Abstract
A 2-year study of reptile and amphibian populations was conducted on a 230-kV transmission line right-of-way (ROW) of GPU Energy in the Allegheny Mountain Physiographic Province, Centre County, Pennsylvania, U.S., from June through October 1998 and March through October 1999. The objective was to compare the diversity and relative abundance of reptiles and amphibians between the ROW versus the adjacent forest, among five treatment units on the ROW, and between wire and borders zones on treatments on the ROW. Nine species were recorded during the study, with the three most common species being redback salamanders (Plethodon cinereus), northern redbelly snakes (Storeria occipitomaculata occipitomaculata), and northern ringneck snakes (Diadophis punctatus edwardsii). All nine species occurred on the ROW, but only redback salamanders and Jefferson salamanders (Ambystoma jeffersonianum) were found in the adjacent forest. The diversity and relative abundance ranged from six species in the stem-foliage unit to three species in the handcutting unit. Eight and six species, respectively, were noted in the wire and border zones of the ROW. However, 81% of the observations in wire zones were those of snakes, whereas 85% of the observations in border zones were salamanders. The ROW contained a much more diverse community of reptiles and amphibians than the adjacent forest. Forest-management practices can have negative impacts on populations of amphibians and reptiles. Thus, this study provides important information on forest-management practices required for the conservation of reptiles and amphibians.
Forest-management practices can have negative impacts on populations of amphibians and reptiles (e.g., Ash 1997; deMaynadier and Hunter 1998; Rodewald and Yahner 1999). From an ecological perspective, woodland salamanders comprise a major portion of the total vertebrate biomass in an ecosystem (Burton and Likens 1975). Amphibians (e.g., woodland salamanders) feed on a variety of invertebrates, whereas reptiles (e.g., snakes) feed on both invertebrate and small mammals (Shaffer 1991). These vertebrates are important components of the food chain. There is increasing global concern for the decline of amphibian populations (Blaustein and Wake 1990; Fisher and Shaffer 1996).
Vegetation management along a 4.8-km (10-mi) portion of the right-of-way (ROW) in Centre County, Pennsylvania, U.S., has been studied since 1953 (Yahner et al. 1999a). The ROW is a 230-kV transmission line of GPU Energy in the Allegheny Mountain Physiographic Province. The project addresses two long-term objectives since its inception: 1) to compare the effectiveness of commonly used herbicide and mechanical maintenance treatments on control of target trees and development of tree-resistant plant cover types to handcutting without herbicides, and 2) to determine the effect of these maintenance treatments on selected wildlife species of high public interest.
The objective was to compare the diversity and relative abundance of reptiles and amphibians between the ROW versus the adjacent forest, among five treatment units on the ROW, and between wire and borders zones on treatments on the ROW Because forest-management practices can have negative impacts on populations of amphibians and reptiles, the study is timely from an ecological and publicrelations perspective.
METHODS
Five treatment units were selected for study: 1) handcutting, 2) high-volume basal spray, 3) mowing plus herbicide, 4) stem-foliage spray, and 5) foliage spray. Beginning in 1982, each unit was treated using the wire zone-border zone method (Figure 1). This method is designed to produce a tree-resistant low shrub-forb-grass cover type on the wire zone and a tall shrub-forb cover type on the border zone. Each of the units was treated by herbicides and/or mechanical in 1987 and again in 1996. Details of these treatments can be obtained in Bramble et al. (1999) and Yahner et al. (1999a).
Diagram of a 230-kV line and ROW showing wire and border zones. A low shrub-forb-grass cover type is found in the wire zone, and a tall shrub-forb cover type is present in the border zone.
The handcutting unit had a tree-shrub cover type on both wire and border zones; oaks (bear oak [Quercus ilicifolia] and various oak species [Quercus spp.]) predominated in the wire zone, and oaks, blueberry (Vaccinium spp.), and blackberry (Rubus alleghenensis) were common in the border zone of this unit. The high-volume basal spray unit was characterized by a shrub-forb cover type on both wire and border zones, including mountain laurel (Kalmia latifolia), sweet fern (Myrica peregrina), blueberry, blackberry, witchhazel (Hamamelis virginiana), and goldenrod (Sołidago spp.). The mowing plus herbicide consisted of a grass-forb cover type on the wire zone and a shrub-forb cover type on border zones. In the wire zone, grasses (e.g., fescue [Festuca elatior] and poverty grass [Danthonia spicata]) and hay-scented fern (Dennstaedtia punctilobula) were common. In the border zone, witchhazel, blueberry, sweet fern, hay-scented fern, and goldenrod were abundant. The stem-foliage spray had a forb-shrub cover type on the wire zone, consisting mainly of hay-scented fern and goldenrod, and a shrub-forb-grass cover on the border zone, comprised of witchhazel, sweet fern, blueberry, hay-scented fern, and poverty grass. The foliage spray was characterized by a shrub-forb-grass cover type on both zones, and principal species were blueberry, blackberry, sweet fern, hay-scented fern, and poverty grass.
Three sampling points were established in the wire zone, in the border zone, and 40 m (131 ft) into the adjacent forest in each treatment unit, giving nine sampling points per unit. A distance of 40 m from a forest edge was used for sampling points into the adjacent forest because woodland salamanders may be relatively scarce within 25 m (82 ft) of edges (deMaynadier and Hunter 1998). At each sampling point, one large coverboard (waferboard, approximately 30 × 120 × 1.5 cm [12 × 48 × 0.6 in.]) and three small coverboards (untreated pine, approximately 15 × 90 × 2 cm [6 × 36 × 0.8 in.]) were placed flush with the soil surface (DeGraaf and Yamasaki 1992; Rodewald and Yahner 1999; Yahner et al. 1999b) (Figure 2).
A large coverboard (background) and a small coverboard (foreground) are seen at a sampling point in the forest adjacent to the right-of-way (photo taken by RHY in July 1999).
Coverboards were checked at each sampling point one to three times per season (spring, summer, and autumn) for the presence of reptiles and amphibians beneath them (Rodewald and Yahner 1999; Yahner et al. 1999b). These coverboards represented potential refugia and resting sites for reptiles and amphibians. During each sampling period, at least 1 hour was spent searching for reptiles and amphibians on the soil surface in wire zones, border zones, and adjacent forest. In 1998, rocks and logs were overturned to check for reptiles and amphibians for comparison to data collected beneath coverboards (Yahner et al. 1999b).
RESULTS AND DISCUSSION
Diversity and Relative Abundance on ROW Versus Adjacent Forest
Nine species of reptiles and amphibians were observed on the right-of-way and in the adjacent forest in 1998 and 1999 (Table 1). All nine species were found on the ROW, whereas only two species occurred in the adjacent forest. These included 137 observations of one toad species, three salamander species, and five snake species. Because animals observed were not permanently marked for individual recognition, the same individual may have been observed more than once during the study However, sampling periods were spaced at least 2 to 3 weeks to minimize recounting the same individual more than once.
Diversity and relative abundance of reptiles and amphibians under coverboards, rocks, or logs or on the soil surface on the ROW and in adjacent forest in Centre County, Pennsylvania, 1998-1999.
The three most common species in decreasing order of relative abundance were redback salamanders (n = 71 observations or 52% of total), northern redbelly snakes (n = 27, 20%), and northern ringneck snakes (n = 15, 11%) (Table 1). In several studies of terrestrial salamander populations in the northeastern United States, redback salamanders are the most abundant species of salamander (e.g., DeGraaf and Yamasaki 1992; Rodewald and Yahner 1999). Although timber rattlesnakes (Crotalus horridus) were once common on the ROW when it was first established in the 1950s (W C. Bramble, personal observation), none was found in our study Timber rattlesnakes, like many terrestrial salamanders, are species of special concern and are in need of protection (Yahner 2000).
More observations of salamanders were in the forest (n = 45, 59%) than on the ROW (n = 35, 41%) (Table 1). Based on the number of coverboards in the forest versus the ROW only two-thirds of the salamanders would be expected to occur in the forest. Thus, although salamanders occurred on the ROW, they showed a preference for habitat in the adjacent forest. Salamanders require the moister microclimatic conditions for foraging and breeding (Shaffer 1991), which were present in the adjacent forest compared to the dryer conditions on the ROW In contrast, snakes were found exclusively on the ROW which provided a combination of shrubby and grassy habitat for these species.
Diversity and Relative Abundance per Treatment Unit
Ninety-two reptiles and amphibians were recorded on the five treatment units in 1998 and 1999 combined (Table 2). The most common species was the redback salamander (34% of total), followed by the northern redbelly snake (29%) (Figure 3) and the northern ringneck snake (16%).
Diversity and relative abundance of reptiles and amphibians in five treatment units on the ROW in Centre County, Pennsylvania, 1998-1999.
A northern redbelly snake under a coverboard in a stem-foliage spray treatment unit in May 1999. This species, which feeds on insects and other invertebrates, was the most common snake found on the ROW Adult redbelly snakes are only about 20 to 25 cm (8 to 10 in.) in length. They are very secretive and are seldom found, even by those who spend a considerable time in the outdoors. Thus, the use of coverboards is an effective way to monitor this species on a ROW (photo taken by RHY).
The number of species per treatment unit varied from six species in stem-foliage spray to three in handcutting (Table 2). Twenty-four reptiles and amphibians were found in each of the high-volume basal spray, stem-foliage spray, and foliage spray units. The shrub-forb-grass cover types in these three units provided a diverse habitat for a variety of reptiles and amphibians. In contrast, only four reptiles and amphibians were noted in handcutting. The cover type in this unit was relatively homogeneous and was similar to young, even-aged forest stands, which are of little value to amphibian and reptiles as habitat (Rodewald and Yahner 1999).
Diversity and Relative Abundance in Wire Versus Border Zones
Eight and six species of reptiles and amphibians, respectively, were found in wire and border zones on the ROW in 1998 and 1999 (Table 3). In addition, 63% of the sightings occurred in wire zones compared to 34% border zones. Eighty-one percent of the sightings in wire zones, however, were those of snakes, whereas 85% in border zones were those of salamanders. A ROW using the wire zone-border zone method (Figure 1) creates suitable habitat for both terrestrial salamanders and snakes (Figure 3).
Diversity and relative abundance of reptiles and amphibians in wire versus border zones on ROW in Centre County, Pennsylvania, 1998-1999.
CONCLUSIONS
The ROW in this study contained a much more diverse community of reptiles and amphibians than the adjacent forest. With the exception of handcutting, all treatment units provided suitable habitat for these vertebrates. The border zones of the ROW ensured moist microenvironments for salamanders, and the wire zones provided suitable habitat for snakes. Utility companies are encouraged to adopt the wire zone-border zone method because it provides acceptable habitat for a variety of reptile and amphibian populations noted in this study.
Acknowledgments
Cooperators were Asplundh Tree Expert Company, Dow AgroSciences, GPU Energy, and the Pennsylvania Game Commission. We thank K.L. Derge for a critical review of the manuscript.
- © 2001, International Society of Arboriculture. All rights reserved.
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