Fungi on Trees – An Arborists’ Field Guide
People involved in tree hazard assessment generally believe that it is important to identify any decay fungi that are found. Fungi identification is, however, sometimes rated too highly as a useful procedure, perhaps because there is a belief that is somehow tells us most of what we need to know about a tree in order to prescribe a course of management. There is perhaps even a false analogy with the diagnosis of disease in human beings. Decay is however, not a disease; it is normal consequence of aging and/or injury in trees, which releases mineral nutrients that have been locked up in their wood and provides habitats for other species. In fact hollowing is a perfectly natural occurrence and is seen as a co-evolutionary relationship between the tree, fungi, bacteria and other micro-organisms. Depending on the species of fungus and of the host tree, the two can often co-exist for centuries; sometimes even for millennia.
As far as the health of the tree is concerned, certain decay fungi can extend into sapwood, causing localised loss of function. There is of course the concern that decay sometimes weakens trees enough to cause mechanical failure. When trying to decide whether some form of remedial action is needed, identification of decay fungi can be helpful. In particular some fungi are more likely than others to extend into wood that is needed for mechanical support and/or for water-conduction. Even then, branches can occasionally be shed: not necessarily a problem for the tree but sometimes a problem for the safety of people and property.
Guy Watson/Ted Green