Effects of thinning on small mammals in Oregon coastal forests

Thin trees within forest

A replicated, controlled, before-and-after study in 1994–1996 of four coniferous forest sites and a replicated, site comparison study in 1995–1996 of eight coniferous forest sites, all in Oregon, USA (Suzuki & Hayes 2003) found that thinning trees increased abundances of some small mammal species. Out of 12 species, abundances of three, deer mouse Peromyscus maniculatus, creeping vole Microtus oregoni and white-footed vole Arborimus albipes, increased in thinned plots during the two years post-thinning relative to in unthinned plots. Pacific jumping mouse Zapus trinotatus increased in thinned plots relative to in unthinned plots between the first and second years post-thinning. Seven species had similar abundances in each treatment. Western red-backed vole Clethrionomys californicus was less common in thinned than in unthinned plots. Capture rates did not significantly differ between plots before thinning. See paper for data. Of nine species, five, Pacific shrew Sorex pacificus, Trowbridge’s shrew Sorex trowbridgii, vagrant shrew Sorex vagrans, creeping vole and Pacific jumping mouse, were more abundant in plots thinned 7–24 years previously than in unthinned plots. See paper for data. Four sites, each with three 35–45-year-old Douglas-fir stands (26–40 ha/stand) were studied. Two stands/site were thinned in 1994–1995 (to averages of 193–267 trees/ha) and one was unthinned (average 500 trees/ha). Also, at eight pairs of stands, 52–100 years old and <1 mile apart, one stand (10–28 ha) had been thinned 7–24 years before surveying and one (20–73 ha) was unthinned. Small mammals were surveyed within the controlled study using pitfall traps for six weeks/year in 1994 (before thinning) and in 1995 and 1996 (after thinning). In the site comparison study, pitfall traps were operated for 40 consecutive days in each 1995 and 1996.

(Summarised by: Nick Littlewood)