SNOW AVALANCHES AND VEGETATION PATTERN IN CASCADE-CANYON, GRAND-TETON-NATIONAL-PARK, WYOMING, USA

Snow avalanches in Cascade Canyon, Grand Teton National Park, have a s ignificant effect on the region's vegetation mosaic, increasing the ar ea's community diversity and creating a fragmented vegetation pattern. The structure and persistence of communities within avalanche tracks is a function of the frequency of avalanche occurrence. In many areas, shrub cover and conifer density increase as avalanche frequency incre ases. Conifers decrease in size yet increase in age as avalanches occu r more often, a consequence of slower growth rates in trees within ava lanche tracks. Because the probability of avalanche damage to conifers is related to the size of the tree, slow growth rates result in small trees that can survive many years in avalanche tracks, contributing t o the persistence of the avalanche community. The canyon's vegetation patterns appear fairly stable due to the spatial and temporal consiste ncy of avalanche occurrence and the persistence of communities in aval anche tracks. The primary effect avalanches have on this landscape is to increase the fragmentation of the vegetation patterns rather than t o drive dynamic changes in the landscape mosaic.