Imagine that you are standing in the heart of an old-growth Douglas-fir forest. All around you, massive trunks soar skyward. You feel humbled and awed to be in the presence of such majestic, ancient trees. Yet below your feet, unnoticed, a secret network is growing, weaving its way through the tree roots. It is this network that makes the forest possible, and it is composed not of plants, but of fungi.
Fungi are often viewed in a negative light. After all, they can rot our food and our homes, causes illnesses (such as athlete’s foot and fungal meningitis), and destroy our crops. But hundreds of thousands of different species of fungi exist, and while some of them can be harmful, many are beneficial. We use yeasts, for example, in baking and brewing, and mushrooms (either grown commercially or gathered in the wild) are an important crop in some regions. Most often, however, fungi work quietly in the background, largely unnoticed except when mushrooms unexpectedly pop up in the middle of our yards during the night. Most fungi live on decaying plant material, helping to decompose it and return nutrients to the soil, where they can be used by future generations of plants and animals.
Although many people likely think of fungi as similar to plants, they are actually more closely related to animals. Fungi cannot produce their own food through photosynthesis (as plants do) but must obtain food from plants or animals, just as we do. A fungus begins its life as a spore, which is small, light, and easily carried by the wind. When a spore lands in the right spot (with the right food, moisture, and temperature), it begins to grow, producing hyphae, thin thread-like structures that form the “body” of most fungi. A mass of hyphae is called a mycelium, and this is the state that fungi exist in most of the time, although we rarely see it because it is typically embedded in soil, wood, or some other material.
The hyphae secrete chemicals to break down, digest, and absorb food from their surroundings (similarly to how we break down food in our stomachs and absorb it through our intestines). When the time is right (often in spring and fall, when the ground is moist and temperatures are moderate), the fungus produces its fruiting bodies, which bear the spores. These fruiting bodies, of which mushrooms are the most recognizable example, are what most people think of when they think of fungi, often not realizing that the individual mushroom is part of a much larger fungus, most of which is hidden below the ground. A fairy ring, for example, is produced by a single fungus. The mycelium has grown radially outward and died out in the centre, creating a ring over which the mushrooms grow. These rings may be hundreds of years old. The largest known living organism on earth is in fact a fungus, an Armillaria ostoyae fungus (a species that causes root rot in trees) that covers about four square miles of ground in Oregon and is several thousand years old. I wouldn’t be surprised to learn that even larger and older fungi exist elsewhere in the world, still undiscovered.
Although Armillaria can cause diseases in trees, there is another group of fungi growing in the soil that not only benefits trees and other plants, but is essential for their well-being and survival. This group is the mycorrhizae (from the Greek mýkēs, “fungus” and rhiza, “root”), a group of many different species of fungi, all of which form symbiotic relationships with plants. The fungal hyphae grow into the plant’s roots, supplying the plant with nutrients and water and helping to protect the plant from parasites and pathogens. Fungi are much better at absorbing nutrients than plant roots are, and this is especially helpful in regions such as the Pacific Northwest. Here, frequent rains leach nutrients out of the soil, leaving little for the trees and other plants. Only with the help of mycorrhizal fungi can the trees extract nutrients directly out of the organic humus layer above the soil. And of course, the fungi also benefit: they receive food (sugars) that the plant produces through photosynthesis.
The mycorrhizae also help to connect trees and other plants with one another (sometimes even with other species of plants), helping them to share nutrients. These mycorrhizal connections create what I called at the beginning of this post a “secret network” – a web of relationships between plants and fungi that is essential to the health of the forest but which is largely hidden from our eyes and unrecognized by most humans. Nearly all plants form relationships with mycorrhizal fungi; most will not grow well without them, and some (such as orchids) cannot grow at all without their fungal partners. The majestic Douglas-firs and western redcedars of the Pacific Northwest and the massive redwoods of California would not reach the sizes they do without the aid of fungi that are constantly growing below the surface, quietly working away and helping to create the forests we know. Without these fungal partnerships, the world as we know it would not exist.