Evaluating tree colonization on reclaimed mines in the northern anthracite fields of Pennsylvania

Background/Question/Methods . Since the late 1970s, sites impacted by coal mining have been reclaimed by re-grading and subsequently planting them with mixtures of cool-season grasses and legumes. While the meadows resulting from that approach have higher ecological value than unreclaimed sites, they represent artificial plant communities, especially in the eastern United States. Such meadows appear to resist invasion by native woody species, thus inhibiting succession to forest. Long-term investigations of such sites are rare, however. A 220-acre anthracite mine in northeastern Pennsylvania reclaimed using grasses and legumes in 1997 showed little evidence of tree colonization by 2003. Follow-up visits in 2008 showed portions of the site to be wooded by black locust (Robinia pseudoacacia), which is considered invasive in that part of the state. An analysis was conducted to investigate whether black locust could facilitate the colonization of later successional hardwood trees, especially from remnant forest bordering to the south. Stem density of woody plants, herbaceous plant cover, and presence of tree seedlings were determined in plots systematically arrayed throughout the site beginning in July 2009.

Results/Conclusions . All plots contained high densities (85%) of cool-season grasses, legumes, and other broadleaf herbs. Black locust trees growing to 15-20' tall were found in 75% of the plots. Plots also included non-native trees introduced during community planting projects in the past five years. No native tree species typical of regional mature forests were noted in any of the plots, however, even as juveniles under black locust canopy. Nor was any evidence of colonization by natives seen at the edge of the mine adjoining the intact forest. These results suggest that even though the site is shifting from meadow to forest, it does not appear to be on a trajectory leading to a species composition typical of regional forests. Thus, introduction of such species may be needed, following a Forest Reclamation Approach (FRA).