The Wood Wide Web: How Trees Share Resources Underground

Walk through any forest and you might see individual trees standing apart from one another, each competing for light and space. What you cannot see — what lies entirely underground — tells a very different story.

Beneath the forest floor, an intricate web of fungal threads connects the roots of trees across enormous distances. These threads, known as mycelium, are the underground filaments of fungi. When they intertwine with the roots of trees, they form a partnership called a mycorrhizal network. The fungi help trees absorb water and nutrients from the soil; in exchange, the trees provide the fungi with sugars produced through photosynthesis.

The scale of this network is astonishing. A single teaspoon of healthy forest soil can contain several kilometres of fungal threads. In some forests, virtually every tree is connected to its neighbours through this underground web. Scientists have taken to calling it the Wood Wide Web.

Canadian forest ecologist Suzanne Simard spent decades studying these networks and made a discovery that changed how scientists think about forests. She found that older, larger trees — which she called mother trees — use the mycorrhizal network to share carbon and nutrients with younger, weaker seedlings growing in their shade.

In some cases, a mother tree was found to be connected to hundreds of other trees at once. When a mother tree is dying, it appears to send a pulse of carbon to the seedlings around it — a kind of final gift that boosts their chances of survival. The forest, it turns out, is not a collection of isolated individuals competing for resources. It is something closer to a community.

The network does more than transfer nutrients. Trees also use it to send chemical warning signals. When a tree is attacked by insects or disease, it can release chemicals through its roots into the shared network. Neighbouring trees that detect these signals sometimes begin producing defensive chemicals of their own, even before they themselves are under attack.

This form of underground communication challenges the long-held idea that plants are passive organisms, simply responding to their immediate environment. Trees appear to be monitoring the health of the forest around them and responding in ways that benefit the whole community.

The discovery of the mycorrhizal network has significant implications for how we manage forests. Traditional forestry often removes older trees first, since they are the most commercially valuable. But if mother trees are the hubs of the underground network, removing them could weaken the entire system — disrupting the flow of nutrients and leaving younger trees more vulnerable.

Understanding forests as interconnected systems rather than collections of individual trees is already changing practices in some parts of the world. The more we learn about what happens beneath the soil, the clearer it becomes that a forest is far more than the sum of its trees.