Depauperate Small Mammal Communities in Managed Pine Plantations in Eastern Virginia

Abstract

Loblolly pine (Pinus taeda L.) plantations of four different ages were examined to identify changes in the small mammal community in relation to changes in the vegetational community. Small mammals were evaluated during five seasons using two methods of trapping. Live traps accounted for 65% of captures and seven of nine species, whereas pitfall traps yielded eight species, of which two were not taken with live traps. For both trap types, catch rates averaged less than two per 100 trap-nights, very low even for pine forests. Both abundance and biomass of small mammals declined with increasing stand age, whereas species diversity increased with increasing stand age. The relative proportions of trophic groups changed after crown closure from mostly granivores and omnivores to mostly insectivores. However, after mechanical thinning of late-age stands, small mammals of forested habitats and of early successional habitats were found together. The numbers of trapped small mammals decreased progressively throughout the study. We speculate that weather events might have contributed to this pattern but the reasons are unknown. INTRODUCTION Small mammals of forests often show preferences for habitats differing in age and structure (Linzey and Linzey 1973, Kirkland and Griffin 1974, Dueser and Shugart 1978). Thus, the abundance and species of small mammals inhabiting recent clearcuts often differ greatly from those found in maturing forests. Furthermore, secondary succession sometimes is governed by attributes of the initial disturbance (Boring et al. 1981 ). For example, timber management practices such as site preparation and the use of herbicides, pesticides, fertilizers, and selective cutting can directly affect the composition of the plant community, and in tum indirectly affect small mammal communities. Much research has evaluated changes in small mammal communities in relation Present address: USATC, 1407 Washington Blvd, Fort Eustis, Virginia 23604, James.d.dolan@us.army.mil. Corresponding author: Dr. Robert K. Rose, Department of Biological Sciences, Old Dominion University, Norfolk, Virginia 23529-0266, Email : brose@odu.edu Virginia Journal of Science, Vol. 58, No. 3, 2007 http://di it commons.odu.edu/vjs/vol58/iss3 148 VIRGINIA JOURNAL OF SCIENCE to vegetation changes in hardwood forest systems in eastern North America (e.g. , Kirkland 1977, McComb and Rumsey 1982, Martell 1983, Buckner and Shure 1985). However, fewer studies have been conducted on small mammals in pine plantations in the Southeast. Atkeson and Johnson (1979) and Mengak et al. (1989) studied small mammals in pine plantations in the piedmont regions of Georgia and South Carolina, respectively, and Mitchell et al. (1995) studied small mammals in pine plantations on cleared pocosins in coastal North Carolina. In contrast, our study examined small mammal communities in managed loblolly pine plantations on upland sites in the coastal plain of Virginia, a region in which commercial stands of such pines often locally comprise a majority of the forested landscapes. To learn details of changes in the small mammal community in relation to age of pine stand, we chose pine plantations of ages 1, 8, 18, and 24 years. In eastern Virginia, most loblolly pine (Pinus taeda L.) plantations are harvested at ca. 30 years of age. Our objectives were to determine the relative abundance, biomass, and species diversity of small mammal communities in relation to the age of managed pine plantations, to examine seasonal changes in the small mammal communities of these stands, and to document the presence or disappearance of small mammal species with age of pine stand. MATERIALS AND METHODS Study sites, selected from holdings of The Union Camp Corporation, were located in Isle of Wight County, in the Southeastern Coastal Plain Region of Virginia. Pine trees had been planted at densities of 1042-1482 stems/ha using mechanical planters after stumps and debris had been pushed into windrows. We chose four age classes of pine plantations on sites in relatively close proximity (1-16 km apart) to minimize the effects of variation in local weather conditions. We had no control over the herbicide, pesticide, or thinning treatments applied to some forest stands; we sought replicate sites that were as similar as possible. We had three replicates of the 1and 24-year-old stands, and two replicates of the 8and 18-year-old stands. We trapped during five seasonal periods: (1) 12 June 26 July 1995, (2) 20 October3 December 1995, (3) 19 January3 March 1996, (4) 3 April17 May 1996, (5) 9 July 22 August ,1996. The interval between seasons was at least 30 days. Small Mammal Trapping Effective surveys of small mammals require two methods of trapping, one of them being removal trapping (e.g., Getz 1961; Wiener and Smith 1972). Because pine forests support low-density populations of most small mammal species (Mengak et al. 1989, Mitchell et al. 199 5) and removal trapping can locally reduce population density, we chose to use four 0.25 ha grids separated from one another by at least 50 m rather than one large hectare grid at each site. This design produces twice as much edge as one large grid, enabling small mammals living on the margins to enter the 0.25 ha grids after pitfall trapping had reduced abundances within the grids, potentially allowing populations to recover quickly. The 50 m X 50 m (0.25 ha) grids were established at each site, each with 25 trap stations 12.5 m apart. A minimum buffer zone of 50 m separated grids from both the edge of a site and from one another. One Fitch live trap (Rose 1994) and one# 10 can '