Tuesday, May 22, 2012

No Tree is an Island

The small seed fell on the fertile soil. After a rest period it swelled and burst out of its case. It lifted its head and began to grow, enjoying the sunshine and the rain water that penetrated the ground and bathed its small roots. After a number of years, it became a significant member of the forest, as large as some of its companions. It had become a tree. And that is what we will call it from now on: Tree.

Tree follows an annual routine, each spring it covers itself with flowers, the agents of a special contract with insect partners. It lures these partners with the perfumed and brightly colored flowers. Tree provides them with nectar and pollen and makes use of them to have its pollen carried to other members of its species. The tiny partners are unaware of the pollination service they provide. Tree uses them for its own purposes, to ensure the next generation and pays them handsomely.

Once the flowers are pollinated, fruits grow, with seeds inside that will complete the process of starting another generation. When the seeds are ready, Tree resorts to other kind of attractants to call a second set of partners. The fruits ripen, become sweet and nutritious and their colors turn bright inviting birds and maybe squirrels or other small creatures as well as larger ones. Tree provides them with sugars and vitamins, to induce them to carry the seeds some distance, so Tree's descendants can spread far and wide.

Tree has relationships with many other members of the forest. Some are not so friendly; they can even be costly.  Tree resorts to other items in its tool kit, including weapons and even hiring some allies of a different sort. Multiple creatures feed on the leaves and other tissues of Tree. Most of the time they don't cause serious damage because Tree uses its defenses to be unpalatable, thus repelling a good number of them or limiting how much they can eat. If things get out of hand Tree resorts to another defense: it calls helpers, parasitic wasps, ready to lay their eggs on the damaging insects, thus bringing down their populations and the damage that they might inflict on Tree otherwise. If that defense isn't enough, Tree can count with the help of several other enemies of its enemies, ladybugs, lacewings and a few others. Tree doesn't know it, but even its enemies may provide it some benefits. Some of them end up feeding the very birds that at other times take care of dispersing Tree's seeds. So, it would be more appropriate to regard them as taxes, that necessary evil, rather than enemies.

Thus, Tree is intertwined to the life of the forest in multiple ways above ground. It is time that we take a look below ground, where the web of life is just as intricate or even more so.

There are certain fungi, called mycorrhizae, that partner with Tree in an intimate way. They are composed of very thin threads similar to rootlets but thinner and far more abundant. They form an endless mesh wrapping around Tree's roots and even penetrating them. They are not a threat but helpers. They dramatically increase the reach of Tree's rootlets and they are far superior at extracting water and essential minerals from the soil.

They render some of these to Tree which, in return, pays its partner with nutrients produced by its leaves. Not satisfied with that, mycorrhizae reach out to other trees and plants, providing similar services. The remarkable thing is that they have the faculty of carrying nutrients from one plant to another when a particular one is under stress and the others are doing well. Thus, the partnership goes well beyond Tree to the entire community.

Mycorrhizal interconnections don't stop there. They also interact with a variety of soil bacteria. These bacteria, too, are very good at producing an assortment of chemicals, some of them useful to the mycorrhizae and also to Tree.

When mycorrhizae want to reproduce, they form the familiar mushrooms often seen on the forest floor. Other mycorrhizae produce truffles instead. Now, it is time for another partner to enter the scene. The mushroom or truffle is nutritious to many forest creatures, beetles, squirrels, flying squirrels. They seek the mushroom or truffle's flesh, swallowing some spores along with it. Later on, they pass the spores at some distance, where new mycorrhizae can grow away from the parent and develop a relationship with other plants.

Tree sheds its leaves every year. These would accumulate to the point of smothering the soil if it wasn't for the work of other helpers. A wide array of insects, fungi, bacteria, nematodes slowly chews away all this matter. It takes them years to return all the nutrients to the soil but they accomplish this task.

I probably left out many other partners of Tree. But this could suffice for now. We can firmly conclude that no tree is an island. No other creature is an island either, all joined together in the Web of Life.

© Beatriz Moisset. 2012

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