SMALL MAMMALS IN MANAGED, NATURALLY YOUNG, AND OLD-GROWTH FORESTS

Forest managers in the Pacific Northwest are faced with new challenges of providing for all wildlife in managed forests. Our objective was t o elucidate the factors governing the composition and biomass of fores t floor mammal communities that are amenable to management. We sampled small mammal communities in forests of various management histories o n the Olympic Peninsula and contrasted our results with those of other large studies in the Pacific Northwest. Forest floor mammal communiti es in forests >35 yr old in the Western Hemlock Zone of Washington and Oregon are composed of 5-8 characteristic species. These include Sore x trowbridgii (numerically the most dominant); one species each of Cle thrionomys, the Sorex vagrans complex, and Peromyscus; and Neurotrichu s gibbsii. Species composition changes from south to north, and the co mmunities on the Olympic Peninsula contain two or three additional spe cies compared to communities to the south. Communities in naturally re generated and clearcutting regenerated (managed) young forests are sim ilar in composition to those in old growth; old growth, however, suppo rts 1.5 times more individuals and biomass than managed forest. Commun ity diversity seems related to the south-north moisture-temperature gr adient that is reflected in increased diversity of canopy conifers, de velopment of forest floor litter layers, accumulation of coarse woody debris, and abundance of herbs, deciduous shrubs, and shade-tolerant s eedlings (as opposed to understories dominated by evergreen shrubs). P revious work found few habitat variables that were good predictors of species abundance in natural young and old-growth stands. Naturally re generated young stands had higher levels of coarse woody debris than o ld growth. Managed stands had much lower abundance of coarse woody deb ris and tall shrubs than old growth. Understory vegetation (herbs and shrubs) and coarse woody debris accounted for a major part of the vari ation in abundance of six of eight species in managed stands, but only two species in old growth. Management of Western Hemlock Zone forest for conservation of biodiversity and restoration of old-growth conditi ons should concentrate on providing multispecies canopies, coarse wood y debris, and well-developed understories.