Have you ever lifted a stump and found a white, furry, web-like structure clinging to the underside of the wood? I know I have, and I always wondered what this funny looking substance was. Well, it turns out it’s a part of a fungus—and it is more important to our ecosystems than I could have ever imagined.

What is mycelium?

Mycelium is the word we use to describe the parts of a fungus other than the mushroom. The mycelium is usually hidden from sight underneath soil or rotting logs. To put it simply, mycelium is like the root of a mushroom, but it would be offensive to the extraordinary fungi to stop its description there. Mycelium is the vegetative body of a fungus, A.K.A the part that does all the work. It hides below the soil or on other substrates and forms vast networks, and is also responsible for the fruiting body of the fungus, or what we know of as the “mushroom.” These networks of mycelium can be so small they are invisible to the naked eye, or as large as 10 square kilometres! It’s true, the largest organism on earth is a fungus that lives in Oregon.

What do fungi eat?

There are no grocery stores for fungi, and they can’t move around and hunt like a predator. So, how does an organism that is stuck in one spot like a plant, but cannot use energy directly from the sun, get its food? Here is where the mycelium comes in. Mycelium secretes enzymes to break down complex organic molecules from things like branches, leaves, dead bugs, animals, etc. into digestible nutrients that the mycelium can absorb and use to grow. Since few other organisms are adapted to use these food sources, this is a great strategy for getting energy. However, not all fungi make a living by breaking down things that are already dead. The different strategies fungi have adapted to acquire food have led them to form unique and surprising relationships with plants; relationships that shape the world around us in ways we are just beginning to understand.

What role does mycelium play in ecosystems?

Before we dive into the diverse role mycelium plays in our ecosystem, it is important to establish that there are three ways fungi obtain energy: parasitic, saprophytic, and mycorrhizal. Parasitic fungi require a living host to survive, stealing food from the host; saprophytic fungi live by breaking down dead organic matter and recycling nutrients; mycorrhizal fungi form a symbiotic relationship between the mycelium and the roots of host plants. It is this third way of getting food that is most fascinating and plays the most important role in forest ecosystems.

Marvelous mycorrhizae

Plants have something the fungi needs: energy from the sun in the form of sugar. The fungi on the other hand, has something the plant needs: access to the nutrients trapped in complex organic molecules. These nutrients are not available to the plant. So, like a small child who cannot open the cookie jar, the plants must bribe their fungal partners with sugar to open the jar and hand them a cookie (nutrients). This relationship plays an incredibly important role in our forests. Fungi do more than form connections with individual plants. The mycelial network of one individual fungus connects with many individual plants, forming a vast interconnected web of shared information and nutrients throughout the forest. Amazingly, mycorrhizal fungi can do more than just exchange energy and nutrients with the plants they are connected to, they can also act as a mediator between healthy and unhealthy individual plants, passing vital nutrients from the healthy to the weak. Mycorrhizal fungi are the communication and resource transportation infrastructure of the biological world. However, just as traffic accidents, storms, and earthquakes can interrupt and endanger our infrastructure, some human activities are threatening these highways beneath our feet.

Threats to mycelium

Imagine a highway—one that is the only connection between towns; the only route for emergency vehicles; and the only way to get resources from town A to town B. Now imagine an earthquake takes out this road. All traffic is stopped, emergency vehicles cannot get through, and resources run dry in the towns. The consequences would be life-threatening. Well, this is what can happen to our forest ecosystems when this delicate network is disrupted. Disruptions to mycelium can happen due to soil disturbance like tillage, digging, and compaction, while agricultural practices such as fertilizer and fungicide applications can kill mycelium. Soil disturbance can happen very easily and unfortunately, most of us contribute to it. Here on Mayne Island, we have a long history of logging. In fact, almost the entire island has been logged at least once. Heavy machinery use, stump removal, and compaction of soils all have detrimental effects on the fragile networks of mycelium in the forest, but perhaps the most significant is the loss of all vegetation. In the absence of vegetation mycelium starves and mycorrhizal life within the soil is wiped out. In addition, soil compaction from machinery during development can have unexpected impacts on nearby trees and other plants. Even our beautiful parks suffer from soil compaction as we tramp through the forests. So, if harming mycorrhizal networks is so easy to do, how can we decrease our impact and help our fungi friends?

Save the mycelium

We know some disturbance in inevitable, but with awareness, we can minimize how much disturbance we create. The first step is to take care of our trees. Whether it be leaving as many trees standing on your property as possible —particularly veteran trees—planting a diversity of tree species, or leaving dead and dying trees to decompose naturally, you can help maintain and support mycelium networks. Secondly, soil disturbance should be prevented as much as possible. This includes construction, farming/gardening, and even hiking. Limit heavy machinery use to designated areas, practice more regenerative forms of farming with less fertilizers and tilling and leave as much land natural as possible. When hiking, it is important to stay on the designated trails to avoid compacting the soils and creating alternate paths for more people to follow. Keep in mind when conserving natural areas on your property that what lies beneath the forest floor is as important as what you see above.

Additional Resources:

Mycorrhizal fungi: all you need to know about the Internet of Plants | by Dario Cortese | The Startup | Medium

This Underground Economy Exists in a Secret Fungi Kingdom – YouTube

Exploring How and Why Trees ‘Talk’ to Each Other – Yale E360


Geoff Chapman · August 23, 2023 at 5:17 am

Here in the UK and an ancient amatuer mycologist, I believe that I have the choice of clearing my lawn of most weeds particularly Dandelions without impacting the grass ,with a product called Weedol(could be others) OR ensure that a recent and very new productive showing of Boletus Edulus and family is not destroyed or damaged in future by me NOT applying any such product to resurrect the lawn to presentation standard. ie. Is the mycelium bound to be affected if I did.? Comments to my email address very welcome

    Rob Underhill · October 3, 2023 at 3:45 pm

    Hi Geoff,
    Recommend letting the fungi thrive and make that the new presentation standard!

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