Carbon and nitrogen dynamics in elk winter ranges

Recent increases in elk (Cervus elaphus L.) herbivory and changes In hydrol ogy towards drier conditions have contributed to declines in willow (Salix spp. L.) communities in the winter ranges for elk in Rocky Mountain Nationa l Park, In 1994, we constructed 12 large elk exclosures in 2 watersheds of the winter range for elk in the park, and conducted field experiments from 1995 to 1999 to investigate the effects of herbivory and proximity to surfa ce water on the dynamics of C and N. Litterfall biomass averaged 65.6 and 3 3.0 g m(-2) inside and outside the exclosures, respectively. Elk herbivory increased (P < 0.05) N concentration of willow litter from 1.25 to 1.49%, b ut there were no differences in losses of C and N from litterbags placed in grazed and ungrazed plots in any of the growing seasons, Carbon losses fro m litterbags were higher in lower landscape positions (P = 0.001), in compa rison to upper landscape positions, Shoot biomass of willow plants fertiliz ed with N averaged 27.3 g and was higher (P < 0.05) than that of unfertiliz ed plants, which averaged 20.2 g, indicating that N availability limits pla nt growth in our study sites. Elk herbivory had no effect on soil inorganic N availability, even though H;e estimated that the return of N to the soil in grazed plots could be as much as 265 % of the N return in exclosed plot s. In the long-term, greater return of N to the soil combined with increase d litter quality in the grazed plots could contribute to increases in N cyc ling rates and availability, and these changes could affect ecosystem struc ture and function in the winter range for elh in Rocky Mountain National Pa rk.