Abundances of Small Mammals in Fir Forests in Northeastern California

We compared abundances of seven species of forest rodents among three types of fir (Abies concolor and A. magnifica) forest: unlogged old-growth, unlogged mature, and shelterwood-logged old-growth. Small mammals were livetrapped during summers 1991 and 1992 in four grids within each type of forest; grids were located in the Lassen National Forest in northeastern California. Shelterwood-logged forests had been logged 6-7 years previously. Differences in capture rates between unlogged, old-growth and shelterwood-logged, old-growth forests suggest that logging led to significant increases in populations of goldenmantled ground squirrels (Spermophilus lateralis), yellow pine chipmunks (Tamias amoenus), and lodgepole chipmunks (Tamias speciosus) but may have led to reduced populations of western red-backed voles (Clethrionomys californicus). Capture rates of Douglas’ squirrels (Tamiasciurus douglasii), Allen’s chipmunks (Tamias senex), and deer mice (Peromyscus manicukatus) did not differ significantly between unlogged and shelterwood-logged forests. Capture rate of T. douglasii was significantly greater in mature forests than in oldgrowth forests in 1992, but we did not detect significant differences between old-growth and mature forests for the other six species. These results illustrate how opening of the canopy and disturbance of the forest floor can lead to significant changes in patterns of abundance of forest rodents.