I Have Mushrooms Growing on My Tree and It Looks Decayed!

The reason I hate getting calls like this is because it often means a big tree is in trouble. As an established city, Davison is home to many mature oak, maple and locust trees. The more mature a tree is, the more likely it is that some type of fungus can find a way to penetrate a trees’ defenses.

Why Do Fungi Feed on Trees?

It all comes down to the sugar. Just like all living organisms, fungi require carbon, hydrogen, and oxygen for fuel and building materials. When we consume carbohydrates, our bodies break down the sugar molecules, extracting carbon, hydrogen, and oxygen to fuel our activities. Even cars rely on hydrocarbons, which are essentially a mix of carbon, hydrogen, and oxygen.

Similarly, trees consist of carbon, water, and oxygen, all arranged into complex molecules that form structural wood. The backbone of a tree is made up of cellulose, a long chain of sugars, and lignin, which binds and strengthens the cellulose.

How Do Fungi Feed on Trees?

Fungi break down the tree’s complex molecules using special enzymes. They reorganize these molecules to create and sustain their own structures, which grow as long, interconnected threads known as mycelium.

When mature, basidiomycete fungi produce fruiting bodies (mushrooms), which contain spores. When the temperature and humidity are right, the spores are released into the air to spread. The mushroom itself is just a small part of the entire fungal organism—much like an apple on a tree is a small part of the whole tree.

Can Trees Defend Themselves Against Fungi?

Yes, I’ve seen many trees in Davison fight off many types of fungi, provided they’re healthy. The first line of defense is the tree’s bark, which prevents fungi from entering. However, damage to the bark—whether from storms, lawn maintenance equipment, or untrained tree workers using spikes to climb—can create entry points for decay.

Similarly, damage to branches from improper pruning cuts can also invite fungi. If the tree is healthy enough, it can compartmentalize the infected areas and block the fungus from spreading inside.

Mushrooms Growing on Your Tree

If you see mushrooms growing on your tree or near its roots, chances are they belong to a group of fungi called basidiomycetes, also known as "club fungi" because their spores are produced on club-shaped structures known as basidia. These fungi include saprophytes, parasites, saprophytic parasites, and beneficial fungi. Recognizing the type of fungi is crucial for assessing your tree’s health and safety, which is why a certified arborist should be consulted.

Saprophytes

These fungi break down dead plant material like leaves and wood, and usually cause little harm to living plants. They play an essential role in the global carbon cycle and the health of the soil. However, saprophytes can enter trees through wounds, feeding on the dead wood (heartwood) inside the tree. While they cause decay, they don’t typically affect the living wood of a tree. In some cases, a tree may appear hollow yet still be structurally sound, much like a hollow building that’s still safe to occupy.

Parasitic Fungi

Unlike saprophytes, parasitic fungi feed on the living parts of the tree, especially the cambium—the layer just beneath the bark that transports water and nutrients. This makes parasitic fungi highly damaging, as they can interfere with the tree’s vascular system, leading to decline and potentially death. Parasitic fungi often show no visible symptoms until the tree becomes structurally unstable and eventually fails.

Saprophytic Parasites

These fungi start as saprophytes, feeding on dead material, but can become parasitic if the conditions are right. One dangerous example is Ganoderma sessile, which can cause serious structural damage by attacking both dead heartwood and living wood. These fungi often announce their presence with large polypore mushrooms at the tree’s base.

Beneficial Fungi

Mycorrhizal fungi are beneficial for trees, forming a symbiotic relationship with plant roots. These fungi attach to roots, extending into the soil to collect nutrients the tree needs. In exchange, the tree provides carbohydrates to the fungi. This mutual relationship benefits both the tree and the fungi. Occasionally, you might see mushrooms from these fungi growing near the tree’s roots. While not all mycorrhizal fungi produce mushrooms, their presence is a good sign for the tree’s health.

What to Do if You Suspect Fungi in Your Tree

If you suspect fungal growth on your tree, it’s important to consult a certified arborist who is trained in identifying and assessing fungal risks. They may use tools like the Resistograph Decay Detection Tool to measure the extent of decay in your tree. Just because you see a fungus on your tree doesn’t mean it needs to be removed. There are many ways to improve a tree’s health and reduce risks, often saving the tree and lowering costs compared to tree removal.

Trees provide the Davison community with countless benefits, from oxygen to shade. Keeping them healthy not only improves the environment but also adds value to your property.