Plant Species Richness on an Electric Transmission Right-Of–Way Using Integrated Vegetation Management

RESULTS AND DISCUSSION

We observed 125 vascular plant species in the 15 treatment units on the SGL 33 Research and Demonstration Area during the 2 years (Table 1 and appendix). The total number of species per unit ranged from 35 species in a mowing unit (M-1) to 63 species in a basal low-volume unit (BLV-3) (Figure 2).

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Figure 2.

A basal low-volume spray unit (BLV-3). Note the diversity of plant species in this unit (photo credit: R. Yahner, July 2003).

Another unit with a high number of plant species was a handcut unit (HC-2), which also was quite heterogeneous in plant structure (Table 1 and appendix). Two reasons for this heterogeneity is that this unit was originally a mowing unit and is in the process of being converted to a handcut unit (Yahner and Hutnik 2004b). Hence, it has mowed areas on one portion and woody areas on another portion of the wire zone, which was quite rocky and difficult for a mower to treat the unit. Furthermore, the southern portion of this unit was once traversed by an unimproved dirt road, which likely facilitated dispersal of seeds into this area.

Of the total number of plant species found on the ROW, 95 (76%) and 110 (88%) occurred in wire and border zones, respectively (Table 1 and appendix). In wire zones, the average number of plant species ranged from 31 in mowing units to 41 in stem–foliage spray units. In border zones, the average number of plant species varied from a low of 34 in mowing units to a high of 41 in handcut units. Fourteen species were found only in wire zones, whereas 27 species were exclusive to border zones. Only five species occurred in all 15 units.

Of the total number of plant species, 23% were exotic species (Table 1 and appendix). This number is similar to 20% exotic plant species noted in unfragmented forest stands in Wisconsin (Rooney et al. 2004).

The proportion of exotic species did not vary appreciably between wire and border zones (19% and 22% of total, respectively) on the ROW (Table 1 and appendix). However, the three units adjacent to unpaved state forest roads with high rates of vehicular traffic (SF-2 and MH-3 adjacent to Hannah Furnace Road, BLV-3 bisected by Strawband Beaver Road) not only had the highest number of total species in the unit (55 to 63 species) but also the highest number of exotic species (13 to 16 species). Hence, vehicular traffic and roadside management (and perhaps disposal of unwanted landscape clippings and plants along the roadside) may be responsible in part for the invasion of seeds or other means of plant dispersal to these units. Other studies have found that exotic species were more common in forests and grassland near habitat edges, such as those at a road interface (Brothers and Spingarn 1992; Tyser and Worley 1992; Watkins et al. 2003; Pauchard and Alaback 2004). If forest roads in our study were paved, the number of exotic plant species could have been higher (Lundgren et al. 2004). Because units relatively isolated from state forest roads tended to have fewer exotic species, these sections of the ROW can serve as refugia for native flora (after Strittholt and DellaSalla 2001).