Impacts of Cattle Grazing on Mesic Grizzle Bear Habitat Along the East Front of the Rocky Mountains, Montana

Abstract

During the summers of 1985 and 1986, we measured vegetation characteristics to determine impacts of cattle grazing on cover and forage preferred by grizzlies within aspen and willow plant communities along the East Front of the Rocky Mountains in north-central Montana information collected on the phenology of bear foods growing in aspen and willow stands revealed that the more nutritious bear foods produced seeds late in the growing season. The utilization of bear foods by cattle in five study pastures showed that in 6 weeks all herbaceous bear foods were >40 percent utilized. Although sites protected from cattle grazing for 2 to 10 years had more aspen and willow suckers than did grazed sites, grazed sites appeared to be recruiting enough shoots for stand survival. Hiding cover for bears tended to be higher in ungrazed than grazed sites and in sites grazed in months other than June than in sites grazed in June. Deferring grazing in pastures with willow and aspen stands until 1 July and removing cattle from pastures when 50 percent of herbaceous forage in mesic communities was eaten would minimize short term impacts of cattle on plant species preferred by grizzlies. Long term management systems could be designed to encourage or discourage grizzly use of pastures by implementing livestock rotation systems that influenced seed production and standing crop of phenologically desirable growth stages of food plants and cover value of other plants.