STAND-LEVEL PATTERNS AND ECOSYSTEM CONSEQUENCES OF BEACH BARK DISEASE

Synthesis of existing literature indicates that beech bark disease has direct and indirect effects on forest structure and function through the stand-level consequences of individual tree mortality. Tree-level factors known to influence disease severity include tree size, distance from pathogen source, topographical position, wind direction and speed, nitrogen concentration of bark tissue, and genetic resistance. When considering forested stands, tree-level factors must be combined with additional parameters to determine the effects of the disease on forest function. Additional stand-level controls on beech bark disease severity involve forest history, beech basal area, and forest composition. Aside from direct mortality attributed to disease, indirect mortality may arise from increased susceptibility of diseased trees to windthrow and ice storm damage. Combined direct and indirect mortality results in losses of larger American beech (Fagus grandifolia Ehrh.) stems, potentially increasing light availability for other tree species. However, large stem losses are balanced by prolific root sprouting in aftermath forests, which maintains dense stands of small beech stems that are effective resource competitors with economically valuable species. In addition to shifts in tree size classes, mortality also results in elevated amounts of coarse woody debris. Due to a paucity of baseline data from disease-free forests, it can be difficult to isolate the effects of beech bark disease relative to other forest processes in determining current forest structure and function. Research emphasis should be on monitoring key structural and functional attributes, such as coarse woody debris loads and nitrogen dynamics, in forests free of disease or those in the early stages of disease progression. Future research should also address the synergistic effects of beech bark disease and other major forest disturbances such as other introduced pathogens and windthrow