Extent of decay associated with Fomes igniarius sporophores in Colorado Aspen

The most destructive decay of aspen (Populus tremuloides Michx.) is caused by Fomes igniarius var. populinus (Neu.) Camb. This fungus accounted for 59 percent of the decay found in a recent study of aspen in Colorado (5).2 It is almost impossible to find stands of any age that are not damaged to some degree by F. igniarius, and trees with advanced stages of decay usually bear numerous sporophores (2) or conks (Fig. 1).