A forest is a highly complex symbiotic community made up from plants, animals, bacteria and fungi that is yet hardly understood by humans. Did you know that trees are, just like humans, very social beings? And did you know, that trees actually talk to each other? Well – they don’t really talk, like the walking trees in J.R.R. Tolkien’s “Lord of the Rings” speaking Entish. But what “language” do they speak then?
The small town where I grew up is known as “The town between the forests”, since it is surrounded on three sides by vast forest lands (to the north we even have the largest contiguous linden forest in Europe). Therefore it’s not surprising that I spent a lot of time in the woods during my childhood – and I still love to go there for a walk or hiking – and ever since, I was fascinated by this habitat and its inhabitants (we Germans, for some reason, have a really serious, deep and emotional connection to our forests…we actually go crazy about it sometimes).
When you enter a forest, one of the first things you might notice, is this mix of different smells and scents – for some reason the air seems to be very different in a forest. As scientists discovered, trees (as also other plants) have various ways of communicating with each other and the smell is one of them. For example: when under attack (by pests eating their leaves for instance), most trees release volatile molecules and chemicals, that can warn other trees or plants nearby and make them prepare and “take measures” like producing toxins to keep off insects for example. However, it is not yet been finally clarified, if trees release these scents with the intend to warn their neighbors or if it’s a normal stress-reaction, that the fellow trees in the surrounding area are coincidentally benefiting from. Anyway, this is just the most perceptible but by far not the most important connection that the trees have!
The role of the fungi networks
A much more crucial and far-reaching role is being played by mushrooms! Hereby it’s essential to understand that, what we see as “a mushroom” is just the fruit (or fruiting body) of the living thing that – more precisely speaking – is a fungus; and fungi, for the most part, live underground. There are three different types of living creatures: plants, animals and fungi. Until the late 1960s the fungi were seen as a special type of plants, until science eventually realized that their characteristics and attributes are too different from both: animals and plants, and that they form their own category, or more poetically speaking: “branch on the tree of life”.
Fungi play an essential role in the community of the forest. Their “roots” – or accurate: mycorrhizae (the actual fungi that lives in the soil) – form a huge subterranean network. One individual fungus can penetrate several hectares of forest soil. In that way, they set up a close symbiotic connection with the micro-fauna of the soil (bacteria and small insects) and the roots of the trees and other plants. That’s why some scientists call it the “internet of the forest” or the “Wood Wide Web”.
There are two different types of these mycorrhizal fungi networks: the first ones are called arbuscular (or endomycorrhizal) networks, that penetrate the roots of the plants, they live on. They are mostly to be found in tropical regions with a hot and wet climate. The second type is called ectomycorrhizal network. It surrounds the plant’s roots without penetrating them; this type occurs mainly in the high latitude regions in the northern and southern hemisphere with a rather cool and dry climate. The different fungi “prefer” different types of trees to enter into a bond with and the other way around.
While trees, when they grow their roots, usually bypass their neighboring tree’s roots, to not “get into conflict” with them, the mycorrhizal networks of the fungi enclose the roots of the trees. In this way they are able to exchange information via chemical signals as well as nutrients and minerals like water, carbon, nitrogen or sugars from tree to tree, from tree to fungus and vice versa. The trees also seem to support weaker individuals with nutrients over this network – and older trees even “feed” their seedlings that otherwise wouldn’t stand a chance to grow in the shadow of the forest ground. Furthermore it was found that dying trees release their resources into this network to provide other trees and plants in their proximity. But this network also has its “hackers”, in a sense that some genera of fungi are selfishly enriching themselves with the nutrients of the trees and some tree species in turn send toxins via this network to eliminate or impair the nearby competition, like for example the walnut tree.
Yet, science has not fully understood the whole complexity of this fascinating system, but apparently fungi and their subterranean networks played a crucial role for the spread of the forests on our planet. Therefore it is all the more important, in the face of climate change and increasing environmental pollution, to understand and maintain the functioning of these ancient and complex symbiotic systems that traverse a large part of the earth’s surface.
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