DYNAMICS OF A SMALL MAMMAL COMMUNITY IN A FRAGMENTED FOREST

Community structure [species richness (S) and numbers of individuals captured] of a small mammal community were studied in July and August, 1987-1989, on a 1166-ha forested area in central Pennsylvania, which was divided into reference and treated sectors of comparable size. The reference sector was uncut, whereas the treated sector contained two areas with 50% and 75% fragmentation, respectively, resulting from forest clear-cutting in winter 1985-1986 and 1986-1987. I examined whether community structure of small mammals differed among years (1987-1989) or among forested areas that varied in extent of fragmentation. In addition, I compared community structure in 1987-1989 to that obtained on the same study site in 1982-1984 when extent of forest fragmentation was considerably less (25% and 50%) on the treated sector. Four-hundred nine individuals of seven species were captured during 4500 trap nights in 1987-1989, including white-footed mice (Peromyscus leucopus) (67.3% of total individuals), southern red-backed voles (Clethrionomys gapperi) (13.3%), and masked shrews (Sorex cinereus) (12.0%). Numbers of individuals captured of all species combined and of the three common species were significantly (P < 0.05) lower in 1988 than in 1987 and 1989, which I attributed to a drought in 1988 that presumably reduced the availability of terrestrial arthropods as a food resource. Although S was similar in 1987-1989 among areas of forest fragmentation and between 1982-1984 and 1987-1989, numbers of P. leucopus and C. gapperi captured were significantly (P < 0.05) higher in 1987-1989, especially in the area with 75% fragmentation. Numbers of P. leucopus were greater in 1987-1989 than in 1982-1984, perhaps because of a greater variety of microenvironments created by clear-cutting and increased availability of mast (acorns of oaks [Quercus] spp.) in 1987-1989. Numbers of C. gapperi likely were higher in 1987-1989 than in 1982-1984 because of moist microenvironments resulting from abundant low vegetation in clear-cut plots on the treated sector. I conclude that forests fragmented into small, even-aged plots can benefit P. leucopus and C. gapperi by increasing abundance of these two species.