Forest Stress: Influence of Air Pollutants on Disease Caused by Microbial Pathogens

Abnormal physiology, or disease, in woody plants follows infection and subsequent development of an extremely large number and diverse group of microorganisms internally or on the surface of tree parts. All stages of tree life cycles and all tree tissues and organs are subject, under appropriate environmental conditions, to impact by a heterogeneous group of microbial pathogens including viroids, viruses, mycoplasmas, bacteria, fungi, and nematodes. The influence of a specific disease on the health of an individual tree may range from innocuous to mild to severe. Over extended time periods, the interaction of native pathogens with natural forest ecosystems is significant, and frequently beneficial, in terms of ecosystem development and metabolism. As in the instance of insect interactions (Chapter 12), microbes, and the diseases they cause, play important roles in succession, species composition, density, competition, and productivity. In the short term, the effects of microbial pathogens may conflict with forest management objectives and assume a considerable economic or managerial as well as ecologic significance (Smith, 1970).