The Trade Under the Forest

Walk through a forest and you see trunks and leaves. Most of the living exchange, though, happens under your boots.

Nearly all forest trees share their roots with fungi. The fungus grows fine threads through the soil, far thinner than any root and far more numerous. Those threads reach into spaces a root could never enter, and they pull out water and minerals such as phosphorus. In return, the tree hands over sugar it has made from sunlight. Neither partner could do the other's work well, so each pays for a service it cannot perform.

Because the threads of one fungus can touch several trees, a forest can be joined underground. Careful experiments have followed marked carbon from one tree into a neighbour through such a link, and that finding is solid.

What the link means is less settled. It is tempting to call the network a system for sharing, as if the trees were feeding the weak ones. But a fungus is not a charity. It is a partner with its own interests, and some of that movement may serve the fungus more than any tree. The connection is proven. The kindness is not.