The Wood Wide Web

A forest might seem like a quiet place where nothing much happens, but did you know that deep underground, in the soil, trees talk to each other? “Watch out for pests, other trees!” warns one being nibbled by bugs. “Could you spare some sugar?” a weak tree asks its neighbors. “Take some extra food,” a mother tree says to young saplings.

Of course, trees don’t really talk in words, but they do communicate — with the help of mushrooms.

A mushroom is the part of a fungus that sticks up above the ground. Thin, white threads grow from its stem deep into the soil. These threads are called hyphae (say HI-fee). Hyphae connect themselves to tree roots. They also stretch from root system to root system, like an underground network. This network may go for miles. In fact, scientists think that about 80% of all plants on land may be linked to some kind of fungus network.

Hyphae pick up nutrients and water from soil. The fungus threads that connect to tree roots share their nutrients and water with the trees. In return, they sip a bit of the sugar the trees make. Sharing helps both trees and mushrooms live. It’s also how trees communicate.

When a tree is being eaten by bugs, it makes chemicals to shoo them away, sort of like bug repellent. The chemicals travel through the tree, down its roots, and into the hyphae network. Other trees connected to the network taste the chemicals. That tells them a nearby tree is under attack, so they start to make their own bug repellent. It’s a bit like seeing a post on your friend’s online story that a strange dog is loose in the neighborhood, so you know to watch out.

Trees do more than share warnings through the hyphae. They also help each other. In the fall, paper birch trees drop their leaves and can no longer make sugar. So, a fir tree that stays green all winter uses the network to send extra sugar to the birch until spring comes again. Then in spring and summer, the birch trees send sugar to fir trees too small to reach the sunlight.

This system of sharing information and nutrients through the hyphae is sometimes called the “wood wide web,” because it works a bit like the Internet. (The “world wide web” is one nickname for the Internet.) A scientist named Suzanne Simard discovered it in 1997. She did an experiment where she covered up some trees in the forest so they couldn’t make nutrients from sunlight. Then she fed other trees a special kind of nutrient she could trace. When she tested the covered trees, she found they had some of the special nutrient, even though she hadn’t given it to them. The nearby trees had shared the nutrient with the covered trees!

The wood wide web is a busy place where signals zoom back and forth. The largest, busiest trees in the network are called mother trees or hub trees. Mother trees send the most signals, and they may be linked to hundreds of other trees. Mother trees also use the network to send extra nutrients to young saplings to help them grow big and strong.

However, like our own Internet, sometimes not everyone is nice on the wood wide web. Hyphae may pick a favorite kind of tree and ignore others. Some trees try to keep their neighbors from growing. But usually, the mushrooms and the trees help each other.

We don’t yet understand all the ways trees work together, but scientists are trying to figure it out. In 2019, one team mapped the underground networks of 28,000 tree species in more than 70 countries. Understanding how trees talk to each other could help us take better care of the Earth. Planting trees we know help each other grow next to each other could make forests healthier and stronger.

So, the next time you look at a group of trees, ask yourself, “What are they saying?”