Root disease and exotic ecosystems: implications for long-term site productivity
Root disease fungi, particularly root-rotting Basidiomycetes, are key drivers of forest ecosystems. These fungi have co?evolved with their hosts in various forest ecosystems and are in various states of equilibrium with them. Management activities and various land uses have taken place in recent times that have dramatically altered edaphic and environmental conditions under which forest tree species and ecosystems have evolved. For example, in Sequoia giganteun stands, fire suppression in this fire-dependent ecosystem has resulted in increased mortality due to Heterobasidion annosum. On [One] hypothesis is that fire suppression results in increased encroachment of true firs, readily infected by S group H. annosum, thereby transferring the disease via root contacts with S. giganteum. Also, the existence of a hybrid between the S and P ISG's of H. annosum may be evidence for anthropogenic influences on evolutionary pathways in this pathogen. In other ecosystems, such as Pinus palustris (longleaf pine) in the Southeastern United States, increased mortality following prescribed fire is being observed. Various Leptographium species and H. annosum have been associated with this motility following relatively cool temperature fires, but how these fungi interact with fire and various edaphic factors are not known. Past agricultural practices that resulted in extensive soil erosion may have given rise to an "exotic ecosystem" in which longleaf pine is now maladapted.