Interaction among cervids, fungi, and aspen in northwest Wyoming

Eighty-five 0.02-ha plots in the Gros Ventre River drainage of northwestern Wyoming with high elk usage had 39 % fewer aspen stems in 1985 than in 197 0. Sixty-five of these plots were remeasured in 1989 and 53 additional plot s established in 1986 on the Hoback River drainage (lower winter elk usage) were remeasured in 1990. Overall mortality (average/year) of aspen stems > 2.5 cm d.b.h. was 2.6% (1970-1985), 2.4% (1985-1989), and 2.3% (1989-1999) for the Gros Ventre plots, and 7.9% (1986-1990) for the Hoback plots. Large r stems (> 15 cm) had lower mortality rates than smaller stems. Additional studies conducted near elk feed grounds also showed that mortality caused b y pathogenic fungi was correlated with the amount of prior cervid injury to stem boles. Aspen sprouts exposed to cervids rarely exceeded I m in height . These observations indicate that herbivory and disease may be reducing as pen distribution in these ecosystems.