148 Yahner et al.: Long-Term Trends in Small Mammals Figure 1. Diagram of a 230 kV electric transmission line showing wire and border zone. A combination of a low- growing forb-shrub-grass cover type usually develops in the wire zone, and a tall shrub cover type occurs in the border zone. Adjacent to the border zone is mature forest. Forest cover type was located 50 m (165 ft) adjacent to the ROW (near a handcut and a basal low-volume spray unit); dominant trees were chestnut oak (Quercus montanus), north- ern red oak (Quercus rubra), white oak (Quercus alba), and black oak (Quercus velutina). Tree sprout cover type was produced by a handcut unit with common tree species being chestnut, northern red, white, black, and scrub (Quercus il- icifolia) oaks and black cherry (Prunus serotina). Tall shrub cover type predominated in border zones of several treatment units, e.g., mowing plus herbicide, with a dominant tall shrub of witchhazel (Hamamelis virginiana). Short shrub cover type commonly occurred in wire zones of some units, e.g., basal low-volume spray, and the principal plant species were blueberry (Vaccinium vacillans and Vaccinium angustifo- lium), huckleberry (Gaylussacia baccata), and sweet-fern (Comptonia peregrina). Cane thicket cover type was present in pure stands of some wire zones, e.g., basal low-volume spray, and the major species was common blackberry (Rubus allegheniensis). Forb-grass cover type was common in wire zones of mowed plus herbicide units; major species included goldenrod (Solidago rugosa and Euthamia graminifolia), hayscented fern (Dennstaedtia punctilobula), and poverty grass (Danthonia spicata). Grass cover type was present in wire zones of some units treated with mowing, which often contained dense stands of tall meadow fescue (Festuca elatior). Mammals were surveyed monthly from May through No- vember in 2004 and 2005 in each of the seven cover types. Six metal live traps were spaced in a 2 × 3 grid in a 10 × 15 m (33 × 50 ft) area in each cover type (after Yahner 1988). Traps were baited with a small amount of peanut butter, and a ball of fiber was placed in each trap for bedding just before dusk. Each trap was checked for captured small mammals on two consecutive mornings. Species, number of individuals trapped, date of capture, and location of capture relative to cover types were noted for each monthly survey (Smith and Vrieze 1979; Yahner 1983). Sex (if known), age (if known), reproductive condition (e.g., pregnant, lactating, scrotal), and individual identification (e.g., ear tag or toe clip) were re- corded for each captured mammal (Rose and Dueser 1980). A total of 588 trap-nights (TN) was sampled per year based on seven monthly surveys per year. RESULTS AND DISCUSSION Figure 2. A northerly view of the right-of-way on the State Game Lands 33 Research and Demonstration Area, Cen- tre County, Pennsylvania. In the foreground is a basal low-volume spray unit showing the foliage of black chokeberry (Aronia melanocarpa). The flagging is the location of a permanent plot used for vegetation transect establishment (photo by R. Yahner, early November 2005). ©2007 International Society of Arboriculture One hundred twenty-one individuals of eight small mammal species were found on the ROW and adjacent forest in 2004 and 2005 combined (Table 1). In contrast, seven species were noted on the ROW in 1989 and 1990 (Bramble et al. 1992). Based on 1176 total TN in the current study, capture fre- quency in all cover types and both years combined repre- sented 10.3 animals captured/100 TN; in 1989 and 1990, number of individuals captured/100 TN in all cover types combined on the ROW averaged 27.0 (Bramble et al. 1992). We have no biologic explanation for this reduction in small mammals from 1989 and 1990 to the current study that could be attributed to population cycles, differential predation rates, or herbicidal use. Significant differences in mammal popula- tions have been noted elsewhere in central Pennsylvania for no apparent reason (Yahner 1988). One factor may be in the impact of herbicidal use on small mammals, but no long-term impact has been noted on bird populations (or their food resources, e.g., insect larvae) on the same ROW (Bramble et al. 1999; Yahner et al. 2002). Six and eight species were noted on the ROW in 2004 and 2005, respectively (Table 1). Similarly, number of individual animals captures/100 TN was lower in 2004 (6.3) than in 2005 (14.3). In contrast, the small mammal community on
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