Above: Image © shazku,iStockPhoto.com

Imagine a forest full of trees. Each tree stands tall and solitary. It has its own trunk, branches and leaves.

But did you know that those trees are connected by a complex network hidden underground?

So what is this network made of? Fungi! Scientists believe almost all plant species worldwide are in relationships with fungi living in the soil. These fungi can connect the roots of different trees (and other plants) to create what’s called a mycorrhizal network.

A mycorrhizal networks can influence the survival, growth, health, and behaviour of the trees linked within it. Trees use their network to do such things as communicate and share resources. That’s why some scientists call it the internet of trees, or the “wood wide web.”

How does the fungal network work?

Many kinds of fungus have the majority of their bulk underground. In the soil, fungus grows in threads called hyphae. Together, all of these threads form a network called a mycelium. These threads can colonize (live among) the roots of trees and other plants.

Fungi and trees form a symbiotic relationship (a relationship they each benefit from). Trees produce food, in the form of sugar, through photosynthesis. They share this sugar with the fungus. Meanwhile, the fungus finds and absorbs nutrients from the soil to give back to the tree.

Did you know? Scientists think that about 90% of plant species form mycorrhizal relationships with fungi.

Resource Sharing

Fungi aren’t the only ones sharing resources with trees. Trees share resources with other trees, too! They use the fungal threads as transportation. For example, seedlings (young plants) can’t grow as quickly in the shade because they aren’t getting enough light for energy. Bigger trees can help them out by sharing nutrients via fungal threads.

Did you know? Fungal threads can interact with tree roots in two ways. In an ectomycorrhizal network, the fungal threads coat the root and the threads spread into the roots between cells. In an endomycorrhizal network, the fungal threads pierce the root and enter its cells.

Also, trees share in times of plenty and receive nutrients back in times of need. For instance, one study focused in on how the Douglas fir (a coniferous tree) can be connected to a paper birch (a deciduous tree). In the summer, when its leaves are out, the paper birch will have plenty of resources. So, it will give nutrients to the Douglas fir. In the winter, the paper birch no longer has leaves but the Douglas fir still has needles. So, the Douglas fir will reciprocate and provide nutrients to the paper birch.

However, some plants take advantage of the generosity of others without giving anything in return. For example, there are orchids that do not photosynthesize at all. Instead, they steal all their nutrients from nearby plants!

Defense

Disease and insect infestations can spread quickly throughout a forest - and they can be lethal for trees! Studies have found that trees can send help to their neighbours via the fungal network. For example, when a tree is attacked, it will release certain chemicals that travel through the fungal network and warn other trees of the danger. By having an early warning, other trees are better able to protect themselves.

One study has found that certain stressed and dying trees can even pass resources to their neighbours before they die. This gives the healthy receiver trees a boost in combatting the disease or outbreak.

Helping Relatives

Forests are made up of trees of different ages. The biggest, oldest trees are called mother trees. They are usually the trees that are the most connected in the fungal network. These mother trees nurture their offspring by providing them with the nutrients they need to prosper.

On the flip side, trees can use the network to stop the growth of unwanted neighbours. Some trees release toxic chemicals into the fungal network to slow down the growth of plants competing for their resources.

Forest Health

Trees rely on their fungal network to communicate and gain knowledge just as much as we humans rely on the internet! A healthy forest is one that is well-connected by the ‘internet of trees” and has plenty of mother trees. This allows a forest to recover from random changes, like those caused by humans harvesting trees.

Scientists can use what they’ve learned about the “wood wide web” to help loggers make better decisions when harvesting trees. For example, for reasons you’ve read about, loggers should keep mother trees alive in the forest. And they should allow dying trees to release their nutrients before they remove them.

Next time you stroll through the woods, think of all the communication happening just beneath you!

Learn more

Fungus (2017)
V. Ahmadjian, C.J. Alexopoulos & D. Moore, Encylopaedia Britannica

Plants talk to each other using an internet of fungus (2014)
N. Fleming, BBC

Socialism in soil? The importance of mycorrhizal fungal networks for facilitation in natural ecosystems (2009)
M.G.A. Van Der Heijden & T.R. Horton, Journal of Ecology 97

Beverly McClenaghan

I have always loved animals and nature. This led me to pursue an undergraduate degree in zoology at the University of Guelph followed by a Master’s degree at Trent University studying avian ecology and conservation. Currently, I am working for a conservation organization in St John’s, Newfoundland. I am working in policy and outreach, which is teaching me a lot about the economic, cultural, and social side of conservation as well as the biology of conservation. Outside of work, I am an avid birdwatcher, rock climber, and hiker. I love sharing my passion for nature with others!