Before we take a closer look at some of these creatures, I’d like to take you back to when soil was first created. Without soil there would be no forests, because trees must have somewhere to put down roots. Naked rock doesn’t work, and loosely packed stones, even though they offer roots some support, cannot store sufficient quantities of water or food. Geological processes—such as those active in the ice ages with their sub-zero temperatures—cracked open rocks, and glaciers ground the fragments down into sand and dust until, finally, what was left was a loosely packed substrate. After the ice retreated, water washed this material into depressions and valleys, or storms carried it away and laid it down in layers many tens of feet thick.
Life came along later in the form of bacteria, fungi, and plants, all of which decomposed after death to form humus. Over the course of thousands of years, trees moved into this soil—which only at this stage can be recognized as such—and their presence made it even more precious. Trees stabilized the soil with their roots and protected it against rains and storms. Erosion became a thing of the past, and instead, the layers of humus grew deeper, creating the early stages of bituminous coal. While we are on the subject of erosion: it is one of the forest’s most dangerous natural enemies. Soil is lost whenever there are extreme weather events, usually following particularly heavy downpours. If the forest soil cannot absorb all the water right away, the excess runs over the soil surface, taking small particles of soil with it. You can see this for yourself on rainy days: whenever water is brownish in color, this means it is carrying off valuable soil. The forest can lose as much as 2,900 tons per square mile per year. The same area can replace only 290 tons annually through the weathering of stones underground, leading to a huge annual loss of soil. Sooner or later, only the stones remain. Today, you can find many such depleted areas in forests growing in exhausted soils that were cultivated centuries ago. In contrast, forests left undisturbed lose only 1 to 14 tons of soil per square mile per year. In intact forests, the soil under the trees becomes deeper and richer over time so that growing conditions for trees constantly improve.36
This brings us to the animals in the soil. Admittedly, they are not particularly attractive. Because of their small size, most species cannot be detected with the naked eye, and even if you go out armed with a magnifying glass, you won’t have any luck. It’s certainly true that beetle mites, springtails, and pseudocentipedes are not nearly as engaging as orangutans or humpback whales, but in the forest, these little guys are the first link in the food chain and can, therefore, be considered terrestrial plankton. Unfortunately, researchers are only peripherally interested in the thousands of species discovered so far and given unpronounceable Latin names. Countless more species are waiting in vain to be discovered. Perhaps, however, we can take comfort from this: there are still many secrets in the forest that lies directly outside your back door. Let’s take a look at the little that has been brought to light so far.
Let’s take the aforementioned beetle, or oribatid, mites, of which there are about a thousand known species in European latitudes. They are less than 0.04 inches long and look like spiders with inadvisably short legs. Their bodies are two-tone brown, which blends in well with their natural environment: the soil. Mites? That brings up associations with household dust mites, which feed on the flakes of skin we shed and other waste products and may trigger allergies in some people. At least some of the beetle mites act in a similar way around trees. The leaves and fragments of bark trees shed would pile up several yards deep if it weren’t for a hungry army of microscopic creatures ready to pounce on the detritus. To do this, they live in the cast-off leaf litter, which they devour voraciously. Other species specialize in fungi. These creatures crouch in small underground tunnels and suck the juices that ooze out of the fungi’s fine white threads. Finally, beetle mites feed on the sugar trees share with their fungal partners. Whether it’s rotting wood or dead snails, there is nothing that doesn’t have its corresponding beetle mite. They appear everywhere at the intersection between birth and decay, and so they must be considered essential components of the ecosystem.
Then there are the weevils. They look a bit like tiny elephants that have lost their enormous ears, and they belong to the most species-rich family of insects in the world. In Europe alone there are about 1,400 species. For the weevils it’s not so much about eating as it is about child care. With the help of their long snouts, the little creatures eat small holes in leaves and stems, where they lay their eggs. Protected from predators, the larvae gnaw little passages inside the plants and grow in peace.37
Some species of weevil, mostly those that live on the forest floor, can no longer fly because they have become accustomed to the slow rhythms of the forest and its practically eternal existence. The farthest they can travel is 30 feet a year, and they really don’t need to be able to travel any farther than that. If the environment around a tree changes because the tree dies, all a weevil has to do is make it to the next tree and continue nibbling around there in the rotting leaf litter. If you find weevils, you can be sure the forest has a long uninterrupted history. If the forest was cleared in the Middle Ages and later replanted, you won’t find these insects, because it would simply have been too far for them to walk to the next old forest.
All the animals I have mentioned so far have one thing in common: they are very small and, therefore, their circle of influence is extremely limited. In the large old-growth forests that once covered Central Europe, this didn’t matter at all. Today, however, people have altered most of the forests. There are spruce instead of beeches, Douglas firs instead of oaks, young trees instead of old ones. The new forests were literally no longer to the animals’ taste, and so they starved and local populations died out. However, there are still a few old deciduous forests that act as refuges where the original diversity of species still exists. All over Germany, forestry commissions are trying to grow more deciduous than coniferous forests once again. But if mighty beeches are to herald change and stand once again where spruce now topple in storms, how will the beetle mites and springtails get back to these places? Not by walking there, that’s for sure, because they cover barely 3 feet in a lifetime. So is there any hope at all that one day, at least in national parks such as the Bavarian Forest, we will once again be able to marvel at authentic old-growth forests? It is entirely possible.
Research carried out by students in the forest I manage has shown that microscopic organisms—at least those associated with coniferous forests—can cover astonishing distances. Old spruce plantations show this particularly clearly. Here, the young researchers found species of springtails that specialize in spruce forests. But my predecessors here in Hümmel planted such forests only a hundred years ago. Prior to that, we had predominantly old beech trees, just like everywhere else in Central Europe. So how did these conifer-dependent springtails get to Hümmel? My guess is that it must have been birds that brought these terrestrial creatures as stowaways in their plumage. Birds love to take dust baths in dead leaves to clean their feathers. When they do this, tiny creatures that live in the soil must surely get trapped, and they are then unloaded during a dust bath in the next forest. And what works for animals specialized for spruce probably also works for species that love deciduous trees. If in the future, more mature deciduous forests are allowed, once again, to develop undisturbed, then birds can see to it that the appropriate subletters show up again as well.
In any event, the return of the teeny little creatures can take a very, very long time, as the latest studies out of Kiel and Lüneburg attest.38 More than a hundred years ago, oak forests were planted on the Lüneburg Heath on what had once been arable land. It would take only a few decades for the original framework of fungi and bacteria to settle the soil once again—or so the scientists assumed. But far from it. Even after this relatively long time, there are still gaping holes in the species’ inventory, and this deficit has grave consequences for the forest, as the nutrient cycles of birth and decay are
n’t functioning properly. Moreover, the soil still contains excess nitrogen from the fertilizers once used there. True, the oak forest is growing more quickly than similar stands of trees located on ancient forest soil, but it is markedly less robust when it comes to issues such as drought. We don’t know how long it will take until true forest soil is created once again, but we do know that a hundred years is not enough.
To make it possible for this regeneration to happen at all, you need preserves with ancient forests free from any human interference. These are places where the diversity of soil life can survive, and these refuges can be the nucleuses for recovery in surrounding areas. And, incidentally, no real sacrifices need to be made to make this happen, as the community of Hümmel has demonstrated for years. They have put entire old beech forests under protection and found innovative ways to market them. Part of the forest is used as an arboreal mortuary, where the trees are leased out as living gravestones for urns buried under them. To become part of the ancient forest after death—isn’t that a wonderful idea? Another part of the preserve is leased to firms as their contribution to protecting the environment. This makes up for the fact that the wood itself is not being used, and both people and Nature are happy.
Efforts to offset the costs of protecting and restoring forests in the twenty-first century are happening around the world. Some combine utility with education: tourists in the Maya Biosphere Reserve in Guatemala employ residents who would otherwise be cutting down forests to sell the lumber and grow food in the clearings. Some combine prestige with preservation: in Scotland, you can buy a piece of forest originally owned by the nobility to keep lumber companies out and help usher in the return of the ancient Caledonian Forest. Yet others involve unlikely partners: the U.S. Department of Defense contributes to the National Fish and Wildlife Foundation’s efforts to restore longleaf pine ecosystems in the American southeast on the grounds that forested buffers around military bases contribute to military readiness.39 There are so many ways that forests can be kept both undisturbed and productive!
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— CARBON DIOXIDE VACUUMS —
IN A VERY simple, widely circulated image of natural cycles, trees are poster children for a balanced system. As they photosynthesize, they produce hydrocarbons, which fuel their growth, and over the course of their lives, they store up to 22 tons of carbon dioxide in their trunks, branches, and root systems. When they die, the same exact quantity of greenhouse gases is released as fungi and bacteria break down the wood, process the carbon dioxide, and breathe it out again. The assertion that burning wood is climate neutral is based on this concept. After all, it makes no difference if it’s small organisms reducing pieces of wood to their gaseous components or if the home hearth takes on this task, right? But how a forest works is way more complicated than that. The forest is really a gigantic carbon dioxide vacuum that constantly filters out and stores this component of the air.
It’s true that some of this carbon dioxide does indeed return to the atmosphere after a tree’s death, but most of it remains locked in the ecosystem forever. The crumbling trunk is gradually gnawed and munched into smaller and smaller pieces and worked, by fractions of inches, more deeply into the soil. The rain takes care of whatever is left, as it flushes organic remnants down into the soil. The farther underground, the cooler it is. And as the temperature falls, life slows down, until it comes almost to a standstill. And so it is that carbon dioxide finds its final resting place in the form of humus, which continues to become more concentrated as it ages. In the far distant future, it might even become bituminous or anthracite coal.
Today’s deposits of these fossil fuels come from trees that died about 300 million years ago. They looked a bit different—more like 100-foot-tall ferns or horsetail—but with trunk diameters of about 6 feet, they rivaled today’s species in size. Most trees grew in swamps, and when they died of old age, their trunks splashed down into stagnant water, where they hardly rotted at all. Over the course of thousands of years, they turned into thick layers of peat that were then overlain with rocky debris, and pressure gradually turned the peat to coal. Thus, large conventional power plants today are burning fossil forests. Wouldn’t it be beautiful and meaningful if we allowed our trees to follow in the footsteps of their ancestors by giving them the opportunity to recapture at least some of the carbon dioxide released by power plants and store it in the ground once again?
Today, hardly any coal is being formed because forests are constantly being cleared, thanks to modern forest management practices (aka logging). As a result, warming rays of sunlight reach the ground and help the species living there kick into high gear. This means they consume humus layers even deep down into the soil, releasing the carbon they contain into the atmosphere as gas. The total quantity of climate-changing gases that escapes is roughly equivalent to the amount of timber that has been felled. For every log you burn in your fire at home, a similar amount of carbon dioxide is being released from the forest floor outside. And so carbon stores in the ground below trees in our latitudes are being depleted as fast as they are being formed.40
Despite this, you can observe at least the initial stages of coal formation every time you walk in the forest. Dig down into the soil a little until you come across a lighter layer. Up to this point, the upper, darker soil is highly enriched with carbon. If the forest were left in peace from now on, this layer would be the precursor of coal, gas, or oil. At least in larger protected areas, such as the hearts of national parks, these processes continue today uninterrupted. And I’d just like to add that meager layers of humus are not the result only of modern forestry practices: way back when in Europe, Romans and Celts were also industriously cutting back forests and disrupting natural processes.
What sense does it make for trees to constantly remove their favorite food from the system? And all plants do this, not just trees. Even algae out in the oceans extract carbon dioxide from the atmosphere. The carbon dioxide sinks into the muck when plants die, where it is stored in the form of carbon compounds. Thanks to these remains—and the remains of animals, such as the calcium carbonate excreted by coral, which is one of the largest repositories of carbon dioxide on earth—after hundreds of millions of years, an enormously large amount of carbon has been removed from the atmosphere. When the largest coal deposits were formed, in the Carboniferous period, carbon dioxide concentrations were much higher—nine times today’s levels—before prehistoric forests, among other factors, reduced carbon dioxide to a level that was still triple the concentration we have today.41
Where is the end of the road for our forests? Will they go on storing carbon until someday there isn’t any left in the air? This, by the way, is no longer a question in search of an answer, thanks to our consumer society, for we have already reversed the trend as we happily empty out the earth’s carbon reservoirs. We are burning oil, gas, and coal as heating materials and fuel, and spewing their carbon reserves out into the air. In terms of climate change, could it perhaps be a blessing that we are liberating greenhouse gases from their underground prisons and setting them free once again? Ah, not so fast. True, there has been a measurable fertilizing effect as the levels of carbon dioxide in the atmosphere have risen. The latest forest inventories document that trees are growing more quickly than they used to. The spreadsheets that estimate lumber production need to be adjusted now that one third more biomass is accruing than a few decades ago. But what was that again? If you are a tree, slow growth is the key to growing old. Growth fueled by hefty additions of excess nitrogen from agricultural operations is unhealthy. And so the tried and tested rule holds true: less (carbon dioxide) is more (life-span).
When I was a student of forestry, I learned that young trees are more vigorous and grow more quickly than old ones. The doctrine holds to this day, with the result that forests are constantly being rejuvenated. Rejuvenated? That simply means that all the old trees are felled and replaced with newly planted little trees. Only then, according to the current pr
onouncements of associations of forest owners and representatives of commercial forestry, are forests stable enough to produce adequate amounts of timber to capture carbon dioxide out of the atmosphere and store it. Depending on what tree you are talking about, energy for growth begins to wane from 60 to 120 years of age, and that means it is time to roll out the harvesting machines. Has the ideal of eternal youth, which leads to heated discussions in human society, simply been transferred to the forest? It certainly looks that way, for at 120 years of age, a tree, considered from a human perspective, has barely outgrown its school days.
In fact, past scientific assumptions in this area appear to have gotten ahold of the completely wrong end of the stick, as suggested by a study undertaken by an international team of scientists. The researchers looked at about 700,000 trees on every continent around the world. The surprising result: the older the tree, the more quickly it grows. Trees with trunks 3 feet in diameter generated three times as much biomass as trees that were only half as wide.42 So, in the case of trees, being old doesn’t mean being weak, bowed, and fragile. Quite the opposite, it means being full of energy and highly productive. This means elders are markedly more productive than young whippersnappers, and when it comes to climate change, they are important allies for human beings. Since the publication of this study, the exhortation to rejuvenate forests to revitalize them should at the very least be flagged as misleading. The most that can be said is that as far as marketable lumber is concerned, trees become less valuable after a certain age. In older trees, fungi can lead to rot inside the trunk, but this doesn’t slow future growth one little bit. If we want to use forests as a weapon in the fight against climate change, then we must allow them to grow old, which is exactly what large conservation groups are asking us to do.
The Hidden Life of Trees: What They Feel, How They CommunicateDiscoveries from a Secret World Page 8