Diseases of Forest Trees: Consequences of Exotic Ecosystems?
Much attention is now given to risks and impacts of exotic pest introductions in forest ecosystems. This concern is for good reason because, once introduced, an exotic pathogen or insect encounters little resistance in the native plant population and can produce catastrophic losses in relatively short periods of time. Most native fungal pathogens of forest trees have co-evolved for eons with their hosts and have reached a sort of balance between them and populations of susceptible tree species. Recent studies on various forest types have indicated a higher incidence of certain fungal Pathogens than were previously thought to occur. These pathogens are either the type not normally thought of as highly virulent or are those that have not been previously reported as a serious problem on a particular host. For example, Pathogenic fungi belonging to both the Leptographium complex and Heferobasidion annosum, are associated with mortality afier prescribed burning in certain longleaf pine stands. Yet, this tree species has traditionally been rankd as highly tolerant to these fungi. Could these observations reflect some manifestation of "exotic ecosystems," whereby the conditions under which particular tree species evolved are no longer present or are altered in some way that increases their susceptibility to these fungi? With the current emphasis on ecosystem restoration and alternative silviculturel regimes, it is critical to address such questions in order to avert losses in forest productivity.