SCIURIDS IN PACIFIC-NORTHWEST MANAGED AND OLD-GROWTH FORESTS

An understanding of the factors governing sciurid abundance in the Pac ific Northwest is essential for prescribing forest management practice s for second-growth forests where recovery of Spotted Owl (Strix occid entalis) populations and enhancement of biodiversity are objectives. W e compared results of companion studies of sciurids in western Washing ton and Oregon and examined patterns of abundance in relation to habit at elements on the Olympic Peninsula to elucidate governing factors an d make recommendations for forest management. Regional contrasts show that Glaucomys sabrinus and Tamias townsendii in Douglas-fir forests i n Oregon are 4 times more abundant than in western hemlock forests in Washington, and dietaries of Glaucomys, and the fungal communities tha t provide its food, are more diverse in Oregon than in Washington. Gla ucomys sabrinus in old forests are 2 times more abundant than in young , managed forests without old-forest legacies (large live trees, large snags and large, decaying fallen trees); populations in young forests with old-forest legacies and with understory development may equal th ose in old growth. On the Olympic Peninsula, Glaucomys sakrinus abunda nce can be predicted by density of large snags and abundance of ericac eous shrubs. At least seven large snags/ha and well-distributed patche s of dense shrubs (cover within patches >24% and patches covering 40% of the total area) are necessary for high densities of Glaucomys sabri nus. Abundance of Tamias townsendii reflects size of dominant tree and well-developed understories. Abundance of Tamiasciurus douglasii seem s to reflect territoriality in concordance with food supply and was gr eatest where Glaucomys and Tamias were low in abundance. Patterns of a bundance of the sciurids in old- and managed forests suggests that sil vicultural manipulation of vegetation and creative snag or den-tree ma nagement could be used in a management strategy to accelerate the deve lopment of Spotted Owl habitat in areas where old growth is lacking.