Amazonian rain forest is steadily drying out.

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The feared bark beetle basically goes for broke, seeking out weakened trees and trying to move in. Bark beetles live by the principle “all or nothing.” Either a single beetle mounts a successful attack and then sends out a scented invitation for hundreds of its kin to come on over and they kill the tree. Or the tree kills the first beetle that bores into it and the buffet is canceled for everyone. The coveted prize is the cambium, the actively growing layer between the bark and the wood. This is where the trunk grows as wood cells form on the inside and bark cells form on the outside. The cambium is succulent and stuffed full of sugar and minerals.

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Healthy spruce defend themselves with terpenes and phenols, which can kill the beetles. If that doesn’t work, they dribble out sticky resin to trap them. But researchers in Sweden have discovered that the beetles have been arming themselves. Yet again, the weapons are fungi. These fungi are found on the beetles’ bodies. As the beetles make their tunnels, the fungi come along for the ride and end up under the bark. Here, they disarm the spruce’s chemical defenses by breaking them down into harmless substances. Because the fungi grow faster than the beetles drill, once they make it under the bark, they are always one step ahead. This means all the terrain the bark beetles encounter has been decontaminated and they can feed safely.

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Even if one day the tree gives up and breaks off in a storm, it has still served the community well. Even though scientists haven’t fully researched the relationships yet, we do know that higher species diversity stabilizes the forest ecosystem. The more species there are around, the less chance there is that a single one will take over to the detriment of the others, because there’s always a candidate on hand to counteract the menace. And even the dead tree trunk can offer a valuable service managing water for living trees merely because it is there, as we’ve already seen in chapter 17, “Woody Climate Control.”

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Even though there are many beautiful sunny days they could make use of before October, they begin to turn red. And what that means is that they are shutting up shop for the year. The storage spaces under their bark and in their roots are full. If they made more sugar, there would be nowhere to stash it. While the bears happily go on eating, for these trees the sandman is already knocking on the door.

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Most other tree species seem to have larger storage areas, and they continue to photosynthesize hungrily and without taking a break right until the first hard frosts. Then they, too, must stop and shut down all activity. One reason for this is water. It must be liquid for the tree to work with it. If a tree’s “blood” freezes, not only does nothing work, but things can also go badly wrong. If wood is too wet when it freezes, it can burst like a frozen water pipe. This is the reason most species begin to gradually reduce the moisture content in their wood—and this means cutting back on activity—as early as July.

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They use the last warm days of late summer to store energy, and second, most species still need to fetch energy reserves from the leaves and get them back into their trunk and roots. Above all, they need to break down their green coloring, chlorophyll, into its component parts so that the following spring they can send large quantities of it back out to the new leaves. As this pigment is pumped out of the leaves, the yellow and brown colors that were there all along predominate. These colors are made of carotene and probably serve as alarm signals. Around this time, aphids and other insects are seeking shelter in cracks in the bark, where they will be protected from low temperatures.

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brightly colored fall leaves.51 Aphids & Co. recognize these trees as unfavorable places for their offspring because they will probably be particularly vigorous about producing toxins. Therefore, they search out weaker, less colorful trees.

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noses at the idea of an annual makeover. To protect its needles from freezing, a conifer fills them with antifreeze. To ensure it doesn’t lose water to transpiration over the winter, it covers the exterior of its needles with a thick layer of wax. As an extra precaution, the skin on its needles is tough and hard, and the small breathing holes on the underside are buried extra deep. All these precautions combine to prevent the tree from losing any significant amount of water. Such a loss would be tragic, because the tree wouldn’t be able to replenish supplies from the frozen ground. It would dry out and could then die of thirst.

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In an intact forest, every tree gets help. As the crowns swing back up, they hit each other, because each of them is straightening up at its own pace. While some are still moving backwards, others are already swinging forward again. The result is a gentle impact, which slows both trees down. By the time the next gust of wind comes along, the trees have almost stopped moving altogether and the struggle begins all over again. I never tire of watching tree crowns move back and forth.

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Snow makes it imperative that deciduous trees drop their leaves in a timely manner. Once the aforementioned 1,200 square yards of leaf surface have disappeared, the white blanket has no place to land but on the branches, and this means that most of it falls through onto the ground.

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Dropping leaves is an effective protective strategy that seems made to measure for the climate in Central European latitudes. It is also an opportunity for trees to finally excrete waste. Just as we take a trip to a quiet little room before we go to bed, trees also rid themselves of substances they do not need and would like to part with. These drift down to the ground in their discarded leaves. Shedding leaves is an active process, so the tree can’t go to sleep yet. After the reserve supplies have been reabsorbed from the leaves back into trunk, the tree grows a layer of cells that closes off the connection between the leaves and the branches. Now all it takes is a light breeze, and the leaves drift down to the ground. Only when that process is complete can trees retire to rest. And this they must do to recuperate from the exertions of the previous season.

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Sleep deprivation affects trees and people in much the same way: it is life threatening. That’s why oaks and beeches can’t survive if we try to grow them in containers in our living rooms. We don’t allow them to get any rest there, and so most of them die within the first year. Young trees standing in their parents’ shadow exhibit a few clear deviations from the standard strategy for shedding leaves. When the mother trees lose their leaves, sunlight suddenly floods the ground. The eager young pups are waiting for just this moment, and they take advantage of the bright light to fill up with lots of energy—and they are usually surprised by the first frosts while they are at it.

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In the spring, the young trees exploit a similar opportunity. They leaf out two weeks before the large trees, ensuring themselves a long leisurely breakfast in the sun. But how do the youngsters know when they need to get started? After all, they don’t know the date when the mother trees might leaf out. It’s warm temperatures close to the ground that give the game away. Spring really is rung in here approximately two weeks earlier than it is 100 feet higher up in the canopy. Up high, harsh winds and freezing cold nights delay the warm season for a little while longer. It’s the protective canopy created by the branches of the old trees that keeps heavy, late frosts from reaching the ground. At the same time, the layer of leaves covering the soil acts like a warming compost pile.

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Fungi and bacteria at the base of the trees recycle the discarded leaves to produce the raw materials the alders need to build chlorophyll, and all the trees need to do is take these building blocks up through their roots. They don’t even have to worry about recycling nitrogen, thanks to the symbiotic relationship they have with bacteria in nodules on their roots, which constantly provide them with all the nitrogen they need. Per year and square mile of alder forest, these tiny helpers can extract up to 87 tons of nitrogen from the…

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Yellow, orange, and red come to the fore when chlorophyll is removed, but these carotenes and anthocyanins are also broken down eventually. The oak is such a careful species that it stashes….

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conifers. I’ve given them rather short shrift so far, but there are three species that drop their leaves like deciduous trees—the larch, the bald cypress, and the dawn redwood. I have no idea why these three conifers are the only ones to follow the deciduous trees’ example. Perhaps in the evolutionary competition the best way to overwinter has simply not yet been decided.

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Pines especially, which shed about a quarter of their green needles, can look somewhat sparse in winter. In spring, a new year’s worth of needles is added along with fresh growth, and the crowns look the picture of health once again.

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If we take a closer look, the whole thing is a big mystery, because it means that trees need something very important: a sense of time. How do they know that winter is coming or that rising temperatures aren’t just a brief interlude but an announcement that spring has arrived? It seems logical that warmer days trigger leaf growth, because this is when frozen water in the tree trunk thaws to flow once again. What is unexpected is that the colder the preceding winter, the earlier the leaves unfurl. Researchers from the Technical University of Munich (TUM) tested this in a climate-controlled laboratory.54

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Perhaps trees need freezing temperatures to get a restorative sleep in winter and that’s why they don’t get going right away in the spring. Whatever the reason, in these times of climate change, this is a disadvantage, because other species that are not …

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least. It seems the trees can count! They wait until a certain number of warm days have passed, and only then do they trust that all is well and classify the warm phase as spring.55 But warm days alone do not mean spring has arrived. Shedding leaves and growing new ones depends not only on temperature but also on how long the days are. Beeches, for example, don’t start growing until it is light for at least thirteen

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It makes sense to look for this ability in the leaves. After all, they come with a kind of solar cell, which makes them well equipped to receive light waves. And this is just what they do in the summer months, but in April the leaves are not yet out. We don’t yet understand the process completely, but it is probably the buds that are equipped with this ability. The folded leaves are resting peacefully in the buds, which are covered with brown scales to prevent them from drying out.

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A tree trunk can register light as well. Most tree species have tiny dormant buds nestled in their bark. When a neighboring tree dies and falls down, more sun gets in, which in many trees triggers the growth of these buds so… Some highlights have been hidden or truncated due to export limits.

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Rising temperatures mean it’s spring. Falling temperatures mean it’s fall. Trees are aware of that as well. And that’s why species such as oaks or beeches, which are native to the Northern Hemisphere, adapt to reversed cycles in the Southern Hemisphere if they are exported to New Zealand and planted there. And what this proves as well, by the way, is that… Some highlights have been hidden or truncated due to export limits.

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Trees need a sense of time for more than just their foliage. This sense is equally important for procreation. If their seeds fall to the ground in fall, they mustn’t sprout right away. If they do, two problems present themselves. First, the delicate shoots won’t have time to get woody, which means they will freeze. Second, when the weather is cold, there is very little for deer to eat and they would be only too happy to pounce on the fresh, green growth. So it’s better to sprout in the spring along with all the other plants. Therefore, seeds register cold, and only when extended warm periods follow hard frost do the baby trees dare to come out of their protective coverings.

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Under normal circumstances, a tree carefully apportions its energy. The largest portion is used for daily living: the tree has to breathe, “digest” its food, supply its fungal allies with sugar, and grow a bit every day. Then the tree has to keep hidden reserves of energy on hand to fight off pests. These secret reserves can be activated at any time, and depending on the tree species, they contain a selection of defensive compounds produced by the tree. These so-called phytoncides have antibiotic properties, and there has been some impressive research done on them.

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A biologist from Leningrad, Boris Tokin, described them like this back in 1956: if you add a pinch of crushed spruce or pine needles to a drop of water that contains protozoa, in less than a second, the protozoa are dead. In the same paper, Tokin writes that the air in young pine forests is almost germfree, thanks to the phytoncides released by the needles.56 In essence, then, trees disinfect their surroundings. But that isn’t all. Walnuts have compounds in their leaves that deal so effectively with insects that garden lovers are often advised to put a bench under a canopy of walnuts if they want a comfortable place to relax in the garden, because this is where they will have the least chance of being bitten by mosquitoes.

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Often that is not enough, as the trees either act like umbrellas (Spruce & Co.) or their branches funnel the water down to their roots (deciduous trees). In the latter case, the solution is simple: mosses move into places on the trunk where the water trickles down after a shower. It’s not an even distribution because most trees are tilted slightly to one side. A small stream forms on the upper side of a slight bend, and that’s what the moss taps into. Incidentally, that is why you can’t rely on moss if you want to figure out compass directions. In climates where there is rain year round, moss supposedly indicates the weather side of the tree, where the trunk gets wet when the rain hits it; however, in the middle of the forest, where the wind is stilled, rain usually falls vertically. In addition, each tree is bent in a slightly different direction, so if you were to orient yourself according to moss, you’d only end up confused.

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Moss doesn’t damage the tree, and the tiny plants compensate for the small amount of water they divert by releasing moisture as well, so their influence on the forest climate is positive. We’re left with the question of where moss gets its food. If food doesn’t come from the ground, the only place it can come from is the air. And a whole lot of dust is blown through forests every year. A mature tree can filter out more than 200 pounds, which rain flushes down the trunk. Mosses soak up the dusty mixture and filter out what they can use. That deals with the food, and now the only thing missing is light. In bright pine or oak forests, light isn’t a problem, but it is in those eternally dark spruce forests. Even the most abstemious must give these a miss, and that’s why particularly dense stands of young trees in coniferous forests are most often completely moss free. It is only as the trees age, when here and there gaps appear in the canopy, that enough sunlight filters through for the trees to get a covering of moss.

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Sometimes there’s no rain for months on end. If you run your fingers over a cushion of moss in a dry spell, you’ll find it is completely desiccated. Most plants would die at this stage, but not moss. It swells with the next heavy rain shower—and life continues. Lichen are even more frugal. These small gray-green growths are a symbiotic combination of fungi and algae. To hold together, they need some kind of a substrate, and in the forest, this is provided by trees. In contrast to moss, they climb much higher up the trunks, where their already extremely slow growth is slowed still further by the leafy canopy.

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(Trees in parks). They just seem to be putting their energy into growing in the wrong direction. Their location gives a clue as to why this might be the case. They were often planted in city parks by princes and politicians as exotic trophies. What is missing here, above all, is the forest, or—more specifically—relatives. At 150 years old, they are, when you consider a potential life-span of many thousands of years, indeed only children, growing up here in Europe far from their home and without their parents. No uncles, no aunts, no cheerful nursery school—no, they have lived all their lives out on a lonely limb.

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What about the many other trees in the park? Don’t they form something like a forest, and couldn’t they act like surrogate parents? They usually would have been planted at the same time and so could offer the little redwoods no assistance or protection. In addition, they are very, very different kinds of trees. To let lindens, oaks, or beeches bring up a redwood would be like leaving human children in the care of mice, kangaroos, or humpback whales. It just doesn’t work, and the little Americans have had to fend for themselves. No mother to nurse them or keep a strict eye out to make sure the little ones didn’t grow too quickly. No cozy, calm, moist forest around them. Nothing but solitude.

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And if that weren’t enough, in most cases, the soil is a complete disaster. 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. What’s more, members of the public like to walk up to the trees, touch their bark, and relax in the shadow of their crowns. Over the decades, constant trampling around the base of the trees leads to further soil compaction.

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The mechanics of planting also haunt the trees for the rest of their lives. They are kept alive and handled in nurseries for years before being moved to their final locations. Every fall, their roots are trimmed to keep them compact in the nursery beds so that they can later be moved more easily. The root ball, which for a 10-foot-tall tree grows to about 20 feet in diameter if left to its own devices, is cut back to about 20 inches, and to make sure the crown doesn’t wilt from thirst thanks to the root reduction, it too is heavily reduced. All this is done not to improve the health of the tree (but to improve its ability to be taken, picked up and transported)….

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After that, it is as if this interference makes the trees lose their sense of direction underground. They stop growing roots down into the soil and form a flat plate of roots near the surface instead, severely restricting the trees’ ability to find water and food. At first, the young trees don’t seem to mind. They stuff themselves with sugary treats because they can photosynthesize as much as they like in full sun. It’s so easy to get over the loss of a mother’s tender care. And in the early years, the water problems in a rock-hard soil are barely noticeable. After all, the saplings are being lovingly cared for and watered by gardeners when they get dry.

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Every young tree can do just as it likes. So, every year, they go at it as though they were in a race, and every year, they put on a growth spurt. After a certain height, the childhood bonus seems to run out. Irrigating 65-foot-tall trees takes an enormous amount of water and time. To thoroughly moisten the roots, the gardeners must spray… Some highlights have been hidden or truncated due to export limits.

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At first, the giant redwoods don’t really notice. They’ve lived high on the hog for decades and done whatever they wanted. Their thick trunks are like paunches attesting to an orgy of solar indulgence. In the early years, it doesn’t really matter much that the cells inside their trunks are very large.

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A severely pruned crown is a severe blow for the roots, which grow to a size optimally suited to serve the above-ground parts of the tree. If a large percentage of the branches is removed and the level of photosynthesis drops, then just as large a percentage of the underground part of the tree starves. Fungi now penetrate the dead ends where branches have been removed and the trunk has been sawn off. The wood is filled with air pockets, thanks to the tree’s quick growth as a youngster, and fungi have a field day. After only a few decades—which is incredibly fast for a tree—this inner rot can also be seen on the outside of the tree.

The waxy substance painted over the damaged trunk,

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Whereas forests cool themselves on hot summer nights, streets and buildings radiate the heat they soaked up during the day, keeping temperatures elevated. Radiated heat makes the air extremely dry. Not only that, but it’s full of exhaust fumes. Many of the companions that look after trees’ well-being in the forest (such as the microorganisms that make humus) are missing. Mycorrhizal fungi that help collect water and food are present only in low numbers. Urban trees, therefore, have to go it alone under the harshest conditions. As if that were not enough, they also have to deal with unsolicited extra fertilizers. Above all, from dogs, which lift their legs at every available trunk. Their urine can burn bark and kill roots. Winter salt leads to similar damage.

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The needles on conifers, which are still attached to the branches in winter, have to deal with the salt spray thrown up by car tires. At least 10 percent of the salt ends up in the air and falls back down on trees—among other resting places—where it burns the foliage. These painful injuries show up as small yellow and brown spots on the needles. The burns reduce the trees’ ability to photosynthesize the next summer and, therefore, weaken the trees. Weakness equals pests. It’s easier for scales and aphids to strike, because street trees have limited resources they can put toward defending themselves. High urban temperatures are a contributing factor. Hot summers and warm winters favor the insects, which survive in larger numbers.

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At the end of the day, the stresses the trees must bear are so great that most of them die prematurely. Even though they can do whatever they want when they’re young, this freedom is not enough to compensate for the disadvantages they face later in life. One consolation is that because streets and pathways are often planted with rows of the same species of trees, at least they are able to communicate with other members of their species. Plane trees—recognizable by their attractive bark, which peels off in colorful flakes—are a popular choice for these regimented plantings. Whatever it is these street kids talk to each other about through their scent-mail—and whether the tone of these messages is as rough as their lives—the street gangs are keeping this information strictly to themselves.

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An open space, however, is attractive to herbivores, because it’s not only trees that try their luck here but also grasses and wild flowers, which don’t do well in the forest understory. Deer—or, in earlier times, wild horses, aurochs, and bison—are drawn to these plants. Grasses are adapted to constant grazing and are relieved that the young trees that threaten their existence are being polished off in the process. Many shrubs that would dearly love to grow taller than the grasses have developed dangerous thorns to protect themselves from the voracious beasts.

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Silver birch bark has another surprise in store. The white color is because of the active ingredient betulin, its primary component. White reflects sunlight and protects the trunk from sunscald. It also guards the trunk against heating up in the warming rays of the winter sun, which could cause unprotected trees to burst. As birches are pioneer trees that often grow all alone in wide-open spaces without any neighbors to shade them, such a feature makes sense. Betulin also has antiviral and antibacterial properties and is an ingredient in medicines and in many skin care products.60

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What’s really surprising is how much betulin there is in birch bark. A tree that makes its bark primarily out of defensive compounds is a tree that is constantly on the alert. In such a tree there is no carefully calibrated balance between growth and healing compounds. Instead, defensive armoring is being thrown up at a breakneck pace everywhere. Why doesn’t every species of tree do that? Wouldn’t it make sense to be so thoroughly prepared against attack that potential aggressors would breathe their last the moment they took the first bite? Species that live in social groups don’t entertain this option because every individual belongs to a community that will look after it in times of need, warn it of impending dangers, and feed it when it is sick or in distress.

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Cutting back on defense saves energy, which the tree can then invest in producing wood, leaves, and fruit. Not so with the birches, which must be completely self-reliant if they are to survive. But they, too, grow wood—and indeed, they do so a lot faster—and they, too, want to, and do, reproduce. Where does all their energy come from? Can this species somehow photosynthesize more efficiently than others? No. The secret, it turns out, lies in wildly overtaxing their resources. Birches rush through life, live beyond their means, and eventually wear themselves out.

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One broken-off branch is enough to provide a port of entry. Because their wood is composed of large cells grown in haste, it contains a lot of air, and so the destructive fungal filaments can spread quickly. The trunk rots big time, and because pioneer species often stand out in the open alone, it’s not long until the next fall storm topples the tree. This is not a tragedy for the species itself. Its goal of rapid dispersal was achieved a long time ago, as soon as it quickly reached sexual maturity and propagated.

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seeds that progressed north, mile by mile. The average speed of the beeches’ journey, by the way, is about a quarter mile—a year.

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The silver fir, like most tree species, waited out the ice age in southern Europe, probably in Italy, the Balkans, and Spain.62 It migrated from there, following the other trees, at a rate of 300 yards a year. Spruce and pines pulled ahead because their seeds are considerably lighter and better fliers. Even the beeches with their heavy nuts were faster, thanks to the jays.

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Cool summers are followed by warm winters, and precipitation is between 20 and 60 inches a year, just the way beeches like it. Water is one of the key factors for growth in the forest, and this is where the beeches score big time. To produce 1 pound of wood, they need 22 gallons of water. Does this sound like a lot? Most other species of tree need up to 36 gallons, almost twice as much, and that is the deciding factor that enables beeches to shoot up quickly and suppress other species. Spruce are predisposed to guzzle water because in their cool, moist comfort zone in far northern regions, drought is unheard of. In Central Europe, only zones just below the tree line offer the conditions spruce enjoy. It rains a lot here, and thanks to the low temperatures, there’s hardly any evaporation. Trees growing at these elevations can afford to waste water. In most lower-lying areas, however, the frugal beeches come out ahead.

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A large construction site near Zurich shows just how abrupt. Workers here came across relatively fresh tree stumps, which, at first, they set aside without paying them any attention. A researcher found them, took samples, and investigated their age. The result: the stumps came from pines that were growing there almost fourteen thousand years ago. Even more amazing, though, were the fluctuations in temperature at that time. In less than thirty years, the temperature dropped as much as 42 degrees Fahrenheit, only to finally rise again by about the same amount. That corresponds to the current worst-case climate change scenario we could potentially face by the end of the twenty-first century. Even the last century in Europe, with the bitterly cold 1940s, the record drought in the 1970s, and the way-too-warm 1990s, was very hard on Nature. Trees employ two strategies to stoically endure these changes: behavior and genetic variability.

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because they have no legs to carry them away and nowhere to turn for help, they have to adapt so that they can deal with the situation themselves. The first opportunity to do this comes at the very earliest stage of life. Shortly after fertilization, when the seeds are ripening in the flower, they react to environmental conditions. If it is particularly warm and dry, appropriate genes are activated. Scientists have proved that under these conditions, spruce seedlings are better able to tolerate warm weather—though they lose the same measure in frost resistance.63

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Mature trees can adapt as well. If spruce survive a dry period with little water, in the future they are markedly more economical with moisture and they don’t suck it all up out of the ground right at the beginning of summer. The leaves and needles are the organs where most water is lost through transpiration. If the tree notices that water is in short supply and thirst is becoming a long-term problem, it puts on a thicker coat. The tree toughens up the protective waxy layer on the upper surface of its leaves. The walls of the cells within the leaves keep them watertight, and the tree increases the thickness of the cell walls by adding extra layers. As the tree battens down the hatches, however, it also has a harder time breathing.

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Once a tree has exhausted its behavioral repertoire, genetics come into play. As I’ve just mentioned, it takes an extremely long time to produce a new generation of trees. This means speedy adaptation is not an option, but other responses are available. In a forest that has been left to its own devices, the genetic makeup of each individual tree belonging to the same species is very different. This is in contrast to people, who are genetically very similar. In evolutionary terms, you could say we are all related. In contrast, the individual beeches growing in a stand near where I live are as far apart genetically as different species of animals. This means each tree has different characteristics. Some deal better with drought than cold. Others have powerful defenses against insects. And yet others are perhaps particularly impervious to wet feet.… Some highlights have been hidden or truncated due to export limits.

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If conditions become more extreme, one tree species could even be decimated without this being the end of the forest. Usually, a sufficiently large number of trees remain to produce enough fruit and shade for the next generation. I made a calculation for the old beech stands in the forest I manage using available scientific data. Even if we were to have a Spanish-style climate here in Hümmel sometime in the future, an overwhelming number of the trees would cope. The only proviso is that the social structure… Some highlights have been hidden or truncated due to export limits.

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Douglas firs, which are native to North America but now grow in Central Europe as well, react in much the same way as oaks, but in their case, their roots seem to be super sensitive. In the forest I manage I’ve observed two lightning strikes where not only the tree that was struck died, but another ten Douglas firs within a radius of 50 feet of the strike experienced the same fate. Clearly, the surrounding trees were connected to the victim underground, and that day, instead of life-giving sugar, what they received was a deadly serving of electricity.

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North American mothers need much more light and perish in the kindergartens established by our native deciduous trees. It is only when people lend a helping hand by repeatedly clearing trees so that sunlight reaches the ground that the little Douglas firs stand a chance. It’s dangerous when foreigners pop up that are genetically very similar to native species. The Japanese larch is just such a case. When it arrived here, it met the European larch. The European larch often grows crooked and, in addition, quite slowly, and so in the last century it was often replaced with the Japanese tree. Both species cross easily to form hybrids. This raises the danger that one day, a long time from now, the last purebred European larches will disappear. There’s just such a mixing and muddling of genes going on in the forest I manage in the Eifel mountains, where neither species is native. Another candidate for extinction is the black poplar, which mixes with cultivated hybrid poplars that have been crossed with Canadian poplars. But most introduced species pose no threat to native trees. Without our help, a number of them would have disappeared again after a couple of hundred years at the most. Even with our help, the survival of the new arrivals is questionable in the long term. For the pests that plague them take advantage of global trade. It is true that there is no active import of these organisms—after all, who would want to introduce damaging pests? Yet, slowly but surely, fungi and insects are making their way across the Atlantic or the Pacific in imported lumber and establishing themselves in Europe. Often they come in packing materials, such as wood pallets that haven’t been heated to sufficiently high temperatures to kill harmful organisms. And parcels sent by private individuals from overseas sometimes contain living insects. I have personal experience of this. I had an antique moccasin from North America shipped to my home in Germany. As I unpacked the leather footwear from its newspaper wrapping, a number of small brown beetles crawled in my direction. I caught them as quickly as I could, squished them, and disposed of them in the trash. Squishing bugs might sound odd coming from the pen of a conservationist, but introduced insects, once they get established, are life threatening not only for introduced species but also for natives. The Asian long-horned beetle poses just such a threat. It probably traveled to Europe and other parts of the world from China in packing crates. The beetle is an inch long and has 2-inch-long antennae. To us, it’s a beautiful-looking beetle. Its dark body is flecked with white, and it has black and white bands on its legs and antennae. Deciduous trees, however, find it decidedly less attractive, because it lays its eggs individually in numerous small splits in their bark. Voracious larvae hatch and feed, and adult beetles drill thumb-sized exit holes in the trunk. These holes are then attacked by fungi, and eventually… Some highlights have been hidden or truncated due to export limits.

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Native must be understood on a much smaller scale and be based not on human borders but on habitats. Habitats are defined by their features (water, terrain, topography) and by the local climate. After the last ice age, trees moved into habitats where they found conditions that suited them. That means, for example, that spruce occur naturally (and, therefore, can be considered native) at an elevation of 4,000 feet in the Bavarian Forest, but they do not occur naturally (and, therefore, cannot be considered native) 1,300 feet lower and only half a mile away, where beeches and firs hold sway. Specialists have come up with the term “habitat specific,” which simply means each species has habitats where they are happy to grow. In contrast to our large-scale country borders, habitat borders for species are like a proliferation of small states.

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Forests differ a great deal from one another depending on the species of trees they contain. Coniferous forests noticeably reduce the number of germs in the air, which feels particularly good to people who suffer from allergies. However, reforestation programs introduce spruce and pines to areas where they are not native, and the newcomers experience substantial problems in their new habitats. Usually, they are brought to low elevations that are too warm and dry for conifers to thrive. As a result, the air is dustier, as you can clearly see when the dust motes are backlit by sun streaming down on a summer’s day. And because the spruce and pines are constantly in danger of dying of thirst, they are easy prey for bark beetles, which come along to make a meal of them. At this point, frantic scent-mails begin to swirl around in the canopy. The trees are “screaming” for help and activating their arsenal of chemical defenses. You absorb all of this with every breath of forest air you take into your lungs. Is it possible that you could unconsciously register the trees’ state of alarm?

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Threatened forests are inherently unstable, and therefore, they are not appropriate places for human beings to live. And because our Stone Age ancestors were always on the lookout for ideal places to set up camp, it would make sense if we could intuitively pick up on the state of our surroundings. There is a scientific observation that speaks to this: the blood pressure of forest visitors rises when they are under conifers, whereas it calms down and falls in stands of oaks.

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67 Korean scientists have been tracking older women as they walk through forests and urban areas. The result? When the women were walking in the forest, their blood pressure, their lung capacity, and the elasticity of their arteries improved, whereas an excursion into town showed none of these changes. It’s possible that phytoncides have a beneficial effect on our immune systems as well as the trees’ health, because they kill germs. Personally, however, I think the swirling cocktail of tree talk is the reason we enjoy being out in the forest so much. At least when we are out in undisturbed forests.… Some highlights have been hidden or truncated due to export limits.

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Possibly it’s because in ancient beech forests, fewer “alarm calls” go out, and therefore, most messages exchanged between trees are contented ones, and these messages reach our brains as well, via our noses. I am… Some highlights have been hidden or truncated due to export limits.

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Contrary to popular opinion, the air in the forest is not always particularly rich in oxygen. This essential gas is released when water and carbon dioxide are broken down during photosynthesis. Every day in summer, trees release about 29 tons of oxygen into the air per square mile of forest. A person breathes in nearly 2 pounds of oxygen a day, so that’s the daily requirement for about ten thousand people. Every walk in the forest is like taking a shower in oxygen. But only during the day. Trees manufacture large amounts of carbohydrates not only to lay them down as wood but also to satisfy their hunger. Trees use carbohydrates as fuel, just as we do, and when they do, they convert sugar into… Some highlights have been hidden or truncated due to export limits.

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that is why it is so awful for a tree if the soil around its trunk has been so compacted that the small air pockets in the soil have been crushed. The tree’s roots suffocate, or at least have difficulty breathing, with the result that the tree gets sick.

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In 1981, the German journal Gartenamt reported that 4 percent of oak deaths in one American city happened because the trees were subjected to light every night.

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The main reason we misunderstand trees, however, is that they are so incredibly slow. Their childhood and youth last ten times as long as ours. Their complete life-span is at least five times as long as ours. Active movements such as unfurling leaves or growing new shoots take weeks or even months. And so it seems to us that trees are static beings, only slightly more active than rocks.

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At the same time, some of the processes under the trunk happen much more quickly than the ones we can see. For instance, water and nutrients—that is to say, “tree blood”—flow from the roots up to the leaves at the rate of a third of an inch per second.68 Even conservationists and many foresters are victims of optical illusions in the forest. This is hardly surprising. People rely heavily on sight, and so we are particularly influenced by this sense. Thus, ancient forests in Central European latitudes often strike us as being dull and species poor when we see them for the first time. The diversity of animal life plays out mostly in the microscopic realm, hidden from the eyes of forest visitors.

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Species that live out in the open often make more noise and take less trouble to keep out of sight. Perhaps you are familiar with this behavior from your own garden, where tits and chickadees, blackbirds and robins quickly get used to you and don’t bother to hop or fly away more than a few yards when you come along. Even the butterflies in the forest are mostly brown and gray and blend in with bark when they land on a tree trunk, whereas those that fly in wide-open spaces vie with one another in such a symphony of color and iridescence that it’s almost impossible to miss them. It’s the same with the plants. Forest species are mostly small and look very much alike. There are so many hundreds of species of mosses, all tiny, that even I have lost track, and the same goes for the diversity of lichens.

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A scientific study by the Ecological Society of Germany, Austria, and Switzerland concluded that although increased forest management leads to increased richness in the diversity of plant life, this is no cause for celebration but rather proof of the level of disturbance of the natural ecosystem.69

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In the United Kingdom, the designation “ancient woodlands” affords some protection to woodlands that have existed continuously since at least the 1600s. Often formerly the property of large estates, over their history they have been intensively managed for wood and wildlife, and so, although the wood itself may be ancient, the trees that grow there may not.

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forest preserves, such as the Adirondack and Catskill parks in New York State, keep economic interests out of the forests. According to the state constitution, the preserve “shall be forever kept as wild forest lands,”… Some highlights have been hidden or truncated due to export limits.

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In the wilderness areas of these preserves, most structures are not allowed, power vehicles are banned, and chainsaws require special permits. What started as a measure to ensure that excessive logging in the nineteenth century didn’t lead to soil erosion and silting up of the economically important Erie Canal has turned into a resource… Some highlights have been hidden or truncated due to export limits.

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Great Bear Rainforest in northern British Columbia, which covers almost 25,000 square miles along the rugged coast. Half of this area is forested, including about 8,900 square miles of old-growth trees. This primeval forest is home to the rare spirit bear, which although it is white, is not a polar bear but a black bear with white fur. First Nations in the area have been fighting since the 1990s to protect their homelands. On February 1, 2016, an agreement was announced to keep 85 percent of the forest unlogged, though it does allow for 15 percent of the trees, mostly old… Some highlights have been hidden or truncated due to export limits.

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Marilyn Slett, president of Coastal First Nations, is well aware of the forest’s importance: “Our leaders understand our well being is connected to the well being of our lands and waters… If we use our knowledge and our wisdom to look after [them], they will look after us into the future.”70 The Kichwa of Sarayaku, Ecuador, see their forest as “the most exalted expression of life itself.”71 In densely populated Central Europe, the… Some highlights have been hidden or truncated due to export limits.

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There’s consensus among German politicians that 5 percent of the forests should be left to their own devices so that they can become… Some highlights have been hidden or truncated due to export limits.

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Even if only 2 percent of the forests in Germany were freed from human interference, that’s still more than 770 square miles. You could observe the free play of natural forces in such areas. In contrast to nature preserves, which are always carefully groomed, what would be preserved here would be doing absolutely nothing. In scientific terms, this is known as “process conservation.” And because Nature is… Some highlights have been hidden or truncated due to export limits.

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The future old-growth forest is just as happy to develop from a monoculture. As long as people don’t meddle, the first drastic changes can be seen after just a few years. Usually, it’s the arrival of insects, such as tiny bark beetles, which can now proliferate and spread without hindrance. The conifers were originally planted in symmetrical rows in places that were too warm and dry for them. In these conditions, they are unable to defend themselves from their attackers, and within just a few weeks, their bark is completely dead as a result of the beetles’ depredations.

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Most national parks give in to the clamor of complaint and sell to sawmills the trees they have felled and removed from the forest to combat bark beetle infestations. This is a grave mistake. For the dead spruce and pines are midwives to the new deciduous forest. They store water in their dead trunks, which help cool the hot summer air to a bearable temperature. When they fall over, the impenetrable barricade of trunks acts as a natural fence through which no deer can pass. Protected in this way, the small oaks, bird cherries, and beeches can grow up unbrowsed. And when one day the dead conifers rot, they create valuable humus.

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But you don’t have an established forest yet, because the young trees don’t have any parents. There’s no one there to slow the growth of the little ones, to protect them, or in case of emergency, to feed them sugar. The first natural generation of trees in a national park, therefore, grows up more or less like the “street kids.” Even the mix of tree species is unnatural at first. The former coniferous plantation trees sow their seeds heavily before they depart, so spruce, pines, and Douglas firs grow along with the beeches, oaks, and silver firs. It’s at this point that officials usually get impatient.

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once you understand that the first generation of trees is going to grow too quickly anyway and, therefore, is not going to get very old—and that the stable social structure of the forest is not going to be laid down until much later—then you can take a more relaxed view. The plantation trees growing in the mix will depart in less than a hundred years because they will grow above the tops of the deciduous trees and stand unprotected in the path of storms that will ruthlessly uproot them. These first gaps will be vanquished by the second generation of deciduous trees, which can now grow up protected by the leafy canopy formed by their parents. Even if these parents themselves don’t grow very old, they will still grow old enough to give their children a slow start.

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Preserves where managed forests are allowed to develop into old-growth forests have a calming effect on Nature and offer better experiences for people seeking rest and relaxation.

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as we credit our animal colleagues with increasingly complex emotional lives, we are extending rights to them, as well. In Germany, a law that improved animal rights under civil law (referred to in Germany by the shorthand TierVerbG) came into force in 1990. The goal of this legislation is to ensure that animals are no longer treated as objects. More and more people are giving up meat altogether or giving more thought to how they buy meat to promote the humane treatment of animals.

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even insects such as fruit flies. Researchers in California have discovered that even these tiny creatures might dream.73 Sympathy for flies? That’s quite a stretch for most people, and the emotional path to the forest is even more of a stretch. Indeed, the conceptual gap between flies and trees is well-nigh unbridgeable for most of us. Large plants do not have brains, they move very slowly, their interests are completely different from ours, and they live their daily lives at an incredibly slow pace. It’s no wonder that even though every schoolchild knows trees are living beings, they also know they are categorized as objects.

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Not to put too fine a point on it, we use living things killed for our purposes. Does that make our behavior reprehensible? Not necessarily. After all, we are also part of Nature, and we are made in such a way that we can survive only with the help of organic substances from other species. We share this necessity with all other animals. The real question is whether we help ourselves only to what we need from the forest ecosystem… Some highlights have been hidden or truncated due to export limits.

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That means it is okay to use wood as long as trees are allowed to live in a way that is appropriate to their species. And that means that they should be allowed to fulfill their social needs, to grow in a true forest environment on undisturbed ground, and to pass their knowledge on to the next generation. And at least some of them should be allowed to grow old with dignity and finally die a natural death. What organic farms are to agriculture, continuous cover forests with careful selective cutting are to silviculture. In these forests (… Some highlights have been hidden or truncated due to export limits.

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Occasionally, a tree is harvested with care and removed using horses. And so that old trees can fulfill their destinies, 5 to 10 percent of the area is completely protected. Lumber from forests with such species-appropriate tree management can be used with no qualms of conscience. Unfortunately, 95 percent of the current forest practice in Central… Some highlights have been hidden or truncated due to export limits.

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The public is getting increasingly involved in the management of community forests, and they are insisting the authorities embrace higher environmental standards. We have the example of “forest-friendly” Königsdorf near Cologne, which reached a mediated agreement with the forest service and the regional ministry for natural resources and the environment that heavy machinery no longer be used and deciduous trees of a great age never be cut down.74 On the other side of the Atlantic, in Virginia, the mission of the nonprofit Healing Harvest… Some highlights have been hidden or truncated due to export limits.

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In the case of Switzerland, a whole country is concerned with the species-appropriate treatment of all things green. The constitution reads, in part, that “account [is] to be taken of the dignity of… Some highlights have been hidden or truncated due to export limits.

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I, for one, welcome breaking down the moral barriers between animals and plants. When the capabilities of vegetative beings become known, and their emotional lives and needs are recognized, then the way we treat plants will gradually change, as well. Forests are not first and foremost lumber factories and warehouses for raw material, and only secondarily complex habitats for thousands of species, which is the way modern forestry currently treats them. Completely the opposite, in fact. Wherever forests can develop in a species-appropriate manner, they offer… Some highlights have been hidden or truncated due to export limits.

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the first encouraging results—such as the forest in Königsdorf—give hope that in the future forests will continue to live out their hidden lives, and our descendants will still have the opportunity to walk through the trees in wonder. This is what this ecosystem achieves: the fullness of life with tens of thousands of species interwoven and interdependent. And just how important this interconnected… Some highlights have been hidden or truncated due to export limits.

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Katsuhiko Matsunaga, a marine chemist at the Hokkaido University, discovered that leaves falling into streams and rivers leach acids into the ocean that stimulate the growth of plankton, the first and most important building block in the food chain. More fish because of the forest? The researcher encouraged the planting of more trees in… Some highlights have been hidden or truncated due to export limits.

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THE UNDERGROUND SOCIAL networks of trees that Peter Wohlleben describes in his home woodlands of Germany were discovered in the inland temperate rainforests of western North America. In the early 1990s, when searching for clues to the remarkable fertility of these Pacific forests, we unearthed a constellation of fungi linking manifold tree species. The mycelial web, as we later discovered, was integral to the life of the forest. Peter’s account that these networks, as in our old-growth forests, are also important to the wellbeing of the beech, oak, and planted spruce forests of Europe is heartening.

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In pulling back the forest floor using microscopic and genetic tools, I discovered that the vast belowground mycelial network was a bustling community of mycorrhizal fungal species. These fungi are mutualistic. They connect the trees with the soil in a market exchange of carbon and nutrients and link the roots of paper birches and Douglas firs in a busy, cooperative Internet. When the interwoven birches and firs were spiked with stable and radioactive isotopes, I could see, using mass spectrometers and scintillation counters, carbon being transmitted back and forth between the trees, like neurotransmitters firing in our own neural networks. The trees were communicating through the web!

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I was staggered to discover that Douglas firs were receiving more photosynthetic carbon from paper birches than they were transmitting, especially when the firs were in the shade of their leafy neighbors. This helped explain the synergy of the pair’s relationship. The birches, it turns out, were spurring the growth of the firs, like carers in human social networks. Looking further, we discovered that the exchange between the two tree species was dynamic: each took different turns as “mother,” depending on the season. And so, they forged their duality into a oneness, making a forest. This discovery was published by Nature in 1997 and called the “wood wide web.”

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The wood wide web has been mapped, traced, monitored, and coaxed to reveal the beautiful structures and finely adapted languages of the forest network. We have learned that mother trees recognize and talk with their kin, shaping future generations. In addition, injured trees pass their legacies on to their neighbors, affecting gene regulation, defense chemistry, and resilience in the forest community. These discoveries have transformed our understanding of trees from competitive crusaders of the self to members of a connected, relating, communicating system. Ours is not the only lab making these discoveries—there is a burst of careful scientific research occurring worldwide that is uncovering all manner of ways that trees communicate with each other above and below ground.

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He describes the peculiar traits of these gentle, sessile creatures—the braiding of roots, shyness of crowns, wrinkling of tree skin, convergence of stem-rivers—in a manner that elicits an aha! moment with each chapter. His insights give new twists on our own observations, making us think more deeply about the inner workings of trees and forests. DR. SUZANNE SIMARD Professor of Forest Ecology University of British Columbia, Vancouver February 2016

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S.W. Simard, D.A. Perry, M.D. Jones, D.D. Myrold, D.M. Durall, and R. Molina, “Net Transfer of Carbon between Tree Species with Shared Ectomycorrhizal Fungi,” Nature 388 (1997): 579–82. 2. E.C. Fraser, V.J. Lieffers, and S.M. Landhäusser, “Carbohydrate Transfer through Root Grafts to Support Shaded Trees,” Tree Physiology 26 (2006): 1019–23. 3. Massimo Maffei, quoted in M. Anhäuser, “The Silent Scream of the Lima Bean,” MaxPlanckResearch 4 (2007): 65, http://www.mpg.de/942876/W001_Biology-Medicine_060_065.pdf, accessed February 16, 2016. 4. Ibid., 64. 5. M. Anhäuser, “The Silent Scream of the Lima Bean,” MaxPlanckResearch 4 (2007): 62. 6. Y.Y. Song, S.W. Simard, A.Carroll, W.W. Mohn, and R.S. Zheng, “Defoliation of Interior Douglas-Fir Elicits Carbon Transfer and Defense Signalling to Ponderosa Pine Neighbors through Ectomycorrhizal Networks,” Nature, Scientific Reports 5 (2015): art. 8495; and K.J. Beiler, D.M. Durall, S.W. Simard, S.A. Maxwell, and A.M. Kretzer, “Mapping the Wood-Wide Web: Mycorrhizal Networks Link Multiple Douglas-Fir Cohorts,” New Phytologist, 185 (2010): 543–53. 7. Susanne Billig and Petra Geist, “Die Intelligenz der Pflanzen” (“The intelligence of plants”), Deutschlandradio Kultur, July 18, 2010, http://www.deutschlandradiokultur.de/die-intelligenz-der-pflanzen.1067.de.html?dram:article_id=175633, accessed December 12, 2014. 8. Tyroler Glückspilze, “Was sollte ich über die Anwendung von Mykorrhiza-Produkten wissen?” (“What should I know about using mycorrhizal products?”), http://www.gluckspilze.com/faq, accessed October 14, 2014. 9. S.W. Simard, D.A. Perry, M.D. Jones, D.D. Myrold, D.M. Durall, and R. Molina, “Net Transfer of Carbon between Tree Species with Shared Ectomycorrhizal Fungi,” Nature 388 (1997): 579–82. 10. Ibid. 11. D.A. Perry, “A Moveable Feast: The Evolution of Resource Sharing in Plant–Fungus Communities,” Trends in Ecology & Evolution 13 (1998): 432–34, and D.M. Wilkinson, “The Evolutionary Ecology of Mycorrhizal Networks,” Oikos 82 (1998): 407–10. 12. N. Lymn, “Commercial Corn Varieties Lose Ability to Communicate with Their Own Defenders,” Ecological Society of America, October 27, 2011, http://www.esa.org/esablog/research/commercial-corn-varieties-lose-ability-to-communicate-with-their-own-defenders, accessed January 26, 2016. 13. Monica Gagliano, et al., “Toward Understanding Plant Bioacoustics,” Trends in Plant Science 17(6) (June 2012): 323–25. 14. Unpublished research from RWTH Aachen. 15. Knut Sturm, district forester, Lübeck, personal communication, 2015.

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S.W. Simard, video, “Mother Tree,” in Jane Engelsiepen, “‘Mother Trees’ Use Fungal Communication Systems to Preserve Forests,” Ecology Global Network, October 8, 2012, http://www.ecology.com/2012/10/08/trees-communicate, accessed January 26, 2016, and S.W. Simard, K.J. Beiler, M.A. Bingham, J.R. Deslippe, L.J. Philip, and F.P. Teste, “Mycorrhizal Networks: Mechanisms, Ecology and Modelling,” Fungal Biology Reviews 26 (2012): 39–60.

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How much water do deciduous trees need?”), http://www.ds.mpg.de/139253/05, accessed December 9, 2014. 21. University of Western Australia, “Move Over Elephants—Plants Have Memories Too,” University News, January 15, 2014, http://www.news.uwa.edu.au/201401156399/research/move-over-elephants-mimosas-have-memories-too, accessed October 8, 2014. 22. Swiss Federal Institute for Forest, Snow, and Landscape Research WSL, “Rendering Ecophysiological Processes Audible,” http://www.wsl.ch/fe/walddynamik/projekte/trees/index_EN, accessed January 26, 2016. 23. Swiss Federal Institute for Forest, Snow, and Landscape Research WSL, “Grösster Pilz der Schweiz” (“Largest fungus in Switzerland”), http://www.wsl.ch/medien/presse/pm_040924_DE, May 27, 2010, accessed December 18, 2014. 24. A. Casselman, “Strange but True: The Largest Organism on Earth Is a Fungus,” Scientific American, October 4, 2007, http://www.scientific-american.com/article/strange-but-true-largest-organism-is-fungus, accessed January 26, 2016.

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SCINEXX, “Forscher belauschen Gespräche zwischen Pilz und Baum” (“Researchers eavesdrop on conversations between fungi and trees”), January 23, 2008, http://www.scinexx.de/wissen-aktuell-7702-2008-01-23.html, accessed October 13, 2014. 27. S.W. Simard, D.A. Perry, M.D. Jones, D.D. Myrold, D.M. Durall, and R. Molina, “Net Transfer of Carbon between Tree Species with Shared Ectomycorrhizal Fungi.” Nature 388 (1997): 579–82. 28. J. Fraser, “Root Fungi Can Turn Pine Trees into Carnivores—Or at Least Accomplices,” Scientific American, May 12, 2015, blogs.scientificamerican.com/artful-amoeba/root-fungi-can-turn-pine-trees-into-carnivores-8212-or-at-least-accomplices, accessed January 26, 2016. 29.

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  1. Owen, “Oldest Living Tree Found in Sweden,” National Geographic News, April 14, 2008, news.nationalgeographic.com/news/2008/04/080414-oldest-tree.html, accessed January 26, 2016. 34. František Baluška, et al., “Neurobiological View of Plants and Their Body Plan,” in Baluška, Mancuso, Volkmann, eds., Communication in Plants (New York: Springer, 2007).

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  1. Fichtner, et al., “Effects of Anthropogenic Disturbances on Soil Microbial Communities in Oak Forests Persist for More than 100 Years,” Soil Biology and Biochemistry 70 (March 2014): 79–87.

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E.-Detlef Schultz, coord., John Gash, Annette Freibauer, Sebastian Luyssaert, Philippe Ciaia, eds., CarboEurope-IP, An Assessment of the European Terrestrial Carbon Balance (Jena: carboeurope.org, 2009), ftp://ftp.bgc-jena.mpg.de/pub/outgoing/athuille/CE_booklet_final_packed/CE_booklet_Stand_02-03-09_screen.pdf, accessed January 30, 2016. 41. Markus Johann Mühlbauer, seminar, “Wetter und Klima” (“Weather and climate”), in “Klimageschichte” (“Climate history”), WS 2012/13, 10, Regensburg University. 42. A. Mihatsch, “Neue Studie: Bäume sind die besten Kohlendioxidspeicher” (“Trees are the best carbon dioxide storage units”), press release, 008/2004, Leipzig University, January 1, 2014. See also, Becky Oskin, “Old Trees Grow Faster than Young Ones, New Study Shows,” Huffpost Science, January 16, 2014, huffingtonpost.com/2014/01/16/big-trees-grow-faster-young_n_4609096.html, accessed February 10, 2016, and N.L. Stephenson, et al., “Rate of Tree Carbon Accumulation Increases Continuously with Tree Size,” Nature 507 (March 6, 2014): 90–93, nature.com/nature/journal/v507/n7490/full/nature12914.html, accessed February 10, 2016. 43. L. Zimmermann, et

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A.M. Makarieva and V.G. Gorshkov, “Biotic Pump of Atmospheric Moisture as Driver of the Hydrological Cycle on Land,” Hydrology and Earth System Sciences, 11(2) (2007): 1013–33, bioticregulation.ru/common/pdf/07e01s-hess_mg_.pdf, accessed February 16, 2016. 45. D. Adam, “Chemical Released by Trees Can Help Cool Planet, Scientists Find,” Guardian, October 31, 2008, theguardian.com/environment/2008/oct/31/forests-climatechange, accessed December 30, 2014. 46.

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  1. Sandra Ebeling, et al., “From a Traditional Medicine Plant to a Rational Drug: Understanding the Clinically Proven Wound Healing Efficacy of Birch Bark Extract,” PLoS One 9(1) (January 22, 2014): e86147, ncbi.nlm.nih.gov/pubmed/24465925, accessed February 16, 2016. 61. Michael G. Grant, “The Trembling Giant,” Discover, October 1993, discovermagazine.com/1993/oct/thetremblinggian285, accessed January 25, 2016. 62. G. Meister, Die Tanne (The Fir) (Bonn: Schutzgemeinschaft Deutscher Wald (SDW) [The German Association for the Protection of Forests and Woodlands], nd), sdw.de/cms/upload/pdf/Tanne_Faltblatt.pdf, accessed February 15, 2016. 63. Reiner Finkeldey and Hans H. Hattemer, “Genetische Variation in Wälder—wo stehen wir?” (“Genetic variation in forests—where are we?”), Forstarchiv 81 (July 2010): 123–28. 64. James K. Agee, Forest Fire Ecology of Pacific Northwest Forests (Washington D.C.: Island Press, 1993). 65. Frank Harmuth, et al., “Der sächsische Wald im Dienst der Allgemeinheit” (“The woods of Saxony in the service of the general public”) (Dresden: Staatsbetrieb Sachsenforst [State Forestry Commission of Saxony], 2003), 33, smul.sachsen.de/sbs/download/Der_saechsische_Wald.pdf, accessed February 15, 2016.

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  1. Jee-Yon Lee and Duk-Chul Lee, “Cardio and Pulmonary Benefits of Forest Walking versus City Walking in Elderly Women: A Randomized, Controlled, Open-Label Trial,” European Journal of Integrative Medicine 6 (2014): 5–11. 68. Wilhelmshaven Botanic Garden, “Wassertransport” (“Water transport”),

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