–by Peter Wohlleben (Sep 31, 2017)
Gardeners often ask me if the trees are growing too close together. Won’t they deprive each other of light and water? This concern comes from the forest industry. In commercial forests, trees are supposed to grow thick trunks and be harvested-ready as quickly as possible. And to do that they need a lot of space and large symmetrical rounded crowns. In regular five-year cycles, any supposed competition is cut down so that the remaining trees are free to grow. Because these trees will never grow old –they are destined to the sawmill when they are only about 100 years old– the negative effects of this management practice are barely noticeable.
What negative effects? Doesn’t it sound logical that a tree will grow better if bothersome competitors are removed so that there’s plenty of sunlight available for its crown and plenty of water for its roots? And for trees belonging to different species that is indeed the case. They really do struggle with each other for local resources. But it’s different for trees of the same species. Beeches are capable of friendship and go so far as to feed each other. It’s obviously not in a forest’s best interest to lose its weaker members. If that were to happen, it would leave gaps, that would disrupt the forest’s sensitive microclimate with tis dim light and high humidity. If it weren’t for the gap issue, every tree could develop freely and lead its own life. I say “could” because beeches, at least, seem to set a great deal of store by sharing resources.
Students at the Institute for Environmental Research discovered something amazing about photosynthesis in undisturbed beech forest. Apparently, the trees synchronize their performance so that they are all equally successful. And that is not what one would expect. Each beech tree grows in a unique location, in conditions can vary greatly in just a few yards. The soil can be stony or loose. It can retain a great deal of water, or almost no water. It can be full of nutrients or extremely barren. Accordingly, each tree experiences different growing conditions; therefore, each tree grows more quickly or more slowly and produces more or less sugar or wood, and thus you would expect every tree to be photosynthesizing at a different rate.
And that’s what makes research results so outstanding. The rate of photosynthesis is the same for all the trees. The trees, it seems, are equalizing differences between the strong and the weak. Whether they are thick or thin, all members of the same species are using light to produce the same amount of sugar per leaf. This equalization is taking place underground through the roots. There’s obviously a lively exchange going on down there. Whoever has an abundance of sugar hands some over; whoever is running short gets help. Once again, fungi are involved. The enormous network act as gigantic redistribution mechanisms. […]
When the trees grow together nutrients and water can be optimally divided among them all so that each tree grow into the best tree it can be. If you “help” individual trees by getting rid of their supposed competition, the remaining trees are bereft. They send messages out their neighbors in vain, because nothing remains but stumps. Every tree now muddles along on its own, giving rise to great difference in productivity. Some individuals photosynthesize like mad until sugar positively bubbles along their trunk. As a result, they are fit and grow better, but they are particularly long-lived. This is because a tree can only be strong as the forest that surrounds it. And there are now a lot of losers in the forest. Weaker members, who would once have been supported by the stronger ones, suddenly fall behind. Whether the reason for their decline si their location and lack of nutrients, a passing malaise, or genetic makeup, they now fall prey to insects and fungi.
But isn’t that how evolution works? you ask. The survival of the fittest? Trees would just shake their heads -or rather their crowns. Their well being depends on their community, and when the supposedly feeble trees disappear, the other lose as well. When that happens, the forest is no longer a single closed unit. Hot sun and swirling winds can now penetrate to the forest floor and disrupt the moist, cool climate. Even strong trees get sick a lot over the course of their lives. When this happens, they depend on their weaker neighbors for support. If there are no longer there, then all it takes is what would once have been a harmless insect attack to seal the fate even of giants. […] “A chain is only as strong as its weakest link”. Trees could have come up with this old craft person’s saying. And because they know this intuitively, they do not hesitate to help each other out.
–Peter Wohlleben from his book The Hidden Life of Trees. [Picture taken form Daily Good: How Do I Love Trees? Let Me Count the Ways…]