Fungi are a diverse group of organisms that cannot produce their own food, absorbing nutrients from their environment. They are found in soil, water, or form parasitic or symbiotic relationships with plants or animals. On trees, fungi appear in various forms; some indicate health issues, while many play important ecological roles.
Common Types of Fungi on Trees
Visually distinct forms of fungi grow on trees. Bracket fungi, also known as shelf fungi or conks, are common examples. These fungi grow as woody, leathery, or fleshy projections that extend horizontally from the tree trunk or branches. They often have pores on their underside for spore release and can range from small to large, multi-tiered structures, sometimes exceeding 40 cm and developing annual growth rings.
Mushrooms, with their cap-and-stem structures, are another type of fungal fruiting body found on trees or near their bases. These vary widely in color, size, and shape; some grow directly from wood, while others emerge from the soil connected to tree roots.
Crust fungi appear as flat, paint-like patches on the surface of wood. Their spore-bearing surface can be smooth, wrinkled, warty, or toothed, often covering the undersides of fallen branches or logs. These visible forms represent only a portion of the fungal organism, with much of its body existing as a network of thread-like filaments within the wood or soil.
The Diverse Relationships Between Fungi and Trees
Fungi engage in various ecological relationships with trees, each with different implications for tree health. Saprophytic fungi are decomposers that obtain nutrients from dead organic matter.
These fungi play an important role in forest ecosystems by breaking down dead wood, leaves, and other debris, returning essential nutrients to the soil. Many bracket fungi and crust fungi are saprophytic, consuming the wood of dead trees or fallen branches, contributing to nutrient cycling.
Parasitic fungi, in contrast, infect living trees and can cause disease or decay. They enter trees through wounds in the bark caused by pruning, weather, or mechanical damage. Examples include fungi that cause cankers, which are sunken, dead areas on the bark, or wood rot that weakens the tree’s internal structure. Powdery mildew, which forms a white or gray film on leaves, is another common parasitic fungal disease. These infections can compromise a tree’s health and stability.
Symbiotic fungi, particularly mycorrhizal fungi, form mutually beneficial relationships with trees. The term “mycorrhiza” literally means “fungus root,” describing the close association between these fungi and tree root systems. The fungal network extends into the soil, increasing the tree’s ability to absorb water and nutrients like phosphorus and nitrogen. In return, the tree provides the fungi with sugars produced through photosynthesis. While these fungi are essential for tree health, their primary growth is usually underground and not visible on the tree’s surface.
Recognizing Concerning Fungal Growth
Observing certain signs on a tree can indicate that fungal growth might be problematic, suggesting potential tree health decline. The appearance of fruiting bodies, such as conks or mushrooms, directly on the main trunk or large branches, particularly at the base, can be a warning sign. While some fungi on dead wood are harmless, those emerging from living parts of the tree, especially the main stem, often suggest internal decay or disease.
Symptoms of tree decline associated with fungal infection include sudden branch dieback or a noticeable thinning of the tree’s canopy. Discolored or wilting leaves, or leaves with unusual spots, may indicate fungal disease. Soft or crumbling wood, particularly near the base or on large branches, indicates internal decay caused by fungi. Cankers, which are sunken or discolored areas on the bark that may ooze sap, indicate fungal infection. An overall weakening or leaning of the tree, combined with these fungal signs, signals structural concern.
Addressing Fungal Growth on Trees
Addressing fungal growth on trees involves a combination of prevention, careful observation, and professional intervention when necessary. Good general tree health is an important preventive measure. Proper watering, especially deep and infrequent watering, reduces moisture on leaves and around the trunk, discouraging fungal growth. Applying breathable mulch around the tree’s base retains soil moisture and regulates temperature; keep it away from direct trunk contact. Avoiding bark damage and proper pruning, like removing dead or diseased branches to improve air circulation, also contribute to prevention.
Many saprophytic fungi on dead wood or stumps do not harm living trees and require no intervention. However, if fungal growth appears on living tree parts or decline symptoms are observed, close monitoring is advised. Regular inspection for early signs like discolored leaves, unusual growths, or bark changes allows for timely action.
For significant fungal issues, especially on large trees or those showing structural instability, consulting a certified arborist is recommended. Arborists can diagnose the fungus and damage extent, offering appropriate treatment. They also guide on safety risks and removal necessity. Attempting to remove certain fungal growths, like conks, without professional advice can inadvertently release billions of spores, potentially spreading infection.