Fungus has a role in a healthy forest ecosystem
Fungi help break down the materials in the stressed and dead trees as part of a complex nutrient cycle that is vital to regeneration and a healthy forested ecosystem.
Usually, when we see or hear news items regarding tree and forest fungus, it is being presented as bad or something that is killing trees. Sadly in many instances it’s true that newly introduced fungal pathogens, like Dutch elm disease and oak wilt for example, are a major issue resulting in the death of healthy trees.
The majority of fungi we find in the forest are beneficial to the overall health of the stands they are living with. It is inevitable that trees are going to get old, slowdown in growth and eventually die. These life cycle processes can be rather short in some species; for example aspen, jack pine and white birch or quite long stretching to over hundreds or even thousands of years in the longest growing species like northern white cedar in the Lake States region or sequoia and bristle cone pine in the west.
Regardless of how or when a tree dies, the process of decomposition begins. Tree cell walls contain lignin, a compound that strengthens the cells assisting trees to grow tall. Lignin is tough and fungi are thought to be the only major organism that can break it down. This is important to the remaining trees as well as for the newly established seedlings that depend on the nutrients in the dead and dying trees to allow them to grow and remain healthy. Without the decaying action of fungi, wood would not break down to supply the nutrients for the remaining stand in a timeframe that will sustain growth.
The process of plant growth, decline and decay followed by reabsorption of the released compounds is generally referred to as nutrient cycling. Although there are other organisms that aid in the breakdown of plant matter for this process, it is fungi that preforms the important first step by breaking down the lignin. These processes may be at work above ground in the tree stems and branches, or below ground in the roots and stumps. There are many different species and kinds of fungi that are at work in forest stands and vary depending on tree species, soil type and moisture conditions.
For a more detailed explanation of how the complex processes work to help sustain a healthy forest ecosystem Michigan State University Extension has a series of bulletins that covers this topic; Forest Terminology and Ecological Systems Extension Bulletin E-2635 through E-2641.