Did you think that a tree was limited to branches and leaves? Enter the fascinating world of spruces, lime trees and oaks, a forest of mutual aid and competition where trees flourish thanks to a thousand ingenuities.
In The Lord of the Rings, JRR Tolkien imagines tree-like characters, the Ents, who watch over the forests. If they move and communicate, it is only very slowly. Pure fantasy, the Ents? Not so sure, reading the work of the German forester Peter Wohlleben, who invites us to reconsider our “vegetative” conception of trees.
The tree, this stranger
First, some fascinating data. A stump whose trunk was cut down four or five centuries ago remains alive, thanks to exchanges with neighboring trees. As revealed by carbon-14 dating, a spruce in Dalarna, Sweden, has reached the astonishing age of 9,550 years. The aspen in Fishlake National Forest in the United States has a root system that covers 43 hectares and contains 40,000 trunks.
A tree is made up of leaves, branches and roots, but it is also the fungi with which these roots live in symbiosis to colonize the soil, the contacts with the roots of trees of the same species, the exchanges of nutrients and information that result from it. For its formation, the trunk mobilizes a considerable amount of energy, but it is the means of having access, before other plants, to the light necessary for photosynthesis, and of escaping herbivores.
This trunk is an unusual feat. Even today, we do not know how the raw sap – water and minerals drawn from the soil by the roots – can reach the top at 15, 25, or even 40 meters high. Made of wood, an inert tissue of dead cells, it is prey to fungi and bacteria. The same is true of living tissues, whose richness in nutrients arouses covetousness.
To protect itself, the tree secretes an extremely resistant tissue: the bark. If the bark is damaged, a chase begins. The tree must try to rebuild it before the inert tissues are seriously damaged and colonized. The vigor of the tree is a decisive factor. A weakened tree (by soil compaction, water stress or any other climatic event) risks losing the game.
Another physical problem: exposure to wind, the thrust of which, during storms, can reach 200 tons. Trees that have grown without a hitch have a coefficient of air penetration better than that of the most efficient cars, provided they no longer have leaves! Hence the interest in losing them in the fall, but also the danger of summer tornadoes.
Social beings
Trees are social beings capable of helping each other, and the forest is the right level of observation. They form communities and have co-evolved in and for this environment. Thus, trees produce their own protective environment. In the event of a storm, the diversity of trunks will increase resistance. Trees do not sway in the same way, they collide and thus mutually attenuate the oscillations and the risks of uprooting. A monoculture of clones is much more sensitive to tornadoes than a dense natural forest.
In the event of an insect attack, a subject will secrete bitter toxins that dissuade the enemy from continuing. They will cause neighboring trees of the same species to produce the same toxins, protecting them in advance from the attack. We can speak of an “alert system.” The transfer of electrical messages in the root membranes is also suspected. Finally, it is common for a parent tree to feed, through its roots, the offspring trees that are nearby and that wait, in the shade, for a large tree to fall to take flight. A sort of nursery, to ensure renewal in good time.
Let us not imagine, however, a community of altruists. The different species of trees are in permanent competition for access to light. In the regions of northern Europe, the beech imposes its dominance. Able to grow in the shade of other trees, it surpasses them in size when adult and mercilessly intercepts 97% of the light. How have the other species managed to coexist? The beech has its weaknesses and its requirements, which leave windows of opportunity.
The yew tolerates shade and can live for a thousand years; it waits for a large neighbour to die, to enjoy a century of light at the end of which it will wait again. The alder or the willow are happy to have their feet frequently under water and are abundant in flood zones. Pines tolerate extreme cold. The birch’s strategy is simple: its seeds are exceptionally light and spread over dozens of kilometres, taking advantage of the first light space to grow and multiply at an unmatched speed. Therefore, when it is outclassed by slower and more powerful colleagues, it has already fulfilled its reproductive mission. Finally, the oak is a formidable opportunist that is satisfied with very diverse conditions.
Each one finds a place in time and space, giving the forest great stability.
The ecological functions of the forest
With the exception of pioneer trees such as birch or linden, trees like to grow in the forest within their community and are in a stressful situation as soon as they are isolated. We therefore preferred, for urban trees, pioneer species that are better suited to aggressive conditions (heat, pollution, solitude). However, these pioneer species have in common the fact that they produce abundantly very light seeds necessary for colonization, much to the dismay of allergy sufferers!
Forests, as we know, play a major role in both the constitution of the atmosphere and in regulating the climate. But they also have a crucial function in the rainfall regime. The water from clouds formed above the ocean barely penetrates more than 600 km into the continental masses. Forests, through their role in the constitution of soils, store water in the continental parts, then, through evapotranspiration, form continental clouds that penetrate further and allow the formation of a new forest that continues the natural colonization. A forest water front is advancing to conquer the continents.
By destroying coastal forests, man is causing the regression of this water front and, in the long term, the drying out of all the continents. The phenomenon is already perceptible in Australia and the Amazon, and it has probably contributed, in China, to the process of desertification that is accelerating today. To stop desertification, we must therefore start by replanting the coastal areas.
A naturalist plea
The functioning of forests is even less understood than that of the ocean floor, and the knowledge accumulated in recent years has profoundly shaken forestry theories. Among the received ideas that Peter Wohlleben dispels, there is that according to which a plantation of young trees (less than 100 years) would be more productive than a formation of mature trees (more than 100 years). In fact, trees continue to grow, if not to grow, and the mass of organic matter produced per hectare is greater in natural forests than in artificial forests, whose trees are generally cut relatively young (between 50 and 120 years depending on the species) for human consumption.
Peter Wohlleben therefore effectively argues for gentler forestry – the controlled high forest, which he considers to be the forest equivalent of organic farming – and the preservation of forest areas left to their natural evolution. He also argues for legal recognition of the living nature of trees. We can only agree with him on this point, while regretting that he did not conduct a global analysis of the use of wood in the world and the overconsumption of forest products – particularly paper – even if he briefly mentions it at the end of the book.
Sustainable management of Europe’s forests must not be done to the detriment of equatorial forests. Our gluttony for paper and cardboard is the cause and, to use the hierarchy established by the négaWatt association in terms of energy, the order of priorities should be: sobriety, efficiency and sustainable management. No managed high forest will be possible if we continue the society of waste. It is because we will save resources that we will be able to manage them well. While rightly raising our awareness of forest issues, P. Wohlleben’s remarks lack the vigor to denounce the structural problem of our hyperconsumption.
The question of anthropomorphism
One of the book’s strengths is that it touches our sensitivity by flirting with anthropomorphism. The tree feels, suffers, communicates. Does it have a brain, wonders Peter Wohlleben? The process is effective, but isn’t the problem being tackled from the wrong end? Convincing humans that plants (after animals) resemble them is a contradiction in terms. It is not trees and animals that resemble us, it is we who belong to the great cohort of living beings and share common traits.
Living beings maintain relationships with their environment, physical, chemical, biological relationships. None can avoid, for want of disappearing as a species, reacting to changes in this environment, which means having sensors, adapting its physiology, interacting with other organisms. The way in which man communicates with his environment and his loved ones – through the gaze, conscious thought, speech, the formation of feelings – is a modality of this general aptitude of the living.
The problem is therefore not whether trees “feel” or “think” in a more or less similar way to humans, but rather to situate the way humans perceive and process information in the diversity of solutions. A little anthropomorphism can help us emerge from our narcissistic cocoon, but this anthropomorphism remains a sequelae of our anthropocentrism. It is not living beings that are like humans, it is humans who belong to the world of the living.
This remark aside, reading this book – remarkably translated – will allow us to live our next hike in the forest with even more intensity and respect. The author does a salutary work of popularization and highlights the many works that, without him, would have remained unknown to the public. P. Wohlleben (a name that translates into French as “good life”) acts in this matter as an intellectual mycelium connecting the trees of knowledge. We are not very far from the great ash tree Yggdrasil, from which Norse mythology assures that Odin obtained clairvoyance in exchange for an eye.