• Foraging Ecology of Bison in Aspen Boreal Habitats

      Hudson, R. J.; Frank, S. (Society for Range Management, 1987-01-01)
      Studies on several wild and domestic ungulates suggest that large grazers attain higher maximum forage intake rates but require relatively higher forage biomass to do so. In this study, forage intake rates and feeding times of North America's largest wild grazer, the bison (Bison bison), were related to forage biomass during summer and autumn in aspen boreal forest habitats. Irrespective of season, maximum feeding rates of 68 g/min declined by 50% as forage biomass was reduced to 780 kg/ha. This reduction was due primarily to smaller bite sizes. However, bison compensated by increasing cropping bite rates to more than 60 bites/min on heavily grazed swards. Grazing times increased from 9 h/day in summer to 11 h/day in autumn, offsetting slight decreases in average foraging efficiency. During summer, a greater proportion of grazing occurred at night. Upland meadows were preferred habitats for grazing despite relatively low pasture biomass and potential dry matter intake rates.
    • Shrub Litter Production in a Sagebrush-Steppe Ecosystem: Rodent Population Cycles as a Regulating Factor

      Parmenter, R. R.; Mesch, M. R.; MacMahon, MacMahon. J. A. (Society for Range Management, 1987-01-01)
      This study examines the impact of long-tailed vole (Microtus longicaudus) and deer mouse (Peromyscus maniculatus) population changes and their feeding behavior on shrub populations and the resulting litter production in a shrub-steppe ecosystem in southwestern Wyoming. Rodent populations were monitored on 3 replicate plots over a 3-yr period. Populations peaked in autumn 1983 and declined to lower levels in 1984-86. Damage to shrubs (in the form of bark-stripping and girdling) was observed after the winter of 1983-84, but not after the winters of 1984-85 and 1985-86. We assessed damage to shrubs on 4 sites. Extent of damage, mortality, and biomass-to-litter transformations were quantified. We found that: (1) 21% of all shrubs and 28% of the big sagebrush (Artemisia tridentata) sustained rodent damage; (2) 1% of all shrubs were killed as a result of girdling; (3) mean biomass lost from shrubs that suffered damage was 36%; (4) total aboveground biomass loss occurring on big sagebrush was 231 kg/ha or 4% of the standing crop. These results indicate that rodents feeding on big sagebrush can periodically increase annual rates of litter production by as much as 69% above "normal." Rodents in the sagebrush-steppe ultimately influence ecosystem-level nutrient cycles by accelerating shrub litter production, and may affect plant species composition via feeding-induced shrub mortality.