Effects of thinning on forest-floor vertebrates and analysis of habitat associations along ecological gradients in Oregon coastal Douglas-fir forests

Thinning has the potential to increase structural diversity of managed forests for wildlife. During 1994--1996, I conducted experimental and observational studies using pitfall trapping to assess short-term and potential long-term effects of thinning on abundance and reproduction of forest-floor vertebrates in Douglas-fir (Pseudotsuga menzeisii) forests of the Oregon Coast Range. Thinning had positive effects on relative abundances of creeping voles (Microtus oregoni) and Pacific jumping mice (Zapus trinotatus) in both the short term and the long term. In contrast, relative abundance of western red-backed salamanders ( Plethodon vehiculum) was lower in stands thinned 7--24 years previously than unthinned stands, suggesting potential negative effects of thinning in the long term. Relative abundance of western red-backed voles (Clethrionomys californicus) decreased within 2 years of thinning but was similar in stands thinned 7--24 years previously and unthinned stands. However, reproductive performance of western red-backed voles was higher in thinned than unthinned stands, suggesting potential positive effects of thinning on reproduction of the voles in the long term.; In 1994, I investigated the influences of ecological gradients on habitat associations of forest-floor vertebrates at microsite and stand scales in 12 Douglas-fir stands in the stem exclusion stage. I examined various gradients of microclimate, stand structure, plant community composition, and downed wood. Among the ecological gradients I examined, the highest number of species was influenced by red alder/herb-conifer/shrub gradient of community composition at both the microsite and stand scales. At the microsite scale, 7 species were associated with red alder/herb communities whereas only 2 species were associated with conifer/shrub communities. Red-alder patches with herb understory, therefore, have a potential role in maintaining biodiversity of forest-floor vertebrate communities in young Douglas-fir dominated stands. Furthermore, I found that habitat associations of 4 shrew species were generally consistent between the microsite and stand scales, whereas those of 3 rodent species were inconsistent between the 2 spatial scales. I hypothesized that this rodent-shrew dichotomy in habitat association occurring at the 2 spatial scales is a result of differences in their ability to explore habitats at multiple spatial scales.