Top Quotes: “The Heartbeat of Trees: Embracing Our Ancient Bond with Forests and Nature” — Peter Wohlleben

“Conservation can be effective — that is to say, when we realize that what we are conserving is not just other forms of life but, first and foremost, ourselves.”

“All our senses are still intact. The only thing missing is a bit of practice — and here we can catch up.

Let’s first consider vision and ask a seemingly simple question: Why do we see trees in color?

We know we feel relaxed when we look at green trees. A shady green view even improves our health. But why do we see the color green in the first place? After all, this is not a skill most other mammals share with us. Their world is restricted to a narrow range of colors. Take the highly intelligent dolphin. Like many marine mammals, dolphins see the world in black and white, because their retinas contain just one type of cone (cones are cells that make it possible to see color). To distinguish between two colors, you need at least two different types of cones. Paradoxically, the one cone dolphins and other similar animals have is for the color green. This one cone allows them to distinguish between various levels of brightness, but that is all. Dolphins can’t even process blue light, which not only colors the surface of the ocean but also reaches way down into the depths.

OUR FOUR-LEGGED DOMESTIC companions, such as dogs and cats, and wild forest animals, such as deer or wild pigs, do considerably better than dolphins in the color department. In these mammals, the green cones are joined by blue cones, and this combination allows them to see a limited range of colors — although the various shades of red, yellow, and green all run together and look the same to them. Having both green and blue cones is still not enough, however, to be able to see the color green. To do that, you also need to have cones that are sensitive to red light — as humans and many other primates do. And so, even though the color green calms our minds and promotes healing processes in us, it plays no role in the lives of most mammals.”

“Why among mammals, have we humans developed this ability? Researchers suspect it has less to do with the color green and more to do with the color red. For example, many fruits found among the leaves of trees and bushes are red when ripe. We are not the only ones with our sights set on these. Many birds also have their eyes on them, and birds see red even better than we do. Plants have reacted to the situation: fruit that is eaten by mammals tends to be greenish-red when ripe, whereas fruit favored by birds is bright red.”

“Lazarus Geiger, an nineteenth-century German linguist, discovered that in many ancient languages there is no word for blue. Homer, an ancient Greek writer about whom we know very little, probably lived about eight hundred years before the birth of Christ. He described the color of the ocean as “wine-dark,” and texts from later centuries categorized blue as a shade of green. It was only with the development of and trade in blue fabric that the concept of “blue” was born. Since then, we have separated it out as a color in its own right and been consciously aware of it.”

“SO, DO WE see some colors only because there is a cultural reason to do so? Or, to put it another way, can we see blue only because we have a word to describe it? Jules Davidoff, professor of psychology at Goldsmiths, University of London, published the results of an impressive experiment on this subject. He and his team traveled to visit the Himba, a Namibian tribe that has no word for blue: On a computer monitor, he showed his test subjects twelve squares arranged in a circle. Eleven of the squares were green and the twelfth was very clearly blue. The Himba had great difficulty finding the blue square. Then he reversed the experiment. Davidoff showed people whose mother tongue was English another circle of twelve squares, this time all green. One of the squares had a tiny tinge of yellow in it that even I could not see. English speakers had considerable difficulty finding the square in question. Not the Himba, however. They might not have a word for blue, but they have many more words for green than we do. This means they can describe even the smallest variations of color in green, and this is clearly what makes it easier for them to immediately identify the slightly differently colored square in the experiment.”

“Science has recently discovered that near-sightedness is simply a case of our eyes adjusting well to seeing objects up close — think books and computers. The good news is that each of us can reverse, or at least put a stop to, this progression to near-sightedness. There is just one thing we need to do: go out into nature. As soon as our gaze drifts off into the distance, we are training our eyes to be farsighted.”

“Near-sightedness caught up with me, too. When I was sixteen, my prescription was -2.5. That meant that the world more than 12 feet (3 meters) away from me was a complete blur. But my eyes did not stay that way. Unlike most of my fellow sufferers, my readings constantly improved and, after a few years, they hovered between -1 and a reading just above the level at which you no longer need to wear glasses. Even back then, I made the connection between the change in my eyesight and what I did for a living. For my work, I spent a lot of the day out in the forest evaluating trunks and crowns in stands of trees that were to be thinned, and I did all of this from a distance.”

“THE NOSE, HOWEVER, is not the only organ we smell with. We also have olfactory receptors in our bronchial tubes, which expand when they detect certain scents. And even our small intestine gets involved in sniffing our food. Researchers at Ludwig Maximilian University of Munich have discovered that the mucous membranes of our gut contain olfactory receptors for thymol and eugenol, the substances that give thyme and cloves their distinctive scents. The receptors for these compounds were always thought to be only in the nose. When the gut detects them, it releases chemicals and changes the way it moves. The discovery is important because, in the natural world, we are exposed to a limited number of smells. The current flood of artificial compounds in perfumes, scented candles, and household cleaners can therefore cause intestinal discomfort and adversely affect our well-being.”

“WHEN SOME PEOPLE smell little or nothing out in the forest, they are not necessarily being inattentive. It could be that they have lost some or all of their ability to smell. And this is not unusual, as Dr. Sven Becker, a visiting researcher at the Ear, Nose, and Throat Clinic at the University of Munich, explained recently during a local radio program I was listening to. He estimated that 20 percent of the population in Germany has a compromised sense of smell, and 3 to 4 percent has lost this sense completely.”

“Just as the gut joins the nose in smelling things, it also joins the tongue in tasting things. It, too, contains sensors that were once thought to belong only in the nose. These cells are less easily tricked by sugary things than the cells in our palates. Normally, sugar, which the small intestine recognizes, triggers a release of hormones. Our consciousness registers this as a signal we are full. When we eat artificial sweeteners, however, this signal malfunctions and becomes weak and intermittent, which means our body craves more food.”

“The exciting part comes next. Will the person be able to find the tree now that he or she can see? Usually, it works astoundingly well and one thing quickly becomes clear: our hands translate what they feel into pictures.

IN 2014, A team of international scientists set up an experiment to see if there is a direct connection between touch and pictures — that is to say, our eyes. This is what they discovered: whenever the test subjects touched something with their fingers, their eyes stopped moving for a fraction of a second. We are not aware of these minuscule pauses, but clearly they are long enough to allow the brain to focus better and process what has been touched.”

“When he disturbed them with unpleasant noises, the subjects dramatically increased the rate at which they touched their faces. When the noises upset the rhythm of their brains and threatened to disrupt the subjects’ concentration, self-touch helped them get their brain waves back on track. To put it another way: self-soothing grounded their minds.”

“Some animals, for example, are able to sense electrical fields or volcanic eruptions before they happen. In the catastrophic tsunami that hit Southeast Asia in 2004, this was observed multiple times. For example, when panicked water buffalo raced inland, residents of the area saw the buffalo leaving and so also sought safety on higher ground, escaping the deadly wave.”

“As soon as a beech notices its crown is getting out of alignment, it grows specialized reinforcing wood to shore up one side of the trunk so it doesn’t bend any farther on that side. At the same time, it grows a different kind of wood on the opposite side that acts like the guylines on a tent to stop the trunk from leaning over any farther.”

“Medications such as antibiotics and, even more importantly, extreme hygiene mean that in many cases our bodies don’t have to deal with tiny attackers such as viruses, bacteria, or worms, and don’t have to break down the proteins they contain. But our immune systems must remain constantly on the alert — just in case. And because they mostly have nothing to do, they begin to turn their attention to less dangerous alien entities.

This is the reason the pollen of grasses and trees brings on such severe allergic reactions – after all, they are mostly made up of protein. In Germany, the concentration of pollen from birch trees, a species that is particularly likely to trigger an allergic reaction, is increasing year by year. There are a couple of reasons for this: not only do cities continue to plant birches despite warnings from medical professionals, but these trees also spread easily on their own.”

“If electrical impulses within the tree travel at a maximum speed of less than half an inch (1 centimeter) per second, and you make contact with the bark as you hug the tree, you could indeed get an answer right away. At least you could if the signal is processed at the point of contact, but that is something we do not know. Certain processes are regulated in the roots — how much water the leaves can use, for example — and the distance from the canopy to the roots and back to the canopy (or to your hands) varies from tree to tree, but it is a long way. And now we are approaching one of the central questions about what it is to be a tree. Trees store memories, respond to attacks, and transfer sugar solution, and perhaps even memories, to their offspring. All these abilities suggest that they must also have a brain. But no one has yet found any such thing.

Many parts of a living tree, like most parts of its trunk, are not even active anymore. With the exception of the outermost growth ring, none of the interior is still in use. You could even say it was dead. Nothing happens here apart from a few purely physical reactions, which are the same as the reactions you see in wood after a tree has been cut down. There’s the swelling and shrinking caused by getting wet or drying out, for example, as well as resistance to fungal decay thanks to tannins the tree stored earlier in its life that now act as a sort of waterproofing.

The vessels that transport water are found on the outermost growth rings. And that’s why it’s especially damp, even wet, there, which has the added advantage that most fungi can’t grow in these rings. Fungi like damp conditions, but (with a few exceptions) if they get too wet, they drown. And because many species of fungi like to make life difficult for trees, it’s a good idea for the tree to have a zone running around the outer part of its trunk that repels most attackers. But, let’s get back to the brain. Even in the outer parts of the trunk, most of the cells are dead wood.”

“Baluska and his colleagues sedated plants that feature moving parts, such as Venus flytraps. These plants catch their prey in a trap that snaps shut as soon as insects touch trigger hairs on the inner side of their double-lobed leaves. The two sides of the leaf fold together in a flash, capturing the insect between them, and the plant then digests its prey. The anesthetics the scientists used, which included some that are used on people, deactivated electric activity in the plants so that the traps no longer reacted when they were touched. Sedated peas showed similar changes in behavior. Their tendrils, which usually move in all directions as they slowly feel their way through their surroundings to find supporting structures to grow on, stopped searching and started to spiral on the spot. After the plants broke the narcotics down, they resumed their normal behavior.

Did the plants wake up as we do when we come to after a general anesthetic? This is the critical question, because in order to wake up, you need one thing above all others: consciousness.”

“Dead trees fell over, sank into swamps, and gradually formed coal.”

“So much carbon dioxide was removed from the air and so much oxygen was added that insects became larger than they had ever been before. The size insects can grow to is limited by the way they breathe. Oxygen is distributed through their bodies not by arteries and a circulatory system with a pump (the heart), but via a system of tiny tubes that delivers it directly to the cells. The longer these breathing tubes are, the less efficient they become, which means if insects are too large, they can’t get enough oxygen. Based on the current levels of oxygen in the air, the largest insects can grow is about 6.5 inches (17 centimeters), and in the conditions we have today, no insects can grow any bigger than this. Three hundred million years ago, however, trees were producing so much oxygen that the levels in the air were considerably higher than they are today. Instead of 21 percent, it was at 35 percent — and that meant insects could grow considerably larger, which is exactly what they did. Dragonflies with wingspans of 27 inches (70 centimeters) or more patrolled the skies and centipedes nearly 10 feet (3 meters) long scurried through the leaf litter on the ground.”

“A case in point is the bog orchid, which grows in the cool northern woods of North America with subspecies in Scandinavia and Russia. These orchids are on the lookout for pollinators for their white blooms, but in the swampy landscapes of the North there are few bees around. What there are in droves, as every vacationer can painfully attest, are mosquitoes. But these insects are not well known for their love of flowers. We have them pegged as nothing but annoying bloodsuckers.

And here is where the bog orchid comes in. It imitates the scent of humans to signal to mosquitoes that there might be a meal available. In search of victims, the insects happen upon the flowers and unintentionally pollinate them. But they don’t fly away completely un-rewarded. Even female mosquitoes drink more than just blood. Every once in a while, they enjoy a few carbohydrates on the side, which they get from a little sip of nectar.”

“Even our closest relatives, chimpanzees, cannot start fires and, indeed, are clearly afraid of them. It is the ability to start fire that sets us apart from other species.

Just when the first flames were intentionally ignited is lost in the mists of time, However, a discovery in the Wonderwerk Cave in South Africa leaves no doubt that 1.7 million years ago humans were sitting around a fire they had made themselves.”

“Smoke has an evolutionary impact. Then, as now, it was responsible for premature deaths, and over the course of hundreds of thousands of years it should have left a genetic imprint. And, indeed, it has. Perdew and his colleagues discovered a gene segment that distinguishes us from Neanderthals and Denisovans: the so-called Ah receptor. It inhibits the destructive effects of environmental pollutants, including those contained in smoke. Depending on the molecule, this receptor reduces toxicity for modern humans by a factor of one thousand.

What was the situation with Neanderthals? After all, the Neanderthal brain also benefited from food that was thoroughly broken down and made more digestible by fire. It was in some respects even larger than the brain of modern humans. But perhaps because of their smoky homes, Neanderthals didn’t live as long as Homo sapiens. And it could be why, one day, they died out completely. At least that’s what some researchers think, although these early humans probably developed other mechanisms to cope with fire and smoke.”

“The deciduous forests native to Germany hardly ever catch fire from natural causes; the coniferous forests of northern Europe, in contrast, do catch fire more easily. The trunks, needles, and bark of conifers are full of resin and other flammable substances. In dry summers, these trees are like gas tanks waiting to explode. But what tree likes to burn? Intact coniferous forests store a great deal of water in mosses, lichens, dead wood, and humus. All those soggy materials inhibit fire. Moreover, the lightning strikes that are the leading natural cause of forest fires are usually accompanied by heavy rains that extinguish the fires just as they are beginning to burn. When a fire starts in dry weather, it almost always was and almost always is human caused.”

“The ionosphere, a layer that begins 50 miles (80 kilometers) above the ground, is positively charged, whereas the surface of the Earth is negatively charged. The difference between the two is more than 200,000 volts. The differential increases the farther you are above the ground, and it does so quite rapidly. The difference in the first few feet above the ground in good weather is from 100 to 300 volts — every 3 feet (1 meter). Under a thundercloud, the difference can be as much as thousands of volts per meter.

Despite this, you don’t have a higher voltage around your head than you do around your feet, because your body is an efficient conductor of electricity. At some time in your life, you have probably felt a brief shock as you touched a car or a piece of plastic garden furniture. What’s happening here is that your body is equalizing the voltage between the object you just made contact with and the ground. This way, you remain unelectrified and still have the same amount of voltage in you as the ground.”

“Fish, for example, have a so-called lateral line organ in their skin that detects the Earth’s magnetic field. The fish use this as a navigational aid, but that is not all. Sharks use differences in charges to identify prey. Just a few nano-volts – that is a billionth of a volt – is sufficient. (Remember, the difference at the branch tips of an oak tree can amount to many thousands of volts.)”

“NOW ITS OUR turn. Why should we feel electric charges or, to put it the other way around, why shouldn’t we? After all, our bodies are entities controlled by electric stimuli, and electricity flows through them constantly. Every piece of information that travels through our nervous systems, every thought that arises in our brains, is passed on by pulses of electricity, even though the amount of electricity involved – about a tenth of a volt-is minimal. That means, however, that we must be extremely sensitive to stronger currents, because a system designed for weak currents has to be easily disrupted using stronger ones. And with that we find ourselves in the middle of the disputed field of “electronic smog.”

By now, it is beyond dispute that our body reacts to electric fields.”

“Electromagnetic radiation is also the reason people are worried about using cell phones. After all, you have to hold the phone up to your ear and, while it’s there, it has to send out a signal that is strong enough to reach the nearest broadcast antenna. That is why the Federal Office for Radiation Protection here in Germany, which tends to be conservative in its judgments, recommends that you use a landline for calls if one is available. It also recommends keeping conversations on your cell phone as short as possible or texting instead – that way you don’t need to hold the phone anywhere near your brain. To me, all this sounds less than reassuring, especially as the suggestions don’t address the impact of electromagnetic radiation on the nervous system: the basis for the limits is the warming of the adjacent tissue, a reaction more akin to how a microwave works. So, just to be clear, the question here is whether the transmissions from your cell phone are powerful enough to cook your brain or heat it up enough to damage it.

At the moment, there is nothing official to suggest these transmissions cause cancer, but clearly some important questions have been overlooked. If a system as finely tuned as our neural network works using weak electric signals, how might our internal data transmissions be affected by officially sanctioned gadgets (cell phones and the like) that create electric fields so strong that they heat up our brains?”

“Your hair stands up on end when it is electrically charged because (unless it is really greasy or wet) it is a poor conductor of electricity. Therefore, you are grounded, but your hair isn’t necessarily.”

“Might the tree be aware of your touch in some other way? There is one strong contender here — with young trees, at least — and this is a process known as thigmomorphogenesis, which is when plants grow more slowly after being touched. All you have to do, for example, is stroke your tomato plants for a few minutes each day and they slow their upward growth and put their energy into growing thicker stems instead.

This, however, is not the plant saying it loves you, too, but rather the plant reacting to what it likely experiences as a breeze blowing by, because the wind elicits a similar response. The shorter the plant, the less leverage the wind gets and the less pressure there is on the plant’s roots, so a tomato plant with a shorter, thicker stem is more stable. The same is true, of course, for movement caused when animals brush past plants — plants that are less stable are more likely to fall over. Therefore, it may well be that the way tomatoes or small trees respond to this kind of disturbance (not only from the wind) is part of their genetic repertoire.

If you’ve noticed that plants are healthier after you’ve stroked them, you’re right. Scientists have discovered that plants stimulated by touch produce more jasmonic acid. This acid not only regulates height and triggers the growth of thicker sterns so the plants are more stable, it also makes the plants more resistant to pests.”

“IF YOU WERE hoping to hug a tree and get a hug back, this information must be disappointing. The responses I have described are simply a defensive strategy plants employ against external events they view as a threat. Moreover, if the tree is to experience your hug, it must be sensitive enough to touch that it can feel your arms around its trunk. A tree does indeed possess a certain sensitivity to touch, but in completely different circumstances. For example, if a neighboring tree or a metal post presses against its trunk, it will begin to grow around the obstacle. For this to happen, however, the pressure has to be strong and above all persistent over time — two conditions that are not met in a hug. Large trees in particular have thick bark as befits their stature, and nearly all the cells in the outer layers are dead, which means trees feel as much, or as little, with their bark as we feel with our hair.

We do, however, find a great deal of sensitivity in a completely different part of the tree: its roots. At this level, the tree works its way through the ground with its root tips, which contain brain-like structures. The root tips feel, taste, test, and decide where and how far the roots will travel. If there is a stone in the way, the sensitive tips notice and choose a different route. The sensitivity to touch that tree lovers are seeking is therefore to be found not in the trunk but underground. If it is possible to make contact, the roots would be the first place to try. They have the additional advantage that they are easy to reach and, in contrast to the upper parts of the tree, are active even in winter. However, they like neither pressure nor fresh air — and so there’s no point exposing these tender structures because even ten minutes in the sun spells death for their tissue.”

“Dr. András Zlinszky at the Balaton Limnological Institute in Tihany, Hungary, is shedding some light on the matter. Some years ago, he and colleagues from Finland and Austria noticed that birch trees appear to rest at night. The scientists used lasers to measure trees on calm nights. They noticed the branches hung up to 4 inches (10 centimeters) lower, returning to their normal position when the sun rose. The researchers started talking about sleep behavior in trees. Clearly, Zlinszky could not get this discovery out of his head, and he decided he needed to investigate further. He and a colleague, Professor Anders Barfod, measured another twenty-two trees of different species. Once again, they documented the rise and fall of the branches, but this time some of the cycles were different. The branches changed position not only morning and night, but also every three to four hours. What could be the reason for this rhythm?

The scientists turned their attention to water transport. Was it conceivable that the trees were making pumping movements at these regular intervals? After all, other researchers had already determined that the diameter of a tree’s trunk sometimes shrinks by about 0.002 inches (0.05 millimeters) before expanding again. Were the scientists on the trail of a heartbeat that used contractions to pump water gradually upward? A heartbeat so slow that no one had noticed it before?”

“Researchers put caterpillars on samples of Arabidopsis. The vibrations caused by the caterpillars munching were enough to shake the plants’ stems, and the researchers used laser beams to record the vibrations. When researchers then played these vibrations to plants that were not being eaten, they produced particularly large quantities of defensive chemicals when they were later attacked. Wind and other sounds with the same frequency did not elicit a reaction from the plants.

Arabidopsis, then, can hear, and this makes perfect sense. Thanks to acoustic warnings, it is able to recognize danger some distance away, so it can make appropriate preparations to defend itself. What is particularly important here is that the plants ignore noises that pose no threat to them. These noises probably include human voices as well as different styles of music. What a shame. The reports of crops that can clearly distinguish classical music from rock music sound so delightful.”

“According to the docent who was leading the tour, the lake was emptied and cleaned every once in a while, revealing tons of fish. But where on earth had they come from? The answer is quite simple: their eggs had traveled tucked in the feathers of ducks that discovered the lake and decided to stay a while, offloading the stowaways.”

“The mighty chestnuts that dominated eastern forests were wiped out by a fungus that arrived from Asia a century ago. American chestnuts had survived for millions of years and were destroyed in forty. The trees die back to the ground. They can put up shoots, but the new growth soon dies back again. Today, scientists are trying to restore American chestnuts by breeding crosses between American chestnuts and Chinese chestnuts that are immune to the fungus. Interestingly enough, this is possible because more than 60 million years ago, Asia and North America were joined together in a super-continent and so many of the trees growing on these two continents today originally grew together. After the continents split apart, the trees on the separated landmasses took their own evolutionary paths.”

“Remnant rituals from age-old forms of tree worship are practiced to this day. Take the southern Italian region of Basilicata. There is a form of tree worship there that must be thousands of years old, at least, and possibly dates back to the Stone Age. Although it was outlawed around the year 725 CE, it continued to be practiced and became integrated into rapidly spreading Christian rituals. At its center stands the marriage of trees. It is not a marriage in the traditional sense, because after a complicated ceremony, the trees are cut down. On the Sunday after Easter, a troop of people well versed in the rituals marches out into the woods to find the bridegroom. He must be an oak that has grown tall and straight. That day, the tree is merely flagged. A week later, people go looking elsewhere for the bride. She must be an evergreen, so a conifer or perhaps a holly. Her beauty is judged by her splendid, evenly proportioned crown. The trees breathe their last on Ascension Day, because that is the day they are both cut down. Oxen pull the trees into the village, where they are married on the holy day of the Pentecost. The ceremony involves attaching the crown of the holly to the trunk of the oak so they look like a single tree. Everything happens slowly, according to strict rules, with the lively participation of the local population (and today sometimes tourists, as well).”

OTHER REGIONS HAVE the same kinds of rituals with similar roots. In many places, a May tree is put on display. Sometimes more than one. Where I live in the Eifel and throughout the area around Bonn, there are hundreds of them. The recipients of these trees are young women whose admirers head off into the forest the night before the first of May. There they steal a tree. The less bold among them buy their trees from foresters or local youth groups, which use the sale of trees as a fundraising activity. Those who do not pay find their prizes secretly carried off in the early hours of the morning by members of these groups. The only suitable tree in this region is the birch, which has often not yet leafed out because the weather is still so cold. They are decorated with garlands of crepe paper and then carried to the loved one’s home — although today this often means driving them over in the open trunk of a car.”

““Of course a plant, trees can feel pain, the professor answered when I asked him about it. “Every life-form must be able to do that in order to react appropriately.” He explained that there is evidence for this at the molecular level. Like animals, plants produce substances that suppress pain. He doesn’t see why that would be necessary if there was no pain.

Baluska was ready with other quite different discoveries, as well. There’s a vine that grows in South America that adapts to the form of the tree or bush it is climbing on. Its leaves look just like the leaves on the host plant. You might think this is chemically controlled. In that case, the vine might be detecting scent compounds from the bush and changing the shape of its leaves in a way that was genetically predetermined. Three different leaf shapes had been observed. Then a researcher came up with the idea of creating an artificial plant with plastic leaves and relocating our botanical chameleon to its new home. What happened next was amazing. The vine imitated the artificial leaves, just as it had imitated the leaves in nature. For Baluska this is clear proof that the vine can see. How else could it get information about a shape it had never encountered before? In this case, the usual suspects – chemical messages released by the host plant or electric signals between both plants — were absent. He went further. In his opinion, it is conceivable that all plants might be able to see.

Up until then, the only thing I knew was that trees can differentiate between light and dark. Sleep behavior has been researched in birches and oaks, and beeches can measure day length — all of this requires light receptors that transmit signals to the trees and spur the whole organism into action. This is far removed, though, from vision in the sense of being able to recognize shapes and colors. And now this: plants which register precisely that and change their behavior accordingly. I found that astonishing.

Baluska directed me to research being done on the cuticle or outer layer of leaves. On most plants, this layer is completely transparent, which makes no sense if all the leaves are doing is collecting light to manufacture sugar. In that case, these outer cells should be equipped with green chloroplasts, the organs used for photosynthesis — after all, this is where the most sunlight falls. Logically, less light is harvested in layers farther from the surface. And yet the cuticle is transparent, which seems wasteful. Not only that. In several plants, the cuticle is constructed in the shape of a lens, which means that it focuses light, making the cuticle functionally similar to the lens in our eye. It doesn’t seem logical to me to focus light if photosynthesis is the only goal, because the cuticle could simply let the sun’s rays through. Focusing light doesn’t increase how much light falls on a leaf. The same amount of light is simply more concentrated or, more specifically, focused more intensely to the back of the cell.”

“LEAVES THAT FUNCTION like eyes? There’s an idea that takes some getting used to, particularly as a tree regularly discards its “eyes” in the autumn when its leaves fall off. Does that make leaves disposable eyes? In a certain sense, yes. A working life of six months (under European climate conditions) is relatively long in comparison with some animals. Flies, for example, use their eyes for little more than a month simply because that’s how long they live. And mayflies, which live for barely a day after metamorphosing from a larva into a flying insect, use their visual apparatus for less than twenty-four hours and yet the eyes they have are real.

There’s another thing with trees. The cells in the leaves, once they are formed, last for the whole growing season, which means they are relatively long lived. In contrast, our eyes are in a constant state of partial rejuvenation: the cells in the outer cornea, for instance, are completely replaced every seven days.”

“If you trace its origin, you come to the Brothers Grimm of fairy tale fame. In a dictionary of the German language that they published in 1860, they mention that old German characters were scratched onto wooden boards. And because these boards often came from beech trees (Buche in German, which is pronounced “boo-huh” in English), the name for such writing tablets was transferred from the tree to the functional object — Buch, the book.

But the term could possibly have arisen much earlier, when runes were carved into wooden sticks made of beech. In German, where letters are Buchstaben (Buch — beech and Stab — stick), this gets us one level deeper, for with Buchstaben, it is much easier to see the origin of the word.”

“Aspen leaves have stalks that allow them to twist in the lightest breeze. This might allow them to gather more light so they can produce more sugar.”

“In the middle of the eighth century, Central Europe was still 90 percent forested and all the forest was primeval. There was no form of forestry at that time because it was not necessary. Population density was low and forests seemed practically endless. Areas for agriculture, in contrast, were in short supply, and it took a great deal of effort to wrest them from the clutches of nature. Not only were the trees in the way, so were their roots. Each and every one had to be dug out and dragged away by teams of oxen. Without this preparation, plows would have gotten stuck every few yards. It’s little wonder our ancestors decided to use place names to memorialize their laborious clearing of the land.

Some of the place names even reflected the clearing method used. In the German-speaking Alps, if trees were simply felled and burned, leaving the roots, schwenden (which means “slash and burn”) might be part of the name. This quicker method was not suitable if you wanted to plant crops, but it was fine if you were not going to plow the land and all you needed was a pasture for livestock. Schwenden (the past participle of which is schwand) appears either as a place name in its own right (as it does in Baden-Württemberg and Bavaria, both of which have towns called Schwenden) or as part of the name (as it does in settlements such as Herrenschwand or Untergschwandt). Other variations can be found in city names such as Bayreuth. Reuth is another term for Rodung, and Bayreuth means a clearing in Bavaria or a clearing made by Bavarian people. Then there is Stockum, where the name tips its hat to the tree stumps (Stock) that remain after the trees have been felled. In the British Isles, names ending in -lea, -ley, -leigh, or -leah indicate forest clearings, and -thwaite indicates a forest cleared for tilling, often with a dwelling on it.”

“The compounds beeches, oaks, and many other trees release into the air to communicate among themselves affect our circulatory system and our subconscious, and our blood pressure sinks — although not in every forest. Experiments at the end of the 1970s discovered that while native deciduous trees in Germany show positive effects, our blood pressure can rise in non-native spruce or pine plantations, where stressed conifers exchange chemical messages about insect attacks and lack of water — and we likely pick up on these even though we are not consciously aware of them. Your subconscious translates this arboreal activity into changes in your body as well as in your mind.”

“A walk in the woods does more for your immune system than you might think: it benefits from the defensive strategies of the trees.

Way back in 1956, the Leningrad biologist Professor Boris Tokin demonstrated that conifers did a good job disinfecting their surroundings. He discovered that the air around stands of young pines was almost germ-free. The cause of this clean air was the trees themselves, which were giving off phytoncides, a kind of plant antibiotic.

Why do conifers do this? The answer is that they are constantly being attacked by an enemy we cannot see, one that drifts in the breeze. Every 35 cubic feet (1 cubic meter) of air carries up to ten thousand fungal spores just waiting for their chance to land on a broken branch or damaged bark.From there, the fungus grows into the tree and slowly eats it from the inside out. The wood rots and the tree dies. It’s understandable that many conifers want to defend themselves at the earliest possible opportunity, preferring to take out the attackers before they even land. (Deciduous trees deal differently with fungus.)

Conifers fight fungal spores before they reach their bark, and people who suffer from allergies benefit from the trees’ preventative measures. But people who suffer from allergies are not the only beneficiaries. Unbeknownst to you, you breathe in the trees’ defensive compounds, the phytoncides, with every breath you take, and they help protect your body, too. In your case; they trigger a reaction that reduces inflammation. In addition, phytoncides have been found to reduce the activity of cancer cells. Japanese researchers at the Nippon Medical School discovered this when they sent test subjects out into the forest or the city. Cancer-killing cells and anti-cancer proteins increased in those people who visited the forest but not in those who visited the city, and the elevated concentrations of both could be detected in the participants’ blood up to seven days after the forest walk.

Researchers in Korea ran similar experiments to test this phenomenon. They had a group of older women walk in the woods and another group walk in the city. The results were astounding. The blood pressure, lung capacity, and elasticity of the arteries of the forest group improved, but there were no measurable changes in the city group.

THE TERM “city” is perhaps a bit vague when it comes to health. Apart from noise and air pollution, there are other biological characteristics that differ considerably from suburb to suburb. This brings us back once again to trees. Various studies ascribe clear health benefits even to street trees. In a large-scale study, scientists at the University of Chicago discovered that a single tree by the front door improves health and well-being. They gathered data from about thirty thousand residents of Toronto — and from 530,000 trees the city had already mapped. The result: ten more trees in a residential neighborhood improved the health of the residents as much as an increase in income of $10,000 a year (including the improved medical care that comes with such an increase). And we are not only talking about mental health. The likelihood of heart and circulatory diseases, the leading cause of death in North America these days, dropped measurably. Eleven more trees in the neighborhood was an improvement in cardio-metabolic health equivalent to an additional $20,000 a year or, measured another way, it reduced a person’s biological age by 1.4 years.”

“In order to spare the ancient beech woods, I established one of the first forest burial grounds in Germany, where you can choose a tree under which you will later be laid to rest. Apart from getting a maintenance-free grave, you will also be ensuring that the old deciduous forest will not be cut down for at least another ninety-nine years, which is the length of the lease on the burial plot. In addition, I launched an ancient forest program where additional areas of ancient beech forest could be leased by the square foot with a click of the mouse. My goal was to save as many of the last ancient deciduous forests as I could in the place where I lived.”

“You can, for example, eat the leaves of beech, oak, and many other deciduous trees with no worries at all. They’re even good for you. But when I try to get my guests excited about trying them, they just look at me. You mean you can just bite into a leaf? Really? Yes, you can, and in spring, at least, right after the trees have leafed out, the delicate green leaves taste delicious and slightly bitter. You can concoct beautiful salads using only beech and oak leaves.

You don’t even need to bring any headache medication into the woods, because willows offer you something similar. Their bark contains salicin. Willow is Salix in Latin, so salicin is named after the tree. Depending on the species, willow bark contains up to 10 percent of this substance, which your body processes into salicylic acid after you have ingested it. The well-known synthetic medicines whose active ingredient is acetylsalicylic acid are more potent, but they also have more side effects, such as acting as a blood thinner. If you have a headache or a fever and you don’t want to experience these side effects, you can reach for a cup of willow-bark tea instead. People have been doing that for thousands of years, as we know from clay tablets dating back to 700 BCE. Synthetic salicylic acid dates back to research done around 1830, when scientists figured out the secrets of willow-bark tea. The modern white tablets are nothing more than a chemical reconstruction of compounds present in our native trees. Of course, it would be a shame if you were to go out into the forest right now and peel the bark off a willow. That would be like peeling the skin off a living animal. But if you cut off a couple of twigs and take the bark off them when you get home, you will minimize the damage to the tree.”

“The forest is helpful not just when you have a headache. How about something to treat insect bites and other swellings? For this you need a maple or, to be precise, one of its leaves. Lightly crush the leaf and lay it on the insect bite, and it will help keep the swelling down. This also works on your feet if they’ve swollen after a long hike.

Oaks, on the other hand, are most useful internally. For instance, if you have a sore throat. You need some bark, which you brew into a tea, and then sip. Now, as with the willow, I don’t want to encourage you to peel the bark off oaks, because that would severely damage the tree. If trees have been cut in a wood near you recently, you might pry some bark from a downed trunk. A trip to the drug store or health-food store is even easier. There you will find oak bark tea already dried and packaged.”

“You can give them a special treat, for instance, by making chewing gum. All you need is a dear, thick, stone-hard drop of resin from a spruce. You can identify spruce by its reddish-brown bark and long, hanging cones. Don’t worry, the resin from pines, Douglas firs, firs, or larches is not poisonous, chewing gum just works particularly well with spruce resin.

Put a solidified drop of spruce resin in your mouth to warm it up to body temperature. Test it carefully every once in a while to see if it’s soft yet. Don’t bite down on it too hard. If you do, the resin will shatter into a thousand pieces and immediately release all its bitter compounds. So, take your time and gradually begin to chew. Spit the bitter compounds out when you taste them (now you know why you should undertake this activity only when you’re out in the woods) until finally you have a chewable, rosy-colored mass — it’s ready. The tastiness of this gum is debatable, as it never loses its resinous undertone, so I suggest you consider this activity primarily as a star turn during a walk if you’re the trip leader and want to offer your family or group of friends something different.

Trees, incidentally, even offer something for the kitchen. Douglas-fir needles taste tart and bitter, a bit like candied orange peel, and are great for flavoring a wide variety of dishes.”

“Chimpanzees, for example, have been seen eating the pith of bitter leaves as a purgative to rid themselves of gut parasites. But how did the researchers know the apes were eating the plants for their medicinal properties rather than for their calories? That was easy, because the leaves are toxic, even for chimpanzees. The animals seemed to know exactly how much they could eat safely, and after a purge they didn’t eat these plants until the parasite loads in their guts increased once again. The animals obviously had a pretty good idea of what they were doing.

You can picture apes self-medicating from nature’s drugstore, but what about animals that are not as closely related to us? Take, for example, birds. To rid themselves of parasites, they not only use plants but also the services of other animals. Ants become their unwitting assistants when it’s time to remove mites and other pests. To enlist the ants’ help, the birds crouch down over one of the mounds made by these social insects and fluff out their feathers. The ants defend themselves against what they assume is an animal attacking their home by biting anything they cannot identify and, what’s most important for the bird, spraying caustic acid. Between these two defensive measures, the ants kill large numbers of the parasites tucked away in the bird’s feathers.”

“Cinnabar moth caterpillars, however, exploit ragwort’s extreme toxicity. Although they eat other plants, they are irresistibly drawn to the toxic substances in ragwort. The alkaloids do not harm them. Instead, they spread through the larvae’s tissues, making the caterpiliars themselves deadly poisonous. That is their defense against anything that wants to eat them. And so that would-be attackers are aware of the danger, they adorn themselves with the same warning colors used by yellowjackets: alternating rings of black and yellow.

Although the cinnabar moth caterpillar is guided by instinct, the house sparrow provides good evidence that it purposefully uses substances in its surroundings as medicine. Dr. Monserrat Suárez-Rodriguez and her team from the National Autonomous University of Mexico were researching sparrow nests. They discovered that many of the birds incorporated cellulose from cigarette butts in their nests. There was an appreciable amount of nicotine in this material, which helped to significantly reduce the number of mites in the nest. Because in this case the sparrows were not using plants — that is to say, natural medicine — this points to purposeful behavior.”

“What this means is that if you own one or more trees, you are liable for any damage they cause. It’s much like owning a dog — it’s a good idea to have liability insurance. The same principle applies to trees on your property.

Nervousness about potential property damage or, in the worst-case scenario, loss of life often leads people to err on the safe side and remove trees, especially in Germany where you are guilty of a criminal offense if a tree on your property strikes and kills someone.”

“Id like to put all this in the context of the population of Germany. Let’s assume twenty deaths a year — which is on the high side according to news reports about such events — and an average age of forty for the people who are injured or killed. I’ll calculate this as a percentage of the total population. Assuming a life expectancy of eighty, dangerous trees would reduce this by 0.00001 percent. The presence of trees in the city, on the other hand, raises this life expectancy by 1.8 percent. That is 180,000 times more. Even if slightly fewer trees were “cleaned up,” which would reduce the gap between the numbers, there is still a huge difference between them. This calls into question the radical removal of supposedly dangerous trees. I am emphasizing this because traffic safety measures recently, here in Germany at least, are bordering on the fanatical.”

“When animals hear people making noise, instead of getting stressed, they relax, because they realize right away that noisy people have no intention of hunting them.”

“In Germany, if you cut down a tree without a permit, you can be slapped with a fine of up to €50,000 (which is about US$55,000 at today’s exchange rate), and many cities in North America have tree ordinances.”

“Paper has the environmental advantage that it can be recycled without leaving residues, as long as it is print-free. But how many bags out there are free of business logos or synthetic materials?”

“SO, WHAT IS the alternative? It has to be this: less packaging. We had a similar movement in Germany back in the 1970s and ‘80s when the slogan was “burlap instead of plastic.” Until the mid-1990s, multiuse containers were widely available. You brought them with you and filled them with milk, processed meats, and cheese. I still remember campaigns at school where we spent years collecting the foil lids of yogurt containers. After all, they were made from valuable aluminum that was energy intensive to mine and process.”

“Given the massive aluminum rims sported, it seems, by every second car these days or the number of aluminum wheels on bicycles, such efforts from the past seem quaint and not particularly effective. And they didn’t last very long.”

“We all know evaporation cools things down. We benefit from this when we sweat in summer to ensure our body temperature doesn’t rise too high. And forests do the same thing. Forests transpire enormous amounts of water — up to 130 gallons (500 liters) for a single beech on a hot summer’s day. Transpiration reduces the temperature in the forest by many degrees, and you can feel this. It’s not just the shade that causes the distinct difference when you walk from an open area into a forest; it’s something the trees are actively doing.

Most species of trees don’t like it hot; they prefer moist, cool conditions. At least, that’s the case for trees in the temperate regions of northern latitudes, which is where the largest forests on Earth grow. When forests are cool and moist, less water evaporates from the ground and, in these conditions, trees photosynthesize quickly and efficiently. The well-known German meteorologist and television weather forecaster Sven Plöger once told me how aware he was of this effect. Temperatures would climb steeply in April as the sun rose higher in the sky, only to cool down again in May. Temperatures dropped as the trees unfurled their leaves and the new growth immediately began transpiring. It’s amazing that the effect is so noticeable given that here in Germany only 12 percent of the original forest cover remains. And the remaining trees are not ancient trees, which are the ones that cool things down most effectively, but overwhelmingly extremely young commercial forests that don’t manage water well. The residual cooling effect is nonetheless impressive and surely only a glimmer of what it once was and could be in the future.”

“All the carbon? Didn’t I just explain how most of the dead wood left in the forest remains permanently in the ground in the form of humus? That is indeed the case, but it holds true only for ancient forests where an old tree dies every once in a while. The death of one tree doesn’t change the microclimate, and the forest remains shady and cool.

Things are very different when it comes to clear-cuts or clearings created by storms. In these areas, the sun beats down mercilessly, which kicks fungi and bacteria into high gear. They break down all organic substances completely and make sure every last fragment of wood ends up back in the atmosphere as carbon dioxide.”

“In an international study, a team led by Dr. Kim Naudts from the Max Planck Institute for Meteorology discovered that the changes brought about by forestry practices in Europe over the last three hundred years have contributed to a rise in summer temperatures of more than 0.22° (0.12°C), despite the industry’s massive tree-planting programs.

That might not sound like very much to you, but think about the vigorous debates going on today about whether the warming of the climate should be restricted to 2.7° or 3.6° (1.5° or 2°C), even though the difference seems tiny. The number after the decimal point is extremely important, as the following example shows. If we assume an average rise in global temperatures of 2.7° (1.5°C) — a level we will surely reach soon — then 0.22% (0.12°C) is 8 percent of that total rise. That is larger than the contribution to total global greenhouse gas emissions made by a country such as India.”