ELK, MULTIPLE FACTORS, AND PERSISTENCE OF WILLOWS IN NATIONAL PARKS

Managers are concerned over declines in willows (Salix spp.) and increasing elk (Cervus elaphus) populations in Rocky Mountain and Yellowstone national parks. We compare and contrast elk population trendsr elk herbivory rates on willows, willow growth ratest climates, and responses of willows to clipping. Both parks had similar patterns of elk densities (1 l-16 elk/km2), elk herbivory rates on willows (26-28% of current annual growth [CAG]), elk increases, long-term climate trends toward aridity, and recent wetter and cooler trends. Growth conditions for willows were better in Rocky Mountain National Park. Willow CAG was 250% greater, willow shoots were 100% heavier, and shoots were 41% longer in Rocky Mountain \lational Park compared to Yellowstone National Park (P 0.05). When previously protected willows were clipped (100%) over 3 years in Yellowstone National Park there was 250% less CAG, a 22% decline in height, andnoincrease in tannins or phenolics. Tanninsand phenolics increased in Rocky Mountain National Park. Elk had a greater negative effect on willows in Yellowstone National Park (P = 0.02)due to less suitable growth conditions for willow; i.e t precipitation was lower and there were fewer beaver pondscomparedto Rocky Mountain NationalPark. Abioticand biotic factors combined with elk densities affect willow physiologyt regenerationJ and persistence.