発展環境・自然科学

The World Beneath the Forest

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When people look at a forest, they usually see the trees. Under the ground, however, there is another world. The roots of most trees are wrapped in thin threads of fungi, far finer than the roots themselves. The fungi take sugar from the tree, which the tree has made from sunlight. In return, the threads reach into spaces in the that roots are too thick to enter, and bring back water and minerals. Neither partner could grow as well alone, and this is thought to be hundreds of millions of years old. In the 1990s, a Canadian named Suzanne Simard tested whether these threads might also one tree to another. She covered young trees of two different with plastic bags and gave each a different of carbon gas. Later she measured the trees and found that carbon given to one appeared in the other. The two kinds of tree, it seemed, were passing back and forth through the fungi in the rather than keeping everything for themselves. The idea captured the imagination, and the underground network was soon nicknamed the "wood wide web." books and films described older trees as mothers feeding their young through the , and warned that cutting down the largest trees might the whole forest. Foresters in several countries began to that these trees should be left standing when an area is cut, so that the network below the ground would . Some governments went as far as writing the idea into their guidelines for managing forests. In years, however, a number of scientists have looked again at the . They that fungi roots and that does move between trees, but they say the amounts measured are often small and that the is hard to . Fungi, they out, are not servants of trees; they may take whatever benefits themselves. The picture of a caring forest, these researchers , has run well ahead of what the experiments show. Simard herself has remarked that her findings are sometimes described in ways she never intended.