396 (Bramble et al. 1997; Litvaitis et al. 1999; Yahner et al. 2004, 2007; Komonen et al. 2013; Wagner et al. 2014; Berg et al. 2016; Wagner et al. 2019). In the northeastern United States and elsewhere, where early successional landscapes are disappearing (Litvaitis et al. 1999; DeGraaf and Yamasaki 2003), electrical transmission ROW may support numerous species of conservation concern that rely on this habitat type (e.g., DeGraaf and Yamasaki 2003; Ballard et al. 2007; Wagner et al. 2014). Furthermore, flowering plants are critical for pollinator populations and the species richness of this native plant community type, which provides the basis of food webs for native bees— wildlife in dramatic decline (Wagner et al. 2019). Despite these wildlife studies in powerline rights-of- way, Wagner et al. (2014) and Richardson et al. (2017) indicate that vegetation studies have primarily focused on rare or endangered plants (e.g., Tompkins 2013) and the maintenance of early successional vegetation that is resistant to tree invasion (Bramble et al. 1991; Bramble et al. 1996; De Blois et al. 2004; Yahner and Hutnik 2005). Surprisingly, the number of studies that focus on native flowering plant communities (in terms of native species richness) under transmission lines is small (see Wagner et al. 2014). However, recent work has begun to focus on the effects of specific her- bicide mixtures and IVM on non-target plants and overall species richness under transmission lines (Clarke et al. 2006; Wagner et al. 2014; Isbister 2016; Wagner et al. 2019). This research is a continuation of a project that began in 1953 when researchers at The Pennsylvania State University designed an initial electric transmis- sion ROW study to test the effects of selective herbi- cide use and other vegetation management approaches on native plant and wildlife communities (e.g., Bramble and Byrnes 1979) in an electric transmission ROW. The project was initiated on State Game Lands (SGL) 33 in Centre County, Pennsylvania, with several part- ners, including Pennsylvania Electric Company (now First Energy Corp.), the Pennsylvania Game Commis- sion, DuPont, AmChem (now Corteva), and Asplundh Tree Expert Co. The year 2018 marked the 65th year of the original study—making SGL 33 the site of the longest continuous study measuring the effects of herbi- cides and mechanical vegetation management practices on vegetation structure, wildlife habitat, and wildlife use within a ROW. Due to the continuous nature of the project, pre-treatment condition (pre-1953) was ©2020 International Society of Arboriculture Mahan et al: Native Plants on Rights-of-Way mixed-deciduous forest, and current plant and wildlife communities persist in response to decades of vegeta- tion management. The objective of this study was to determine how herbicide or mechanical vegetation management approaches affect the number of trees and native compatible flowering plant species present on the ROW. This study focuses solely on native plant species that occur on the ROW. MATERIALS AND METHODS During July to August 2012, 14 sections (20 m × 200 m) of the ROW at SGL 33 located directly under a 230-kV electric transmission line (area defined as the wire zone) were managed with either IVM, chemical (herbicide), or mechanical treatments (mowing or hand cutting) to remove or limit tree growth (Table 1). Four of these sections were managed with nonselective mechanical treatments (e.g., all vegetation was cut to a height of 1 m with mowers or chain saws), and ten were treated with herbicide applications that were either applied broadly or selectively depending on site conditions and IVM prescriptions (see Table 1 for specific commercial/ chemical herbicides used). In 2016, we sampled native flowering plant vegetation in late July to corre- spond to maximum plant emergence at our study sites, realizing the plants with short growing and/or bloom- ing seasons (e.g., spring ephemerals, fall asters) may be missed. We used sampling techniques developed for the research project (see Bramble et al. 1991) that were modified from vegetation sampling techniques developed by Braun and Blanquet (Moore 1962; Wagner et al. 2014). All trees at least 0.3 m in height were recorded within 3 permanent transects (each 20 m long × 2 m wide) in wire zones of each section. Only trees rooted in a transect were counted (i.e., trees rooted outside the transect with foliage extending into the transect were not counted). We then calculated the total number of trees in each treatment section and presented trees as a per hectare (ha) figure. Additionally, we determined the species richness of native flower- ing plants under 2 m in height that were compatible with ROW maintenance (e.g., forbs or plants with shrubby-growth form). These plant species were counted within a 5-m radius plot placed in the center of each transect. We also determined the dominant (> 50% of area) cover type along each transect. For species rich- ness, native grasses (sedges Carex sp.) were included as one species. All other grasses were non-native and listed only as cover type. We calculated a Pearson
November 2020
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