Journal d'écosystème et d'écographie

Abstrait

Contrasts in Vegetation and Native Ungulate use

Natalia A. Brown* and Kathreen E Ruckstuhl

Cattle grazing can cause significant changes in quality and quantity of forage available to the wildlife. The effects of livestock on native ungulates are still unclear, and range from positive to negative depending on the season. The objectives of our study were to determine the impact of cattle grazing on the vegetation biomass and quality by comparing twenty-four livestock exclosures and corresponding grazed plots. Use of exclosures by bighorn sheep and elk were evaluated. Furthermore, we compared proportion of live vegetation and forbs from 1994-95 to 2005-06 to investigate long-term changes in the vegetation quality and biomass. As predicted, higher vegetation biomass and lower quality was found inside the exclosures during some of the months. The proportion of live vegetation found within an area was negatively correlated with acid detergent fiber (ADF) and positively correlated with crude protein indicating higher net energy and nutritional value. More forbs were found in the lightly grazed areas. Number of fecal groups did not differ significantly between exclosures and grazed plots. The number of sheep groups sighted was higher in grazed plots than exclosures during the summer, but not during the winter. The proportion of live vegetation and biomass did not change between 1994-95 and 2005-06, but more forbs were found in 2005-06 than before. Overall, most of our results corresponded well with previous studies. Care must be taken to ensure that nutritional requirements of native ungulates are met during the winter, as a decrease in vegetation biomass due to cattle grazing was more pronounced than the increase in quality during this time.