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The forests of planet Earth: a celebration of diversity. What we refer to as woodland nowadays is often man-made commercial forest. Yet, the forests can be so much more. In various climate zones, it overcomes significant challenges in surprising and fascinating ways. From the northern forests of the Arctic Circle to tropical jungles, from coastal forests steeped in salt water to the forests of the rugged mountain slopes, these are the forests of our planet.
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The forest is like a living organism, ancient and full of hidden networks. Vegetation needs water and specific temperatures. Despite the challenges, however, it manages to survive in the most varied locations on Earth. How does it manage to adapt, even in adverse conditions?
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Coexistence in the woods is a symbiosis. The trees depend on the animals, and many animals depend on the trees.
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The great significance of the forest has always led humankind to mystify it. The northern forest of Scandinavia: for seven months a year, the temperatures are below freezing here, yet the trees survive. It seems like the cold doesn't affect the forest much, for good reason. As one approaches the poles, the animals of a species become larger; in warmer regions, they're smaller. Like moose, for example: in northern Sweden, they're noticeably bigger than in the south.
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It's a simple trick.
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The larger the volume of an animal in relation to its body surface, the more warmth it can conserve. Volume saves warmth, while surface area releases it. With trees, however, things are different. Thick trunks would, of course, be better suited to conserving body warmth, but trees don't produce warmth and are therefore dependent on air temperature.
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Besides, their growth actually uses up valuable energy and time, both of which are in short supply. The polar summer, when they can grow, is short, and the time when they are free of frost is also restricted. But this is when they must produce high-energy sugar solution from water. They have to economize on their energy, as well as growing and reproducing within the shortest time period. That's why trees get smaller and smaller the further north they appear. Winter temperatures impose a natural boundary on the forest: the tree line. Water is only available here for five months a year in liquid form, but woodland still thrives. The trees can only survive thanks to a kind of hibernation. The trunks are filled with veins; some of them carry sugar solution from the leaves to the roots, others supply the leaves and needles with water from the roots upwards. The energy-rich sugar allows the tree to grow. When it gets too cold, deciduous trees shed their leaves. They do not require any more water to produce sugar solution. The tree ceases to supply water, and the stream of sugar solution is halted, acting like protective anti-freeze. In addition, the tree is insulated by an air cushion between the trunk and the outer bark. Unless the sun comes out, while on the sunny side the cells of the tree warm up and begin to expand, the shaded side remains frozen stiff. Pressure builds in the trunk, finally becoming too much. The crack is a gateway for diseases and fungus. Not every tree can survive such damage. As long as snow is lying on the treetops, they're guarded against rupture. It acts as insulation against wind and extreme cold. In the hollows beneath the snow layer, temperatures can even climb above zero. Abandoned by the plants, animals are left to scavenge as best they can. In winter, red deer search out the last patches of grass. If the snow cover is too high, they're left with only bark. This is not substantial enough, and the animals' health suffers. Those who can find lichen are better off. Reindeer have adapted and so are able to gather high-energy food like this. Further east, in Siberia, a puzzling creature lives from lichen, even if its teeth look more suitable for other diets: musk deer. Their sharp canine teeth serve more as defensive weapons. Forest dwellers have to possess special talents in order to survive. The capercaillie has resorted to eating entire fir tree shoots. Its thick plumage protects it from the cold. One pound of fir sprigs a day is enough for it to get by. Deciduous trees become fewer the further north the northern forest reaches, or the higher up the mountain forest stretches. The last trees left are mostly coniferous. This is because the cold persists longer in these areas. But it's not the low temperatures that challenge the trees; rather, the lack of moisture. Water only exists in the form of snow and ice. Even the water in the ground is frozen and therefore unattainable for the trees, as the roots cannot take it up. That's a major problem for deciduous trees. Water is constantly evaporating through the thin leaves that are mostly dried out by the wind, which is why they shed their foliage when it gets too cold. In some polar regions and areas of high altitude, the warm periods are so short that it's not worth forming leaves; too little energy would be left over to grow and maintain a large tree. In order to survive here, the forest needs a strategy: needle-like leaves. They lose next to no water in the wind, as their surface area is smaller and their skin thicker. Some species also offer extra protection for their needles with a layer of wax. This is how the conifer trees get through the winter by relying on the water supplies from the previous summer. The advantage is obvious: in spring, valuable energy does not have to be invested in forming new leaves. As soon as the water in the ground begins to melt, the tree can begin to produce nutritious sugar solution in its needles through photosynthesis. In this way, time is saved, and every minute of the short polar or mountain summer is put to good use. Those not dependent only on a vegetable diet have an advantage in the forest. In winter, more animals perish than in any other season. Such a large carcass quickly attracts competition.
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The bear is put off by some superior forces, while the wolves make it very clear who's in charge around here.
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In the mountain forests of Spain, winter is often just as harsh as in the far north. Griffon vultures, crows, and ravens get stuck into a dead wild boar. Though thousands of kilometers apart, various forest dwellers undertake the same task. The forest offers niches for specialists. Even in the coldest season, life has almost come to a halt; the forest is in hibernation.
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But when the sun starts to shine stronger again, the forest begins to weaken, drop by drop, and with the water comes life once again. Now roots can become saturated once more, so that leaves and needles can soon produce their essential sugar solution.
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Coniferous trees and mosses immediately start photosynthesis, and beneath the snow, winter aconites and snowdrops lie waiting for their big chance.
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Within a few days, the forest is transformed into a paradise.
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Finally, the deciduous trees also begin to sprout, and so the circle is once again complete. All the pieces are in place, and the forest organism is renewed once more.
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Everything has its place here.
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Storks return to Europe in spring and settle into the top floor of the forest. In faraway Kamchatka, on the east coast of Russia, this position is taken by the Steller's sea eagle. It needs a high nesting platform for takeoff and landing; its wingspan is almost three meters. Smaller species can penetrate further into the forest. A hummingbird's nest in the Amazon.
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Birds all over the world are accommodated in arboreal lofts.
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One floor further down, mammals or marsupials have moved in. Koalas in Australia, in Africa, chimpanzees, drills.
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And bonobos.
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Every evening, great apes like these gorillas build themselves a night nest from the branches, just as our own ancient ancestors must have done.
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And finally, in the trunk of the tree, even more animals find a spot. The only premise is that woodpeckers have to build the cavity themselves. They do indeed hammer a hole into the trunk, but the damage is limited. To build its breeding layer, the woodpecker mostly seeks out trees with rotten areas in their cores. First, the bird works its way through the bark; underneath lies the bast, where cells transport sugar solution. The woodpecker recognizes the rotten part of the trunk by the sound of its tapping. At that point, the wood is softer. To get there, the bird often takes year-long breaks, allowing fungus to further soften the construction site. As he hammers on, he reaches the sapwood; here, water is transported from the roots to the leaves by living wood cells. Deeper into the tree, the bird reaches the heartwood; this only serves as support now, as these wood cells have already died. A few channels are indeed broken by the woodpecker's hole, but the majority of the layer is built within the dead heartwood. Round about the nesting hollow, water and sugar solution are still flowing, enough to keep supplying the tree with nutrition. The bird does not harm the tree; on the contrary, it helps to keep insects at bay that live off the wood, well, and others. Once the woodpecker has completed its first construction and has moved away again, other animals are glad to make use of the living space. Over the following years, flying squirrels, for example. They live in the forests of Finland. After a few years, even giants can take advantage of the hollowed-out trees: black bears in North America. A mother has used the tree trunk as a birthing chamber for her cub.
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Former woodpecker cavities make desirable nurseries for common goldeneyes, for instance.
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The nest protects them from ground predators, but also poses a problem: how do the chicks get back down? Their instincts tell them to follow their mother, no matter where she goes. Their bones are so flexible that they very seldom break. Much more dangerous than the fall is the stroll across the forest floor; here, they're at the mercy of predators. Only once they reach the water are they safe from attack. Foxes, meanwhile, prefer life in the basement of the tree. Vixens like to build their dens between the roots. At first glance, the forest appears to profit animals most of all, offering them food and shelter. Yet, this is a two-way transaction. Without the woodpecker, for example, insects under the bark could multiply unhindered, and the forest itself is even more dependent on animals to help it reproduce and expand, such as the squirrel.
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All kinds of stuff fall from the trees in autumn: seeds of various types, and the animals help by spreading them far and wide.
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From chipmunks and mice to red squirrels and ants. Bodies of fat and sugar hang from many of the seeds, acting as a reward. Of course, the animals also consume some of the nuts, but many are plowed in or buried. Beech trees have developed a special way of smuggling as many seeds as possible past the greedy animals. In some years, the trees produce so many beech nuts that the animals are full up long before they've eaten everything on offer. So many of the seeds can germinate in the animals' food stores. Fruit-bearing trees are especially geared towards gaining attention with their juicy and often brightly colored harvest. They easily attract their horticultural helpers. It's a strategy evolved over millions of years. When the cassowary swallows a whole piece of fruit in the Australian bush, the kernel is carried to another location where it is excreted and can then begin to grow again. This is more or less also how it works with fruit eaten by uakaris in the Amazon, or indeed by all other animals the world over.
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One species, however, plays an especially important role in the development of the forests: the flying fox.
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They're nocturnal and head off in the search for food when the sun goes down. These strict vegetarians eat mostly fruit or nectar.
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Flying foxes are said to be responsible for the plantation of their own habitats. Researchers from the Australian Department of the Environment estimate that a single flying fox can distribute around 60,000 seeds per night. Even if only 0.1% of the seeds actually germinate, a single animal would still plant around 22,000 trees every year. One small job for a bat, one giant leap for the forest. The most important element for a forest's survival is water. Without water, there would be no trees, of course. Every life form needs it, but the vegetation in the forest uses water very differently from humans or animals. The forest actually produces its fuel from water. Every tree channels water from the roots to the leaves, when it's transformed into glucose: pure energy food.
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Almost as if humans could create gold from lead, except the sugar trick really does work. Leaf cells contain chlorophyll. This captures sunlight, used to charge up the cell's electrons. The packaged energy is sufficient to then separate the water into hydrogen and oxygen. The hydrogen is combined with carbon dioxide in the air to form glucose, while the oxygen is a byproduct, escaping into the surrounding environment. Luckily for us humans, the sugar solution is distributed throughout the entire tree by its veins. Most of it is channeled to the roots, where any unused solution is stored for times of shortage, so that there's always enough water. The roots saturate themselves whenever they can during rainfall. Some trees manage to take in up to a thousand liters. Yet, the tree has no muscles with which to suck the water up. This is where the so-called capillary effect comes in, by which water flows upwards in narrow tubes. This only works for the first meter, however. Then the tree has to change strategy by vaporizing water through the leaves. A suction effect is created in the veins that draws water upwards. In order to gain enough water for photosynthesis, the tree has to move large quantities. 500 liters flow through a large beech tree every day, and when the water escapes from the leaves, it rises up and falls over the forest again in the form of rain: a never-ending cycle.
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Water vaporization not only causes the typically damp forest climate but also leads to evaporation chill.
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This is how the forest can cool itself and its surroundings by up to two degrees on hot summer days, an effect that benefits entire regions and their populations.
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Throughout the year, the forest produces vast quantities of organic waste.
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Plant remains are eaten by animals or decayed by fungus and bacteria. The recycling chain is long. Ultimately, the tree will rejoin the earth from which it grew, and from which new trees will grow in turn. The land our forests grow on was not always so fertile; it first had to be made that way. As the glaciers of the last ice age retreated, they left behind a jumble of rock, which they had ground down and carried along with them on their journey south. Around 12,000 years ago, the forests began to reclaim this habitat for themselves. At the beginning, only a few plants were able to grow on the so-called glacial till, but the more plants that died, the higher the layer of organic waste, or humus, grew. Just as the composition of the ground changed, so did the forest itself. First, mostly oak trees grew well, then later, beeches. Humans had quickly begun to make use of the humus layer; this meant clearing the forest, however, and that had consequences. A forest clutches the kingdom of the earth tightly in its roots. Rain cannot wash it away; the trees absorb and conserve rain water, thus the forest acts like a sponge.
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When woodland is absent, the results are quickly apparent. In the Scottish Highlands, humans have deforested the wooded hills for centuries.
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There are no more trees there to absorb the water, so it flows unimpeded into the glens, flooding the barren landscape. All plants need water, but some expert species have learned to make do with very little. The Sonoran Desert is a habitat of extreme aridness. Normal trees couldn't survive, but a forest does indeed exist here: a forest of cacti. It takes 65 years for a saguaro cactus to develop its first limb. The lack of water prevents a faster growth rate, and even the cacti cannot get by without any water at all. Two rainy seasons per year bring extreme storms; more rain falls within the shortest time here than a whole year elsewhere. The cacti have adapted to these conditions; they can store as much as they can in their trunks.
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As soon as the water is gone, they have to get through long periods of drought. But the desert cacti are not alone in developing such survival strategies; the indigenous woodland also has some tricks to hand. When it gets too dry in the forest, the forest itself can produce rain.
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The trees open up pores in their leaves, releasing small molecules which rise as aerosols. These particles are necessary for the water present in the air to condense. More and more water molecules adhere to one another; clouds are formed, and when the water droplets become so heavy that they're unable to hover within the cloud anymore, they fall to the ground as rain. This is how the trees work actively together to produce rainfall for the forest itself. But is there such a thing as too much water? In the 19th century, riverbank flooding was a familiar challenge for trees. Humans straightened and diked the rivers; however, only a few alluvial forests remain. Some trees cope badly with such flooding.
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Beech trees can only handle a few days of it before perishing; their delicate roots are starved of oxygen, and they drown.
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Oaks, however, can withstand high water levels over several months.
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In places where water remains permanently, most indigenous trees die off, but some of them can't seem to get enough of it. The spray forest, southeast of Berlin, where older trees grow. In contrast to other trees, alders don't close over the pores on their leaves, so they're constantly vaporizing water and drawing new supplies up from the roots. They consume so much water, in fact, that entire fens can be dried out where they grow. This means land gain for the people living around the spray forest. The Sorbian population here have created their very own water world, regulated by the trees. Older alders feature ideal nesting conditions for cranes. The water offers protection against enemies. Cranes mostly lay two eggs; the first chick has hatched, the second will arrive in the following days. The crane was a symbol of vigilance as early as medieval times. A raccoon dog; he could be dangerous for the chicks. Around 50 years ago, these East Asian wild dogs arrived in Europe, but the raccoon dog can't get anywhere with the watchful adult bird around. In the Everglades of Florida, water is also present the whole year round, an advantage for the birds. They enter into an unusual symbiosis. Alligators hunt in the water, mostly for fish; their egg clutch requires absolute dryness, however. They make their nests on forested islands and stand guard over them. When the little ones hatch, their mother carries them to the water. From now on, she'll look after them for several months. The presence of the alligators also attracts breeding birds who nest in the trees above. Of course, the reptiles also eat birds, but the advantage for the colony prevails. With alligators in the water, the chicks are well protected from predators like raccoons, rats, and lizards. Freshwater environments are already challenging for the woods; saltwater, on the other hand, is even more so. Nevertheless, there is a forest which can manage: the mangrove forest. With the coming and going of the tides, mangrove forests on coasts worldwide are completely submerged twice a day, but the trees don't drown. From their roots, snorkel-like tubes grow that poke up out of the mud. The tubes draw in the necessary for the trees to grow. Perhaps this was the environment of the first creatures to walk on land: walking fish, rather like the mudskipper. Early humans certainly developed in the forests. In deepest Africa, the Congo region around the Great African Rift Valley can be seen as the birthplace of humanity. Even today, our closest relatives still live here: chimpanzees and bonobos. Chimps are only found north of the river Congo.
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Their common ancestors were separated from one another when the valley rift opened and filled with water around three million years ago. The Congo River system was born. Some researchers hypothesize that the bonobos could only evolve because they didn't have to compete with aggressive species such as chimpanzees. The same might even be said for humans. Humans and bonobos have an inherent trait that distinguishes them from the chimps: they can cooperate with strangers.
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So, humankind originated in the forest, a deep-rooted legacy still felt until now.
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The forest has quite evidently shaped us.
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Our sense of sight today can be traced back to our lives among the trees. Mammals can only perceive the woods in shades of green and blue; their eyes lack the sensors necessary to see red. Be it deer or wolf, they have to rely mostly on their senses of smell and hearing to find food or avoid enemies. However, primates in Africa developed sensors to perceive the color red around 30 to 40 million years ago, and suddenly the world looked very different. Yellow and red fruits and leaves were easier to find, and the apes could see whether they were ripe or not. Also, some predators became easier to spot. Scientists surmise that the primates prevailed due to the advantage of the ability to see red, and that this ability was inherited by us humans.
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Early humans were at home in the forest; it offered them shelter and security. They felt comfortable there.
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Even nowadays, the sight of the color green has a calming effect on us, even lowering our pulse rate.
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Two further factors may contribute to our well-being in the forest.
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Through evaporation, the forest atomizes water. This creates negative ions in the air. The effect is disputed, but it could indeed have an influence on our sense of well-being.
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In coniferous forests, a pleasant aroma is radiated, mostly by essential oils. Alpha-pinene, the highly concentrated main element of turpentine oil, is wafted through the air here in delicate amounts. Humans didn't rediscover their love for the forest until relatively recently. Writers first began to idealize the woods during the 19th-century Romantic period. Reforestation has happened again in many places around the world. The notion was spread that the whole of Europe was once upon a time overgrown with thick woodland before mankind came along and chopped it all down. But such an account belongs in the realm of fairy tales. Wild woodland never looked like man-made forest: monotonous plantations of trees in rank and file. Large deforested areas are normally planted again right away. The trees in such a plantation zone are the same age and thus more or less the same size, so they all get an equal amount of sunlight. The ground beneath them is much more shaded, however. Down here, hardly anything grows: no trees, no bushes, just a few shrubs. Only a restricted range of species can get by in these surroundings; that goes for animals as well as plants. When large herbivores come into a forest, they alter it. Clearings are formed where sunlight can also reach beneath the trees. Suddenly, new life is possible at different levels: on the ground, in the shrubs, in bushes, and in trees of various heights. And the diverse habitats attract assorted animals and plants; some like the dense shrubbery, while others prefer the sand. In this way, the open woodland offers living space to more species than the man-made forest. Large herbivores once existed everywhere to maintain open woodland, like bison, for instance. Here in the Caucasus region, the bisons still run wild. Such a herd covers up to 40 kilometers a day. On their way, they eat leaves and shoots, but before the animals eat an entire area empty, they move on again. Thus, they create free space for other species and for trees to grow back. Now, some nature conservation areas are taking advantage of this valuable trait of the big plant-eaters. The aim is to keep the forest as bio-diverse as possible.
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Wild horses are also well-equipped for this purpose. They appeared in the forests of Europe at one time but then became extinct there. Today, several species similar to true wild horses have been returned to the wild in protection areas. Here, they can generally be left alone to multiply. Red deer are the only big mammals left in the Central European forests. They too contribute to keeping the woodland open. Their smaller relative, the roe deer, also helps out. They're not loved by all forest managers, however. While the roe deer prefer high-energy food like fresh buds, the red deer eat lots of grass. Mostly in winter, however, red deer also strip bark from a large number of trees. This can allow fungus to take hold, reducing the value of the wood.
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In Scotland, where the mountain forests were completely stripped and never replanted, a large red deer population now prevents new woodland from growing.
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Here, the large number of deer is desired, as they bring paying tourists to hunt at the grand estates.
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The so-called game browsing is to the detriment of commercial forest, where trees are supposed to generate maximum profit. In the open wilderness, however, game browsing is part of life; it offers woodland the chance to renew itself. Trees all over the world have also developed strategies to prevent animals from grazing too much. In Africa, umbrella thorn acacia trees have armed themselves against the few giants large enough to reach their leaves. As soon as they register that a giraffe or an elephant is nibbling at them, they produce a poison that is transferred to the leaves directly. This makes them inedible for a period of time. On top of that, the affected tree alerts other acacia trees in the surrounding area. Pheromones released into the air act as messengers, so before the elephants or giraffes have reached the next tree, it's already been warned and has started to produce its own poison. The earlier the poison is produced, the fewer leaves the elephant can manage. Arboreal damage limitation in action.
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Trees in the European woodlands speak this aromatic language as well. They also send their signals when caterpillars or beetles start chewing on their leaves or bark. Additionally, the tree uses resin to protect against the bark beetles. If it's only one single beetle, a healthy tree has good chances to ward off the attack. The tree must produce significant amounts of resin, however. The more energy it has to invest in the process, and the earlier it starts, the better. The trees have developed their very own early warning system. When a tree is attacked, it sends out pheromones, tiny carbon compounds that sail through the air to the next tree, like the words of a secret language. In this way, it's likely that the trees can also say what kind of danger is afoot. Scientists have discovered 300 different scent words in German forests alone. By now, around 2,000 such words have been detected worldwide. Exactly how this tree language works is not entirely known, but it's clear that by using this secret communication, trees can take specific measures against various threats. In monocultures, where humans have planted the same tree species over a large area, the system doesn't work. Bark beetles can multiply far too quickly; no man-made forest can withstand such numbers. In wilder woodland, on the other hand, the beetles can only cause individual trees to die. This dead wood is important for the forest; it provides fertile soil for new trees.
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Dead wood brings new life and biodiversity.
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A habitat for insects and a source of nutrition for all of those who can feed on it.
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In Olympic National Park on the west coast of the United States, it's clear where a tree once stood, even decades after its death. Dead wood is good for forests. But what about fire? The flames spread over wide expanses; they don't seem to spare anything. Yet, the woodland animals have developed strategies to escape the fire. Squirrels flee by springing through the treetops. Forest fires are common in California. In 2013, the region around Yosemite National Park was especially badly affected. The fire lasted for 10 weeks and devastated a thousand square kilometers. Even this wasteland is still alive, however. The ashes are rich in nutrients, and lots of seeds only germinate when the heat of a fire wakes them up. Life quickly establishes itself. The white-headed woodpecker uses the tree stump for its nest. The female bird has even found some insects that survive the blaze. For almost a month, the two adult birds have to feed the offspring until they're ready to move out. Luckily, the forest has enough food on offer again, even shortly after the fire. The youngsters are very pushy. The cactus forest of Arizona; it's also developed defense strategies. The water it conserves is highly valuable.
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Those who mess with the cacti bear the marks for a long time, like these peccaries. Cholla sprigs hang from their coats like limpets, and it's painful. The peccaries can only get rid of the birds when they drop off by themselves. Then the sprigs start to grow again where they lie. In this way, the sprigs do double duty.
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Apart from the cactus fruit, there's very little moisture around here. The animals have to put up with the prickles. Squirrels have developed their very own harvesting technique to deal with the barbed plants.
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Success is obviously worth the pain, and one can always take a nice dusty bath afterwards to get rid of any remaining thorns.
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On the other side of the world, some others have also managed to outsmart the plants to secure their place in the woods: koalas in Australia. Eucalyptus leaves are poisonous; this is how the tree protects itself against enemies. No large animals can eat them apart from koalas. They can do this thanks to special digestive bacteria that they use to exploit the leaves. A baby koala cannot manage this right from birth; it first has to acquire the bacteria from its parents. The trick only works with individual leaves from specific types of eucalyptus, ones that don't contain too much poison. With this ability, the koalas have secured themselves a food source unchallenged by large competitors. Plants and animals in the woods have a close relationship with many interdependencies. If the plants develop a strategy, the animals will respond, and vice versa. This is how the forest system largely maintains equilibrium.
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The forest by night is regarded as secretive and mystical. For a long time, no one really knew what trees do at night.
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It was only known that plants also have a day and night rhythm. After all, if flowers are placed in a dark cellar, they still open and close as if they were outside. Charles Darwin discovered that plants let their stems and leaves droop at night and referred to it as sleep. Only recently have scientists detected this behavior in trees as well. 5-meter birch trees let their branches hang down by up to 10 centimeters. The deepest point is reached just before sunrise. This could be caused by the stoppage of water processing overnight. Photosynthesis requires light, of course, and so no water is needed at night to create sugar solution for energy. The leaf pores are left open, however; the tree still has to breathe, so it still needs oxygen. But at night, the oxygen is not self-produced, and so the tree has to extract it from the environment. In return, the tree exhales carbon dioxide. On balance, though, a tree generates so much oxygen that this reverse process is of hardly any consequence. And the trees appear to heavily depend on their sleep. According to research in the United States, trees apparently died after being exposed to light from street lamps. Even when the trees are asleep, the forest itself is always active. A pygmy owl has caught some prey. Around a third of all vertebrates are nocturnal; with invertebrates, it's almost two-thirds. They also help to ensure that the forest system runs smoothly.
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The equilibrium of the forest depends on many factors: light and air and water, and also on the number of herbivores. Too many of them can cause damage. Predators often take on the responsibility of managing their numbers, but even in forests without predators, a balance is maintained. Terrestrial predators like rats and cats were first brought into New Zealand by human settlers. Before that, the forest animals had no enemies. Many birds live close to the ground, like the kakapo. It's the only parrot in the world unable to fly and nests on the ground. The chicks and eggs are easy prey, not least for weasels and ferrets. Farmers introduced them in New Zealand because a plague of rabbits had been brought into the country. In conservation areas, the number of kakapos is steadily increasing; around 150 of them are thriving today. Even the national symbol of New Zealand, the kiwi, is under threat.
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At night, the forest dweller dares to venture out. The bird is an omnivore. It has a special ability, however, in detecting the movement of worms and larvae underground and picking them out with its long beak. Birds were once the biggest plant eaters on the islands here; apart from a few types of bat, there were no mammals or marsupials in the country. So that the woods could maintain their balance, the birds only had to keep the herbivorous insects at bay. Even in places where land predators have been present all along, they don't always correspond to their reputations. In the mountain forests of northern Spain, brown bears wander the slopes.
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They don't keep the number of herbivores in check because they mostly eat plants themselves. In Sweden, scientists have determined exact numbers. Bears there cover around half of their yearly food requirement by consuming berries; around a third is made up of plants and insects, and only a fifth of large herbivores. Only seldom do bears prey on adult moose; normally, it's the calves they kill. And not every meat-based meal in the statistics has been killed by the bears themselves; they'll also make do with moose that have already died. They even jostle with wolves for the privilege.
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In Europe, the wolf should be seen as a welcome homecomer. They're the only animals capable of truly restricting the number of deer. Wherever wolves are found, browsing damage in the forests is controlled.
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So, they really do work towards an equal balance.
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Sometimes, however, a wolf will leave the woods to hunt. They only need the trees during daytime to hide from humans. In contrast to the wolves, there are predators who have perfectly adapted to the woodland environment and who will only hunt in the forest. In Europe, that means the lynx. They lie in ambush until their prey is close enough. In South America, the jaguar follows the same tactic. He can only prowl close enough to the caimans by staying under cover, then he has to wait. Jaguar and lynx could only develop as ambush predators thanks to the cover of the forests. The forest is the ideal place for all those who need to keep hidden. The red deer has noticed the lynx and makes off, while the caimans are now within the jaguar's reach. He's still invisible to them, however, and the roe deer is also too late in its detection of the lynx. A life and death struggle begins for the jaguar, while the lynx has already emerged victorious. The jaguar does eventually also kill his prey, albeit in an alien environment. Both lynx and jaguar depend on the woods for hiding places, in keeping with their hunting strategies. Other animals hide away in the trees in order not to be eaten. Camouflage is the key to their survival.
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But the hunters also know the tricks.
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Australia's death adder creates a fake worm with its tail, an ingenious trap for prey, and the trick works.
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In the modern world, the forest is often the last sanctuary away from human beings. At night, though, many animals dare to emerge from their hideouts. In daytime, it's not only the wolves that withdraw back into the woodland.
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Red deer were not originally forest dwellers; as grass eaters, they lived in the open landscape. In Scotland, these creatures are moving back to their earlier lifestyles, even though they're still being hunted. They don't have any other choice now that the forests are gone. While humankind has hunted many species to extinction, there's always a surprise or two still in store.
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Deep in the forest, where humans couldn't venture, something survived.
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This is the first footage of Cross River gorillas. Until the end of the 1980s, scientists believed this subspecies of western gorilla to be extinct.
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Even today, they're hard to find. Around 250 of them still live in the borderlands between Nigeria and Cameroon.
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Florida forests also harbor the last of a kind: the Florida panther, a subspecies of puma. Camera traps deliver the few images from the wilderness. In 1970, only 20 animals were still living here; today, however, it's around 150. The forest is often the last refuge for animals. In the national parks of Africa, lions normally live in the savannah; they have nothing to fear and show themselves openly. Even if they start out cute and cuddly, they grow into the biggest terrestrial predators on the continent.
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In Ethiopia, on the other hand, the king of the animals occasionally lives as a recluse, high up in the mountain rainforest. The jungle lions were first photographed in 2012 and finally filmed in 2015. As far as experts know, these are the only lions living in a rainforest. They're probably just passing through, but more research is necessary to find out further details. In the forests of Australia, one can also find some rather unexpected animals. Everyone knows the red kangaroo, yet these animals only evolved after Australia's rainforests had declined and when animals thus had to cover wide distances to find food.
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Where the rainforest still thrives in Australia today, a much older type of kangaroo can be found.
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High up in the branches, the tree kangaroo nibbles on leaves and raises its offspring, constantly in danger of the young animals falling down. But there's always food available. This kangaroo never has to learn how to take giant leaps; much more important are the strong claws that allow the animals to hold on to the tree trunks and that also help to prevent the infants from falling off.
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Once a species has become adapted to life in the forest, they die off if the woodland disappears.
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In Scotland, the capercaillie is struggling for survival. The pitiful remains of the Caledonian Forest are not sufficient to support their population. Scottish wild cats are also on the way; hardly a hundred animals remain in the Highlands today. They're similar in appearance to European wild cats, but they're so uncommon that no film footage of them exists. The biggest problem of the Highland tigers, as they're lovingly referred to, is stray domestic cats with whom they mate. In this way, their species could soon disappear, absorbed into the large gene pool of the house cats. Woof! Significant biodiversity can only be found in parts of Europe where unspoiled woodland is still growing.
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The rare stag beetle lives on oak trees. Its larvae need rotten dead wood, while the beetle itself feeds almost exclusively on oak tree sap. Even hornets can't put him off. Only when he meets a competitor do things get serious. The two beetles fight for the right to mate with the females on the tree. He who falls off has lost, and the victor claims his bride.
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Virtually everywhere on the planet, the life of the forest is determined by the seasons. They dictate fixed appointments for the forest, since day length is more decisive than pure temperature, and because day length changes at the same time each year.
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An equality of day and night marks the start of autumn. At this point, day and night are each 12 hours long, all over the world.
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Afterwards, the days become shorter than the nights.
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As soon as the trees get too little light, their leaves begin to change color. Thus, the cosmos decides what happens in the forest.
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The color display of the autumn leaves is beautiful, but beauty is not the main purpose. There is a practical reason for the show.
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Water is vaporized via the leaves of deciduous trees; only in this way can the suction system be maintained that draws water up to the leaves from the roots.
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In winter, this doesn't work, since the water in the ground is frozen and the roots cannot maintain supplies. When the water is evaporating through the leaves, the tree would dry out. That's why the tree seals off the connection between branches and leaves. Without water, the leaves will quickly dry out and drop off. But wait, before the tree cuts off the path to the leaves, it extracts their most valuable element: chlorophyll. That must not be wasted. While the green chlorophyll is taken out, other substances become visible that were previously hidden beneath it. One of them is the orange-yellow carotenoid. Everyone knows it; it's the stuff that gives carrots their distinctive color. On some trees, the leaves even become red or violet. In these cases, it's anthocyanin left behind that gives cherries, grapes, and red cabbage their color. Finally, the wind dries the leaves out. The tree remains well protected, falling into a state of winter rest until the temperatures rise again and the days become longer.
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Forests have left their mark on the face of the planet for millions of years. It's astonishing how they have managed to spread to almost all corners of the Earth, even where one least expects it. The trees have sent out scouts and gained a foothold.
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On the rock pinnacles of Saxon Switzerland, the forest makes use of every crack that's gathered a bit of earth over the years. A tree can then grow as a vanguard. Breathtaking.
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In Yosemite National Park, woodland has grown over a rocky landscape, a formidable achievement. Beneath the thin layer of earth, there's nothing but stone piled up by the erosion of the mountains. On the coasts, where forest meets salt water, it's exposed to an aggressive climate. With the low salt content of the Baltic Sea, however, some indigenous trees get along for a while. They've managed to fight their way to the flood mark, even defying the sand until it finally swallows them up. But a forest never gives up. In the subtropics, it has even grown into the mud flats, and wherever it spreads, its inhabitants follow, even north of the polar circle.
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For us humans, the forests are essential for our survival. Wherever they grow, they produce oxygen. Yet, humans continue to destroy woodland. We lose 90 square kilometers of it worldwide every day.
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Faced with this situation, it doesn't even matter that dwarf birch trees have managed to establish themselves beyond the tree line. The forest is incredibly resistant; if it's driven back, it always finds ways to spread out once again. Many elements in the woods combine to create a unity. Be it animal or plant, everything unwittingly takes on a role that contributes to the functioning of the whole system.
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If the forest's environment changes, its occupants will likewise alter themselves, but the woodland itself remains in perfect balance. It's adapted over millions of years to climate and weather.
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The forest has managed to win through. Does that mean it's a living organism? The cooperation of its many parts does not follow a prescribed goal; it rather seems to be guided by coincidence. All the same, it has turned the forest into perhaps the most successful ecosystem on Earth, a system we have a duty to protect.
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