Terrestrial Activity, Abundance and Species Richness of Amphibians in Managed Forests in South Carolina.

HUGH G. HANLIN [1]

ABSTRACT.--We determined the relative abundance, days of surface activity and indices of species diversity, evenness and richness for amphibians inhabiting three differently managed forests surrounding a Carolina bay in South Carolina following restoration. We collected animals daily for 3 y (Oct. 1993-Sept. 1996) using drift fences with pitfall traps in three forest types: loblolly pine (Pinus taeda), slash pine (P elliotti) and mixed hardwoods (predominantly oak, Quercus spp. and hickory, Carya spp.). Captured animals were marked and recaptures were recorded but not included in statistical analyses, except in our evaluation of activity. We compared results to those of a more limited study conducted before restoration.

Amphibians were significantly more numerous and more active in the mixed hardwood forest than in the pine forest types. However, the hardwood forest had the lowest species diversity in 2 of the 3 y of the study. The slash pine habitat had the highest diversity in all 3 y and for the 3 y combined. Because the evenness index (J') values differ in step with the species diversity index (H') it appears that the evenness component of diversity, rather than the richness component, is what is determining H' variation. A summer subset of these data and summer data from an earlier study of 1977-1978 is in marked contrast with yearlong patterns. For our summer data each forest type had the highest H' value in one of the years of the study and again the J' values parallel the differences in H'.

Large numbers of southern toads (Bufo terrestris) reduced evenness, and therefore species diversity, for all three habitats particularly the mixed hardwoods where this species was especially abundant. Proportionally lower numbers of B. terrestris in the summer samples increased J' and H' indices. Overall lower abundance and H' values in the summers of 1994-1996 compared with 1977-1978 may be the result of habitat alteration during the restoration of the Carolina bay.

INTRODUCTION

In recent years forest management practices of the forest products industry have received close scrutiny. The industry faces the challenge of developing management plans that optimize. the production of timber while maintaining environmental quality, including the functional integrity of wildlife habitats (Sharitz et al., 1992; Siegel, 1995).

For over 40 y, thousands of acres of the Savannah River Site near Aiken, South Carolina, have been managed by the United States Forest Service for production of pulpwood by harvesting planted pine plantations. Many of these managed forests are contiguous with Carolina bays, natural wetlands unique to the southeastern Atlantic Coastal Plain (Schalles et al., 1989). In addition to providing forage and water for upland wildlife, Carolina bays are particularly important sites for amphibian reproduction and larval development (Patterson, 1978; Sharitz and Gibbons, 1982; Pechmann et al., 1989). At least 34 species of amphibians have been reported from Carolina bays on the Savannah River Site (Schalles et al., 1989; Gibbons and Semlitsch, 1991); 31 of these are terrestrial for a portion of their life cycle. Therefore, alteration of terrestrial habitats, particularly those contiguous with these natural wetlands, may affect the life histories of the amphibian species. Amphibians have often been neglected when evaluat ing the impacts of forest management practices on wildlife (Bury et al., 1980; Bury, 1988; Wigley and Roberts, 1994), in spite of their vital position in forest food webs (Burton and Likens, 1975; Vitt et al., 1990), their value as indicators of habitat quality (Bury and Corn, 1988; Gibbons, 1988; Wake, 1991; Dunson et al., 1992) and endangered biodiversity (Dobson et al., 1997) and their apparent declining global populations (Blaustein and Wake, 1990). However, interest in the relationships of amphibian ecology and management practices is increasing (deMaynardier and Hunter, 1995).

Lost Lake, a Carolina bay located on the Savannah River Site, was ditched and drained for agricultural production from before 1943 until the early 1950s. After the Atomic Energy Commission removed the land from farming the cultivated area around the bay was planted in single-species stands of loblolly pine (Pinus taeda) in 1952 and slash pine (P. elliotti) in 1953. An uncultivated area remained in mature mixed deciduous hardwood species, primarily oak (Quercus spp.) and hickory (Carya spp.). The bay was allowed to refill and function as a wetland, although overflow from a settling basin for a nearby industrial complex contaminated the bay with a variety of pollutants, primarily cleaning fluids, solvents and heavy metals.

Based on aerial photographs from the late 1930s, the hardwood forest is more than 60 y old. The two pine forests surrounding Lost Lake have routinely been burned since their planting 45 y ago, the two most recent treatments occurring in 1980 and 1986. Prescribed burning reduces leaf litter, woody debris and shrubs in the understory. The relationship of forest habitat to the abundance and distribution of amphibians has been shown to vary with the amount of coarse woody debris (Welsh and Lind, 1991; Petranka et al., 1994), leaf litter depth and type (Pough et al., 1987; Corn and Bury, 1991), humus/soil acidity (Wyman and Jancola, 1992) and hardwood shrub abundance (Pough et al., 1987; Raphael, 1988). These habitat features are directly influenced by stand age, tree species composition and management practices (DeGraaf and Rudis, 1990; Grant et al., 1994; Dupuis et al., 1995).

In 1977-1978 Bennett et al. (1980) conducted one of the earliest examinations of the relationship of forestry practice and amphibian community structure at Lost Lake. Their study was designed to determine terrestrial activity, relative abundance and diversity of amphibians in the three forest types contiguous to the wetland which, because of pollution, no longer supported either emergent or submerged aquatic macrophytes. The forests were sampled from 3O June-10 Aug. 1977 and from 2O June-15 Aug. 1978. Bennett et al. reported that the three forests were similar in species diversity reported as H' for combined summer data and for the summer of 1978. The hardwood forest was reported to have a higher diversity in 1977. The hardwood forest also yielded approximately 50% more individual amphibians than either pine forest during both years.

In 1990 a closure plan for the settling basin near Lost Lake was developed which included, in addition to closing the basin, the restoration of the degraded Carolina bay to a "natural wetland system" (Gladden et at., 1992). The surrounding forest within a minimum radius of 50 m was removed and the bay was drained. All vegetation from the removal action was burned and the residual ash and contaminated sediments were moved to the settling basin and compacted. After replacement of removed sediments with "clean" soil the bay was allowed to refill and aquatic vegetation was planted. Before restoration Lost Lake had a surface area of approximately 2 ha (Schalles et at., 1989). Based on a 1996 aerial photograph the current surface area is approximately 6.5 ha.

Since 1993 we have studied the amphibians and their colonization of Lost Lake in an effort to assess the success of restoration. Because the amphibian populations colonizing the wetland inhabit or migrate through the three adjacent forests, we were also able to reevaluate the relative abundance, diversity and fluctuations of the populations in each of the three forests and to compare our results with prerestoration data (Bennett et al., 1980).

METHODS

Study site.--The dominant aquatic plants in Lost Lake are cattail (Typha latifolia and floating heart (Nymphoides cordata) which are unevenly distributed in the littoral zone. Based on the wetland vegetation indicator categories presented by Reed …