Why Do Fungi Feed on Trees?

It all comes down to sugar. Like all living things, fungi need carbon, hydrogen, and oxygen to survive and build their structures. When we consume carbohydrates, our bodies break them down and use the carbon, hydrogen, and oxygen for energy or to build tissues. Even your car uses carbon, hydrogen, and oxygen through hydrocarbons. Trees are made of these elements too, which form complex molecules like cellulose and lignin. The tree’s structure is made up of cellulose, a long chain of sugars, and lignin, which binds the cellulose and gives the tree its strength.

How Do Fungi Feed on Trees?

Fungi use enzymes to break down these complex molecules, rearranging them to create their own structures, called mycelium. Mycelium is a network of long, threadlike cells that spread through the tree. When basidiomycete fungi mature, they produce fruiting bodies (mushrooms) that contain spores. When the right temperature and humidity conditions arise, the spores are released into the air. The mushroom is only a small part of the larger fungal organism, like an apple on a tree, with the mycelium representing the entire fungus.

Can Trees Defend Themselves Against Fungi?

Yes, trees can defend themselves if they are healthy and have enough resources. The bark is the first line of defense, as it prevents fungi from entering. Damage to the trunk from storms, construction equipment, or even untrained tree workers using spikes to climb a tree can create pathways for decay. Other common entry points include damage from storms, improper pruning, or root disruptions during development. If the tree is in good health, it can wall off fungi using a process called compartmentalization, which prevents the fungi from spreading throughout the tree.

Mushrooms Growing on Your Tree

If you notice mushrooms growing on your tree or around its base, they are likely part of the basidiomycete group of fungi. These fungi are often called "club fungi" because they produce spores on club-shaped structures called basidia. Within this group, there are saprophytes, parasites, saprophytic parasites, and beneficial fungi. Understanding these types is crucial when assessing your tree’s health, which is why it’s best to consult an ISA Certified Arborist that services the Swartz Creek area.

Saprophytes

Saprophytic fungi break down dead plant material like fallen leaves and rotting wood. These fungi are crucial for soil health and the global carbon cycle. Although they may enter a tree through a wound and feed on the heartwood (the dead part of the tree), they cannot harm the living tissue. It’s not unusual for a tree to be hollow and decayed inside but still structurally sound, much like a hollow building. An ISA Certified Arborist can help determine whether your tree is still stable despite internal decay.

Parasitic Fungi

Parasitic fungi feed on the living parts of a tree, specifically the cambium, the layer behind the bark responsible for transporting water and nutrients. This nutrient-rich area is an ideal place for fungi to thrive. Feeding on this layer can weaken the tree, causing it to decline, structurally fail, or even die. It’s also common for parasitic fungi to show no visible signs, such as mushrooms or dieback, until the tree fails structurally.

Saprophytic Parasites

Some fungi are primarily saprophytic but can switch to parasitic behavior. A dangerous and common example is Ganoderma sessile, which feeds on both living tissue and dead wood, causing potentially hazardous conditions. These fungi often reveal their presence with large polypore mushrooms growing at the base of the tree.

Beneficial Fungi

Mycorrhizal fungi are beneficial to trees and other plants. They form a symbiotic relationship with the plant roots by wrapping around them or even penetrating them. The fungi then grow into the soil to collect nutrients, which they exchange with the tree for carbohydrates. This mutually beneficial relationship promotes the health of both organisms. Occasionally, you might notice mushrooms sprouting near the roots, which is a positive sign for tree health, though not all mycorrhizal fungi produce mushrooms. Certified arborists often include these fungi in deep root fertilization mixes to improve soil conditions in urban areas, where mycorrhizae populations tend to be low.

What to Do if You Suspect Fungi in Your Tree?

If you think your tree has a fungus, consult an ISA Certified Arborist. These professionals are trained in identifying fungi and assessing the potential risks to your tree’s health and stability. Some arborists use tools like the Resistograph Decay Detection Tool to evaluate the extent of decay inside the tree. Just because a tree has fungi doesn’t mean it must be removed. Many options exist to improve the tree’s health and reduce risk, potentially saving the tree and often at a lower cost than removal.

Trees are valuable assets in Swartz Creek landscapes and to the environment in general, and the more we preserve them, the better for everyone. With the right care, trees can thrive despite the presence of fungi. If you notice fungal growth, contact an Owen Tree Service certified arborist for a proper assessment to ensure your tree remains safe and healthy.