Amphibians in Managed, Second-Growth Douglas-Fir Forests

Abstract

Few studies have been conducted on amphibian communities in managed, second-growth Douglas-fir (Pseudotsuga menziesii) forests in the Pacific Northwest. My objectives were to investigate patterns of amphibian species richness, biomass, and abundance, and explore habitat relationships in different age classes of second-growth Douglas-fir forests managed primarily for timber production. I sampled terrestrial amphibian populations occurring in 4 distinct age classes of managed forest in western Washington with pitfall traps from 1992 to 1994. Although these forests were devoid of residual old growth, and all stands were at least in their second rotation, they contained the same assemblage of amphibian species occurring in unmanaged Douglas-fir forests in this region. Terrestrial amphibian communities in managed forests were structured differently than in unmanaged forests, however, with higher proportions of northwestern salamanders (Ambystoma gracile) and western redback salamanders (Plethodon vehiculum), and a much lower proportion of tailed frogs (Ascaphus truei). Contrary to several previous studies, I found no evidence that variation in amphibian abundances was strongly influenced by the amount of coarse woody debris on the forest floor. Further research is needed to elucidate the effects of intensive timber management on coarse woody debris and its role in the persistence of terrestrial amphibian populations in managed forests. Because rotation-age stands (the oldest age class) had the highest amphibian species richness, total biomass, and total abundance, and contained significantly higher abundances of the ensatina (Ensatina eschscholtzii) and red-legged frog (Rana aurora) than all younger age classes, silvicultural strategies that increase the percentage of rotation-age forest conditions within managed landscapes are likely to enhance the long-term habitat quality of intensively managed forest landscapes for terrestrial amphibians.