Tree fungi are a diverse group of organisms that include molds, mildews, bracket fungi, and mushrooms growing on wood. These fungi are fundamental to the ecosystem, acting as decomposers that break down dead and decaying wood fiber. The question of whether they pose a risk to human health is complex, as the danger depends entirely on the specific fungal species and the route of exposure. While most fungi are harmless to humans, some can cause severe reactions or illness.
Direct Toxicity and Ingestion Risks
The most immediate and life-threatening risk associated with tree fungi comes from accidentally eating a poisonous mushroom growing on or near wood. Many fungi that decompose wood, known as saprotrophs, produce fruiting bodies that contain highly toxic compounds. For example, the Death Cap mushroom (Amanita phalloides), responsible for the majority of fatal mushroom poisonings worldwide, often grows near tree roots and contains amatoxins that can fatally damage the liver and kidneys.
Other dangerous species, such as the Deadly Galerina (Galerina marginata) and the Funeral Bell (Galerina autumnalis), grow directly on decaying wood and logs. These species also contain amatoxins and can be mistaken for edible varieties. Symptoms of amatoxin poisoning often have a delayed onset, appearing six to 24 hours after ingestion, which complicates medical treatment. The toxicity of these species is unaffected by cooking, highlighting the necessity of expert identification before consuming any wild mushroom.
Respiratory and Allergic Reactions to Spores
The most common way tree fungi affect the average person is through the release of airborne spores, which are microscopic reproductive units. Molds, mildews, and large bracket fungi, or polypores, produce and release massive quantities of these spores into the air, especially in dry, windy conditions or when disturbed. These spores are recognized as potent aeroallergens that can trigger or exacerbate respiratory conditions in sensitive individuals.
Exposure to these fungal particles is strongly associated with symptoms of allergic rhinitis, hay fever, and asthma. Common wood-dwelling molds, such as Aspergillus and Penicillium, are ubiquitous in the environment and their spores can lead to inflammation and allergic reactions in the lungs. In people with pre-existing conditions like asthma, sensitization to fungal spores can lead to more severe symptoms, a reduced lung function, and increased hospital admissions. Repeated inhalation of Aspergillus spores can even lead to Allergic Bronchopulmonary Aspergillosis.
Fungal Infections (Mycoses)
A less common but more direct health concern is the possibility of certain fungi infecting human tissue, a condition known as mycosis. This risk is generally low for healthy individuals with intact immune systems. However, certain fungi found in the environment, particularly decaying wood and plant debris, can cause a localized infection if they enter the body through a break in the skin.
A well-documented example is Sporotrichosis, sometimes called Rose Gardener’s Disease, caused by the Sporothrix fungus. This fungus resides on plants, soil, and decaying organic matter, including wood. Infection typically occurs when a person is scratched or punctured by a contaminated thorn, splinter, or debris, allowing the fungus to be traumatically inoculated into the skin. The infection usually starts as a small, painless bump that can eventually ulcerate and may spread along the lymphatic vessels; systemic or disseminated sporotrichosis is extremely rare, usually only occurring in individuals who are severely immunocompromised.
Safe Handling and Removal Practices
The presence of tree fungi often indicates structural decay in a tree, which can create a hazard from falling branches or a collapsing trunk. To manage the risks posed by both the fungi and the weakened wood, safety and prevention are the most effective measures. When handling large quantities of decaying wood, mulch, or visible fungi, wearing personal protective equipment is advisable.
A well-fitted dust mask, such as an N95 respirator, can reduce the inhalation of airborne spores, which is particularly important for individuals with allergies or asthma. Gloves should always be worn to prevent the inoculation of fungi like Sporothrix through cuts, scrapes, or splinters. Never attempt to consume any wild mushroom growing on wood without expert certainty of its identification. If fungi are causing widespread growth near a home or if a tree’s structural integrity is in question, consult a certified arborist or a mycologist for professional evaluation and advice.