Ungulate foraging areas on seasonal rangeland in northeastern Oregon

Abstract

In much of the west, seasonal rangeland provides important foraging opportunities for wild and domestic ungulates during times when forage is often limited. We studied the use of foraging areas by Rocky Mountain elk (Cervus elaphus nelsonii Bailey), mule deer (Odocoileus hemionus hemionus Rafinesque), and cattle grazing the same seasonal rangeland in northeastern Oregon. We determined the potential for ungulate use to overlap and the influence of vegetation and terrain features on that use. Vegetation and terrain features of plant communities in the Festuca-Agropyron and Agropyron-Poa Associations were inventoried on a 1,844 ha study area of privately owned seasonal rangeland to define characteristics of ungulate foraging areas. Slope, aspect, elevation and, edge between bunchgrass and forested vegetation types, were evaluated from topographic quadrats. Observations of ungulate distribution on the study area were also obtained. A Geographical Information System using map overlays intersected spatially defined plant communities and terrain features with location of ungulates. Indices of ungulate preference for plant communities and terrain features were established. Discriminant analysis was used to determine which features were most likely to influence ungulate selection of foraging areas. Terrain features having greatest influence on ungulate selection of foraging areas were, distance to the ecotonal edge between steppe and forest communities, and elevation. Cattle preferred foraging areas comprised of Idaho fescue-annual grass plant communities located at medium distance from the forest edge and on moderate elevation. Elk preferred foraging areas comprised of bluebunch wheatgrass-annual grass and Idaho fescue-bluebunch wheatgrass near the forest edge at higher elevations. Mule deer preferred buckwheat-bluegrass scabland plant communities at medium distance from the forest edge at higher elevation. Probability of ungulates using similar foraging areas was highest for elk and cattle and least for elk and mule deer.