Trees Are Plumbed Into Each Other by Fungi

Dig up a tree root, wash it carefully, and you will not find bare wood. You will find it sheathed in pale fungal threads, so fine that a teaspoon of forest soil can hold kilometres of them. The arrangement is ancient and almost universal: the fungus takes sugar from the tree and gives back water and minerals it is far better at collecting.

The strange part is that those threads do not stop at one tree. The same fungal individual can wrap the roots of several, and researchers have tested what that means by feeding one tree carbon dioxide made with a traceable form of carbon. Days later the tracer turns up in neighbouring trees, having travelled underground rather than through the air.

How much of that matters is genuinely argued about. Some read it as a forest sharing its resources, with big trees supporting shaded seedlings. Others point out that the fungus is not a charity and takes its cut, and that a network which moves sugar can also move parasites. The measurements are solid; the story we tell about them is still being negotiated.

Either way, the picture of a forest as a crowd of individuals competing for light is wrong at the ankles. Underneath, the whole wood is plumbed together, and something is being moved around down there whether we have agreed on the reason or not.