The effects of habitat fragmentation by forestry and agriculture on the abundance of small mammals in the southern boreal mixedwood forest

Abstract

To determine the effects of forest fragmentation on the abundance of small mammals, we livetrapped at edges and in the interior of forest patches in contiguous, logged, and agricultural landscapes in the southern boreal mixedwood forest of Saskatchewan. From 1994 to 1996, we captured 1548 small mammals (11 species) during 8172 trap-nights. The abundance of all small mammals combined was lower in forest patches isolated by logging than in contiguous forest or farm woodlots surrounded by agricultural land. This pattern was consistent in all years, despite significant annual fluctuations in numbers of the boreal red-backed vole (Clethrionomys gapperi), one of the most abundant species in our study area. Red squirrels (Tamiasciurus hudsonicus) and northern flying squirrels (Glaucomys sabrinus) were more abundant in farm woodlots. The abundance of deer mice (Peromyscus maniculatus) was significantly lower in forest patches surrounded by clearcuts, and we speculate that they may have used clearcuts more than forest patches. In contrast, the numbers of boreal red-backed voles were similar among landscapes. The only species showing a response to edge was the deer mouse, which was significantly more abundant at edges of farm woodlots than in interiors. We also found no significant difference in abundance of any species between small (10 ha) and large (>>20 ha) farm woodlots. For most species, within-landscape attributes such as edge and patch size seemed to have little effect on their abundance. However, for a variety of reasons, small-mammal numbers seem to vary considerably among forest patches in different landscapes.