Legacy retention versus thinning: Influences on small mammals

Management strategies for promoting late-seral attributes in second-growth forest need evaluation for their efficacy in maintaining biodiversity, including complete forest-floor, small-mammal communities. Two common strategies in the Pacific Northwest are (1) management with thinnings to promote large trees with developed understories and (2) retention of legacies, defined as live trees, logs, and snags from the preceding forest, at harvest, followed by protection but not thinnings of the new stand. We compared small-mammal communities resulting from >65 yr of application of these strategies in the Puget Trough, Washington. We also compared these communities with the small-mammal communities found in old-growth, naturally young, and extensively managed forests elsewhere in western Washington. Forests managed with thinnings had 1.5 times the individual mammals and 1.7 times the mammal biomass of forests managed with legacies of coarse woody debris and snags-differences similar to those between old-growth and naturally young forest (1.2 times more individuals in old-growth) and old-growth and extensively managed forest (1.6 times more individuals in old-growth). Management strategy had a profound impact on community structure, with the Columbian mouse (Peromyscus oreas), the small mammal mostassociated with old growth, much reduced in Puget Trough forests (absent from most stands) and the creeping vole (Microtus oregoni) (a species commonly associated with early seral stages, but found in all seral stages in Washington) third-ranked in thinned stands but seventh ranked in legacy stands. The montane shrew (Sorex monticolus) was second-ranked, after Trowbridge's shrew (S. trowbridgii), in marked contrast to codominance by the southern red-backed vole (Clethrionomys gapperi), S. monticolus, and P. oreas in old growth. Thus, neither strategy produced communities typical of late-seral forestsWilson and Carey "Legacy retention versus thinning: Influences on small mammals." Northwest Science. 2000; 74(2): 131-14