Mycorrhizal network sustains diversity in a forest by transporting nutrients and water.

Introduction

In a Douglas-fir and pine forest in North America there are trees of all ages, ranging from tiny seedlings to giants that are hundreds of years old. Hidden in the soil is a vast network made up of millions of miles of thin threads called mycelium. Most of the mycelium spread throughout this forest are mycorrhizal fungi. These are fungi that live in a mutualistic partnership with trees and other plants.

The mycelium acts like an internet network but instead of moving electronic information around, they transport water and chemicals to keep the trees alive and communicating with each other. This network has been called the “Wood Wide Web”.

Image: Tobi Kellner / CC BY SA ‑ Creative Commons Attribution + ShareAlike

This image shows the fine threads of the mycelium from an oyster mushroom that serve as "fiber optic" connections in the Wood Wide Web.

The top‐down view of fungi and 67 Douglas‐fir trees in a 30×30 m plot. Green shapes are trees, sized relative to each tree’s diameter). Lines illustrate the linkages between tree roots through the fungal network. An arrow points to the most highly connected tree, which was linked to 47 other trees.

The Strategy

On the internet, nodes are individual computers and the network moves information among them. Hubs are places that connect lots of nodes together and have a lot of information traveling through them, such as Google. The nodes of the Wood Wide Web are all the individual trees in the forest. The oldest trees, which are often also the tallest and largest, are the ‘hubs’ because they have the most connections running through them.

Mycelia form the connections between all the nodes in the Wood Wide Web. The mycelia wrap around the fine roots of the hub tree and other vegetation, snuggling so close that water, nutrients, and other chemicals can move between the cells of the roots and fungi. A hub tree has more access to sunlight than smaller trees because of its size. Sometimes that results in it producing too much sugar through . When this happens, it sends the sugar out through the mycelium network to be used by its own seedlings and even other species of trees. The fungi take some of the sugar as it passes between trees and use it for themselves.

Water is also shared among the fungi and plants in the network. The water and nutrients increase seedling growth and help other trees survive. At another time, if the hub tree is stressed and needs water or nutrients, the mycelium and other trees can send them back to the hub tree.

Image: Atrebe10 / CC BY SA ‑ Creative Commons Attribution + ShareAlike

This diagram illustrates how mycelium integrates with root structures, forming a mycorrhizal relationship.

But this isn’t just about one hub tree. It’s about a hub tree connected to a seedling connected to a sapling, connected to another hub tree, and so on. Researchers at a study site in Canada discovered that one tree was connected to 47 others through this network. Sixty percent of the tree species in the world are associated with these mycorrhizal fungi. Most trees form symbioses with a wide variety of fungal species (there are more than 5000 of them) and each species of fungus can have relationships with a wide variety of trees.

Besides sharing nutrients and water, the network also sends warnings. If a tree is attacked by a bark beetle, it sends out a chemical signal, called a defense signal. The mycelium passes this signal along to other nearby trees. When they get the signal, they reinforce their chemical defenses, which makes it easier for them to fight off an attack when it comes.

Mycelium: How trees secretly talk to each other.

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The Potential

The Wood Wide Web can show us the value of sharing resources, efficient ways to move them, and the importance of forming close partnerships. We also can learn how to better manage our forests to maintain this underground network that provides mutual support to all partners.

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Last Updated November 3, 2020