Unconventional natural gas development has been rapidly proceeding for the past decade in many parts of the United States, particularly Pennsylvania. Transporting gas to market requires the build-out or enlargement of a projected 30,000 miles of natural gas pipelines over the next 20 years, fragmenting forests throughout the state. Many people are concerned that pipeline rights-of-way (ROW) represent likely avenues for the spread of alien and invasive plant species into areas currently dominated by native forests. To understand the process of revegetation on pipeline ROW, we initiated a multi-year assessment within a 1700’ long segment of Transco Pipeline in eastern Pennsylvania that underwent expansion in 2016. Plants were identified and percent covers assessed within forty-eight 3x1m plots in upland and wetland parts of the site. Controls included portions of the ROW that were not impacted during expansion (32 plots). Total percent cover, number of species per plot, and Shannon-Weiner diversity indices were calculated.
Results/Conclusions
Within the plots sampled from the recently disturbed ROW in early summer 2017, average percent cover ranged from 30% to 54%, depending on position within the site. In contrast, cover was 83-107% in the plots sampled in undisturbed ROW, indicating that the rate of revegetation on the recently disturbed plots was proceeding more slowly than expected. Shannon-Weiner diversity was also lower in the disturbed (H’ = 1.16 – 2.20) than in the undisturbed (H’ = 2.64 – 2.77) section of the ROW. Roughly half of the cover in the recently disturbed plots was Lolium multiflorum that was seeded as a nurse crop. The other half was a mixture of non-native wildflowers and grasses, most of which were also seeded. Plant density and diversity were higher in the wetland part of the disturbed ROW than in the upland, indicating that lack of soil water might have limited revegetation. By late summer, the L. multiflorum had largely senesced, and % cover in the recently disturbed section of the ROW was mostly <40%, indicating that the revegetation effort was less than hoped. The site will continue to be monitored into the growing season of 2018 and beyond.