Riparian and Upland Small Mammals on the East Slope of the Cascade Range, Washington

Abstract

Differences in small mammal diversity and abundance between riparian and upland areas have not been consistently shown in the Pacific Northwest, and the issue is expected to be complex along the east slope of the Cascade Range with its complex bio geography and forest landscape structure. The information is important for evaluating buffer zone management and the potential impacts of fuel reduction projects. We quantified small mammal species’ abundances, diversity, and indicator species in riparian and upland forest along three third-order streams. Each location had a set of four 5 x 6 pitfall kill-trapping grids with 15 m spacing and the first grid row 5 m from the water. One site had an additional set of four grids. We trapped for two weeks during late June and early July during 1997 and 1998 for a total trap effort of 13,411 trap nights. We captured 1,104 individuals of 14 species. Insectivores were 69% and rodents 31% of the captures. Sorex trowbridgii was the most abundant species (54% of all captures). Peromyscus keeni and P. maniculatus combined dominated the rodent community with 43% of rodent captures. Species richness and individuals captured generally were highest within 20-35 m of the stream. Sorex palustris, P. keeni, Microtus longicaudus, S. vagrans, and Zapus princeps showed strong affinities to the immediate riparian zone ( <5 m from the stream). No species were indicators or most abundant in the upland forest away from the riparian areas. Refuge and corridor functions for small mammals in riparian areas would be maintained by current buffer-width standards of 60-100 m.