The mushrooms you see on a woodland hike are like the tips of icebergs, heralding something much larger below. Some species of fungus boast networks beneath the soil that can extend for miles. These subterranean webs also play an outsize role in the forest ecosystem.
“It’s hard for us to imagine there are such large organisms under our feet,” says Anne Pringle, a mycologist on sabbatical at Harvard Forest, in central Massachusetts. “Fungi may be the largest creatures in the forest.”
THEIR OWN KINGDOM
Pringle’s use of the word “creature” is intentional. While scientists long classified fungi as plants, genetic studies have shown they are more closely related to animals.
Fungi do not make their own food through photosynthesis, as plants do, and most fungi have cell walls made of chitin, the same material that’s in the outer shells of insects. Fungi even make up their own kingdom in scientific classification.
LIKE APPLES OF A TREE
In their relationship to the rest of a fungus, “Mushrooms are just like the apples of an apple tree,” Pringle says. “They’re the reproductive structures, creating and dispersing spores to create more fungi.”
The subterranean, vegetative form of fungi, known as mycelium, is a mat of threadlike filaments, called hyphae. Just like the tree that outlives each year’s apples, the mycelium still operates underground after the mushrooms disappear.
RECYCLERS AND MUTUALISTS
Many fungi serve as the decomposers of the forest floor, breaking down plant and animal matter to recycle essential nutrients.
Mycorrhizal fungi grow in association with the roots of certain trees and other plants, forming a mutually beneficial relationship. The plant uses the mycelium’s vast web to absorb nutrients, including nitrogen and phosphorus, from the soil. In exchange, it provides sugars and starches that the fungus can’t produce on its own. Most plants, in our northeastern forests and around the world, rely on this fungal network. The relationship may help plants survive drought and resist disease.
A COTTONY WEB
If you carefully lift a rotting log and look closely at the soil beneath, you will find that the ground is teeming with hyphae, which look like white, black, or brown threads. These masses of strands, smaller than roots, resemble a web of cotton.
“You can see them everywhere if you know what you’re looking for,” Pringle says. Once you’ve seen the hyphae, she suggests carefully putting the log back as you found it.
For every species of plant on the planet, there are probably four to 10 species of fungi, Pringle says. Yet the fungi are not all known. “We have names for approximately 100,000 species, which we think is about 5 percent of the diversity,” she says.
Without a better understanding of all the fungi and how they function, whether in the forests we hike or in other ecosystems, it’s hard to know what we may be losing as they respond to changing conditions. That’s a problem Pringle thinks we should address. “In conservation biology and discussions of endangered species, people focus on plants and animals,” she says. “A dialogue on fungal diversity has hardly started.”