Wood Wide Web: How Fungi Shape Our Forests

Excerpted from the The Secrets of the Wood Wide Web

Wood Wide Web graphic of tangled forest Merlin Sheldrake, an expert in mycorrhizal fungi, is part of a research revolution that is changing the way we think about forests. For centuries, fungi were widely held to be harmful to plants, parasites that cause disease and dysfunction. More recently, it has become understood that certain kinds of common fungi exist in subtle symbiosis with plants, bringing about not infection but connection.

These fungi end out gossamer-fine fungal tubes called hyphae, which infiltrate the soil and weave into the tips of plant roots at a cellular level. Roots and fungi combine to form what is called a mycorrhiza: itself a growing-together of the Greek words for fungus (mykós) and root (riza). In this way, individual plants are joined to one another by an underground hyphal network: a dazzlingly complex and collaborative structure that has become known as the Wood Wide Web.

The relationship between these mycorrhizal fungi and the plants they connect is now known to be ancient (around four hundred and fifty million years old) and largely one of mutualism—a subset of symbiosis in which both organisms benefit from their association. In the case of the mycorrhizae, the fungi siphon off food from the trees, taking some of the carbon-rich sugar that they produce during photosynthesis. The plants, in turn, obtain nutrients such as phosphorus and nitrogen that the fungi have acquired from the soil, by means of enzymes that the trees do not possess.

Wood Wide Web graphic of tangled forest The implications of the Wood Wide Web far exceed this basic exchange of goods between plant and fungi, however. The fungal network also allows plants to distribute resources—sugar, nitrogen, and phosphorus—between one another. A dying tree might divest itself of its resources to the benefit of the community, for example, or a young seedling in a heavily shaded understory might be supported with extra resources by its stronger neighbors.

Even more remarkably, the network also allows plants to send one another warnings. A plant under attack from aphids can indicate to a nearby plant that it should raise its defensive response before the aphids reach it. It has been known for some time that plants communicate above ground in comparable ways, by means of airborne hormones. But such warnings are more precise in terms of source and recipient when sent by means of the myco-net.

All of the trees will have mycorrhizal fungi growing into their roots. You could imagine the fungi themselves as forming a massive underground tree, or as a cobweb of fine filaments, acting as a sort of prosthesis to the trees, a further root system, extending outwards into the soil, acquiring nutrients and floating them back to the plants, as the plants fix carbon in their leaves and send sugar to their roots, and out into the fungi. And this is all happening right under our feet.

Wood Wide Web graphic of tangled forest A group of plants called mycoheterotrophs, or “mycohets” for short are plants that lack chlorophyll, and thus are unable to photosynthesize, making them entirely reliant on the fungal network for their provision of carbon. These little green-less plants plug into the network, and somehow derive everything from it without paying anything back, at least in the usual coin. They don’t play by the normal rules of symbiosis, but we can’t prove they’re parasites.

A central debate over the Wood Wide Web concerns the language used to describe the transactions it enables, which suggest two competing visions of the network: the socialist forest, in which trees act as caregivers to one another, with the well-off supporting the needy, and the capitalist forest, in which all entities are acting out of self-interest within a competitive system. Sheldrake was especially exasperated by what he called the “super-neoliberal capitalist” discourse of the biological free market.