Abstract
The Green Lane Research and Demonstration Area, Montgomery County, Pennsylvania, U.S., has been studied each year since 1987, making this 21-year-old project extremely valuable as a source of information on the effects of mechanical and herbicidal maintenance on flora and fauna along an electric transmission right-of-way (ROW). In this article, our objective was to document plant species richness among treatment units and in relation to wire and border zones on the ROW. We noted the presence of plant species from late May through mid-August in 2005 and 2006 and observed 114 vascular plant species in the ten treatment units; 35 (31%) of these species were exotic. Twenty-seven (24%) species were widespread on the ROW and seven of these (26%) were exotic. The total number of species per unit ranged from 46 (40%) species in handcut units to 57 (50%) in stem–foliage spray units. Of the total number of species, 103 (90%) and 81 (71%) occurred in wire and border zones, respectively. The number of exotic species was higher in wire zones (33 [29%]) than in border zones (22 [19%]).
- Exotic species
- herbicides
- integrated vegetation management
- rights-of-way
- southeastern Pennsylvania
- species richness
- tree control
- vegetation
A major goal of the Green Lane 33 Research and Demonstration Project in southeastern Pennsylvania, U.S. since its establishment in 1987 has been to determine the use of Integrated Vegetation Management (IVM) for maintenance of an electric utility transmission right-of-way (ROW) (Bramble and Byrnes 1996; Yahner and Hutnik 2004a). The response of vegetation to IVM is important because plant communities can change within a relatively short time because of natural plant succession.
The IVM technique for vegetation involves two phases: 1) use of a herbicidal spray or mechanical treatment to initially control the density of target (undesirable) trees, i.e., those that have the potential of growing to a height that is not compatible with safe ROW maintenance; and 2) development of a tree-resistant plant cover type to reduce target tree invasion of the ROW (Bramble and Byrnes 1996; Yahner and Hutnik 2004a). The wire–border zone method was used on all treatment units of the Green Lane Research and Demonstration ROW to achieve this goal (Yahner and Hutnik 2004a, 2005; Ballard et al. 2007).
The Green Lane Research and Demonstration Area has been studied each year since 1987, making this 21-year-old project extremely valuable as a source of information on the effects of mechanical and herbicidal maintenance on flora and fauna along an electric transmission ROW (Yahner and Hutnik 2004a, 2004b). A desired objective of IVM on the Green Lane Research and Demonstration Area is to create a diversity of plant species, which in turn provides a diverse wildlife habitat (Yahner and Hutnik 2004a). On a broad scale, habitat diversity on the ROW is achieved by herbicidal and mechanical maintenance of treatment units through the wire–border zone method. However, on a smaller scale, plant species diversity also is achieved by the presence of different combinations of shrub, forb, and grass cover types.
In this article, our objective was to document plant species richness among treatment units and in relation to wire and border zones on the Green Lane Research and Demonstration ROW. Species richness is a simple, yet important, measurement of species diversity and is the total number of different species in a given area (Yahner 2000).
STUDY AREA AND METHODS
The study area consists of 10 units with two replicates of each of five treatments (mowing, mowing plus herbicide, stem–foliage spray, foliage spray, and handcutting) (Table 1) (see Yahner 2006 for details of treatments). The total area of the ROW is 5.43 ha. Each treatment unit is rectangular in shape, ranges from 0.38 to 2.47 ac (0.15 to 1.00 ha), and spans the width of the ROW. The western border zone (7 m wide) of the ROW is immediately adjacent to a ROW of Pennsylvania Power & Light Company (PP&L); thus, vegetation was measured only along eastern border zones (11.5 m [37.95 ft] wide). As part of the vegetation assessment of treatment units of plant species from late May through mid-August in both 2005 and 2006, presence of each plant species was noted relative to wire versus border zone in each treatment unit. We used correlation analyses to determine if either the total number of species or the number of exotic species was correlated with size of units (Sokal and Rohlf 1995).
Total number of plant species in wire zones, in border zones, and in either zone of ten treatment units at the Green Lane Research and Demonstration Area from late May through mid-August 2005 to 2006.z
RESULTS AND DISCUSSION
We observed 114 vascular plant species in 10 treatment units on the Green Lane Research and Demonstration ROW during 2005 to 2006 (Table 1; Appendix). This total number of species at Green Lane was less than the 125 species noted along a transmission ROW in central Pennsylvania (State Game Lands [SGL] 33), but the SGL 33 ROW consisted of 15 units (Yahner and Hutnik 2005).
Total number of species per unit at the Green Lane Research and Demonstration ROW ranged from 46 (40%) in handcut units to 57 (50%) in stem–foliage units (Table 1; Appendix). Only 27 (24%) of the total number of species were considered wide-spread (e.g., those found in 80% or more of the units), and seven of these (26%) were exotic. In comparison, 35 (31%) of the total number of species were exotic. This percentage of exotic species is considerably higher than that noted on the SGL 33 ROW (23%), which traverses a relatively pristine forested landscape (Yahner and Hutnik 2005), or that found in unfragmented forest stands in Wisconsin (20%) (Rooney et al. 2004). The Green Lane ROW traverses residential areas that have been human-impacted for decades; thus, the number of exotic species was expected to be high on the Green Lane ROW, like in a sector of Valley Forge National Historical Park (34%) in southeastern Pennsylvania (Cypher et al. 1986; see also Lundgren et al. 2004).
Of the total number of species, 103 (90%) and 81 (71%) were in wire and border zones, respectively (Appendix). In wire zones, number of species ranged from 34 (30%) in mowing plus herbicide units to 50 (44%) in stem–foliage units (Table 1). In border zones, number of species varied from 26 (23%) in hand-cut units to 36 (32%) in foliage–stem units. The number of exotic species ranged from 33 (29%) in wire zones to 22 (19%) in border zones (Appendix). The total number of species or number of exotic species were not correlated with size of units (r = 0.19 and 0.08, respectively; P > 0.90). Also, because exotic species were found throughout the ROW, the proximity to a road was not a factor in determining the current distribution of exotic species (Brothers and Spingarn 1992; Watkins et al. 2003; Yahner and Hutnik 2005).
Acknowledgments
Cooperators were Asplundh Expert Tree Company, Dow AgroSciences, and Philadelphia Electric Company.
APPENDIX
Plant species (in phylogenetic order) noted in wire zones (W), in border zones (B), in both zones (WB), or absent (−) in ten treatment units on the Green Lane Research and Demonstration Area from late May through mid-August 2005 to 2006.z
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