About: Heterobasidion occidentale

Heterobasidion occidentale is a tree root-rotting pathogenic fungus in the family Bondarzewiaceae. It is endemic in western North America west of the Rocky Mountains from Alaska to southern Mexico. While a natural agent of forest turnover, H. occidentale has become of increased concern due to forest management processes such as pre-commercial thinning, altered site density and species composition, and carbon sequestration. H. occidentale forms part of the genus that includes other species forming the important forest pest Heterobasidion annosum sensu lato that is spread across the Northern Hemisphere. H. occidentale is part of the S-type intersterility group differing from the other North American species, Heterobasidion irregulare.