Estimating root disease losses in northern Rocky Mountain national forests

Abstract

Root disease losses were estimated on more than 3 million hectares of commercial forest land within seven national forests in the northern Rocky Mountains. Area estimates were made for root disease centers on all seven forests and scattered tree mortality on three forests. Tree mortality rate and associated volume loss were estimated for two forests. Approximately 31 600 ha (about 1% of the total commercial forest land) were occupied by large active disease centers discernable from large-scale aerial photographs on these forests. About 13% of the commercial forest land of three forests contained scattered root disease mortality of at least 3 trees/ha. About 35% of the annual tree mortality was associated with root diseases on two forests. Major root pathogens found were Armillariamellea and Phellinusweirii; bark beetles often infested root-diseased trees. Recommendations for improvement of survey techniques are discussed.