Fungi Functions

Fungi are one of the most fascinating life forms on Earth—as well as one of the most important. They can be unicellular (like yeasts and molds) or multicellular (like mushrooms). They constitute their own taxonomical kingdom, unique to all other life forms, although they are more closely related to animals than plants.

Some of the most valuable fungi are those that form a symbiotic relationship with plants—especially trees. Fungi do not contain chlorophyll, so they cannot make their own food, which is why they have created a mutually beneficial bond with plants. They receive food (in the form of sugars) from plants and provide valuable services in return.

Fungi are vital for the existence of trees. They decompose dead leaves into compost— creating invaluable nitrogen in the process. Fungi absorb chemicals and pollutants such as heavy metals—thus protecting trees. They accumulate water, helping trees to survive droughts. They produce hormones that encourage new root tips, thereby controlling a tree's growth. Trees communicate with each other through their roots, using fungi to link them in shared networks (sometimes called the “wood wide web”).

In a healthy forest there is a wide variety of tree and fungi species, so they mix and match. If one species of fungus dies, trees will search for another species. Likewise, if a species of tree dies, fungi will search for another kind of tree to link to. When humans disturb a forest, these exquisitely balanced symbiotic relationships can become severed—harming both trees and fungi, and thus the health of the woods.

Underground fungal networks can be huge. They can span thousands of acres. The total length of mycelium (the stringy underground part of the fungus, containing fine white filaments) in the top few inches of forest soil is some 270 quadrillion miles (450 quadrillion km) long—which is about half the width of our galaxy! One forest fungi in Oregon is about 2400 years old and weighs over 600 tons! Some one-third to one-half of all the living mass in soils is fungi. That’s pretty heavy-duty importance!

So, why should we be aware of—let alone concerned with—the millions-of-years-old cooperative relationship between fungi and plants? To begin with, that relationship and its crucial importance to the health of the ecosystem is being threatened by human activity. If this symbiotic dependence is broken, neither trees nor fungi will fare well. They cannot thrive—or even survive—on their own.

How are we humans disturbing this delicate balance? When logging operations invade a forest, that symmetry is destroyed. Clear-cutting an area of trees isolates the fungi, which cannot exist alone. The remaining fungi and trees become ill. Monocropping destroys the balance between numerous kinds of fungi and plants. Some one-third to one-half of the living mass of healthy soils is fungi. By damaging either plants or the fungi, that balance is destroyed. 

One scientific projection estimates that, by 2050, more than 90% of the planet's soil will be degraded, if we don't change our ways. By focusing our attention on above-ground ecosystems, we are in danger of ignoring the below-ground role of fungi. We are upsetting a balance that has been established for 500 million years.

Healthy Tree Growth and Symbiosis with Others—Part 3

Over most of the world, parents—especially mothers—spawn babies and then watch over them, until they can fend for themselves. For some species—primarily those who create thousands of babies, such as fish—the mother deposits eggs and is gone when the offspring hatch. They’re on their own. For others, there may be a lengthy development phase, during which babies mature and learn how to survive. Human newborns require a decade or two before they are able to fend for themselves. Climax trees in a forest require even longer; a baby's dependency phase on its parents may last for several decades.

A mother tree may have numerous offspring sheltered on the forest floor beneath her, although she will hog some 97% of the sunlight, leaving a measly 3% to filter down to them. Under these low light conditions, they grow very slowly—but that's part of Nature's strategy, as they gradually prepare for full maturity. A baby tree's leaves are much larger than mom's, in order to capture as much of that wee bit of light as possible. Their trunks grow extremely slowly; creating bark that is tough and smooth, to ward off disease and insects.

Baby trees photosynthesize lots of sugar to foster their growth, but this also makes them scrumptious to herbivores. In Yellowstone National Park, elk became plentiful during the first part of the 20^th century, as wolves were killed off. Aspen and other species of trees suffered, as their saplings were mostly consumed. The reintroduction of wolves in the 1960s saw a reduction in the elk herds—allowing aspen and other tree babies a better chance to mature. The Yellowstone forest and streams are much healthier now.

When mother trees die and fall, the saplings—having waited all those years—are prepared and ready to quickly respond. A race for the sun ensues. The healthiest and fastest saplings succeed, while their less-robust siblings die. As they shoot for the sky, the straightest trees do best. They are balanced and can withstand winds better. Curved trees are less strong and resilient. Trees with forked trunks are weak and may split and then be susceptible to disease. These are Nature's ways of building healthy and vigorous forests.

Another aspect of a healthy forest is the symbiosis that occurs between trees and massive underground structures of different species of fungi. The fungus can be huge—up to several thousand years old and extending over thousands of acres. They are the largest living organisms in the world. Their relationship with trees is usually a case of mutual cooperation. Fungi provide water and nutrients to trees, ward off bacteria, and filter out harmful heavy metals. In response, trees feed sugar and various other carbohydrates to the fungi.

But the exchange is not always fully equal, as the fungi may emit hormones that induce a tree's growth to their advantage. Selfish fungi may even consume up to one-third of a tree's production of sugar from photosynthesis. That said, tree-fungi interdependence is just one example of Nature's web that maintains a flourishing forest.