Abstract:
Forest floor vertebrate species presence and abundance may be influenced by the volume and cover of coarse woody debris (CWD) in managed forests. I studied macro- and microhabitat associations of vertebrate species in 18 closed-canopy stands ranging in CWD volume from 14 to 859 m3/ha. Pitfall traps were used to capture small mammals and amphibians in spring and fall 1996 and spring
1997. Timed, area-constrained ground searches also were used to sample amphibians in spring 1996 and 1997. In general, macrohabitat associations indicated amphibian captures increased with CWD volume (m3/ha) but small mammal captures did not increase with CWD volume. Capture rates (#/1,000 trap nights) of Trowbridge's shrew
(Sorex trowbridgii were positively associated with fern cover and small diameter
log cover (< 50 cm diameter) and negatively associated with moss cover. Fog shrew (Sorex sonomae) capture rates were positively associated with herb cover, with rate increases similar in thinned and unthinned stands, but lower overall capture rates in unthinned stands. Capture rates of shrew-moles (Neurotrichus gibbsil) were positively associated with woody plant cover and negatively associated with large diameter log cover (> 50 cm diameter). Ensatina (Ensatina eschscholtzii) capture rates were positively associated with total CWD volume and fern cover and negatively associated with grass cover. Ensatinas captured during timed, area-constrained ground searches were positively associated with total CWD volume and average live tree dbh (cm). Capture rates of rough-skinned
newts (Taricha granulosa) were positively associated with bare ground cover. Clouded salamanders (Aneides ferreus) captured during timed, area-constrained ground searches were positively associated with total CWD volume. In general, microhabitat associations indicated the odds of detecting
ensatina and Trowbridge's shrew presence increased with CWD cover; fog shrew detection was not related to CWD cover. The presence of Trowbridge's shrew was negatively associated with moss and fern cover and positively associated with woody plant and small diameter log cover. Fog shrew presence was positively associated with herb cover. Ensatina presence was positively associated with fern and large diameter log cover and negatively associated with herb and twig cover. On average, amphibians captured during timed, area-constrained ground searches were 0.5 m from the nearest CWD, compared with 1 m between random points and the nearest CWD. My results suggest that current minimum guidelines and regulations for leaving CWD after harvest for state, private, and federal forest lands in western Oregon may not provide adequate habitat for some forest floor vertebrates, particularly terrestrial amphibians. Future research may provide
additional information to evaluate minimum CWD retention guidelines for other species.
