Small Mammal Abundance on Native and Improved Foothill Ranges, Utah

Abstract

Small mammal populations were sampled annually over 4 years in native plant communities and improved rangeland types. Ail species of rodents were reiativeiy less abundant where western wheatgrass was the dominant vegetation, but other differences among types were specific to individual species. Due to speciesspecific habitat preferences, total rodent numbers were highest where both sagebrush and seeded vegetation occurred together, and total rodent biomass was slightly greater along this ecotone than in a pure sagebrush type. Small-scale type conversion projects designed to increase the diversity of seeded and native stands may maintain or increase rodent abundance where species with such dissimilar habitat requirements occur. Brush control and removal of sagebrush (Artemisiu spp.) and pinyon-juniper (Pinus-Juniperus) vegetation have been common practices on Intermountain Region rangelands. Estimates of the public lands treated in this area include some 1,330 km* of various sagebrush control practices in Utah and Idaho (Vale 1974) and 1,350 km2 of pinyon-juniper chainings of Utah (Aro 1975, Payne 1980). While these estimates represent a small portion of the public lands in this region, treatments applied in large blocks have substantially altered the composition and form of vegetation in localized areas (Vale 1974). Some wildlife managers have expressed reservations concerning the value of these range improvements for wildlife. Roberts (1975) generalized that the majority of native wildlife species are adapted to native plant communities and would not benefit from seedings of exotic grasses. Identification of animal species restricted to native vegetation and those with habitat requirements more compatable with these range improvements is then important in balancing wildlife needs with other resource uses. The large size, lack of interspersion of native and seeded types, and predominance of seeded monocultures in past conversion projects have also been criticized (International Association of Game, Fish, and Conservation Commissioners 1971, Vale 1974). Interspersion of seeded and native types in smaller units may alleviate some of these features perceived as undesirable. Treatments landscaped to increase the mixture of cover types may improve habitat for some species as an extension of classical principles of wildlife management (Urness 1978). This paper reports a portion of small mammal studies undertaken at the Tintic Valley Experimental Pastures in central Utah from 1978 through 1981. Our objectives were to compare the relative abundance of small mammals among the existing vegetation types and to provide baseline data for comparison following potential future manipulations.