Species-specific facilitation shapes primary successional communities under nurse trees in an abandoned slag dump

Facilitation by nurse plants shapes community development during primary succession. Human activity—especially in urban settings—has created environments like abandoned lots or post-industrial waste sites in which primary succession occurs. The importance of facilitation in these stressful urban habitats is likely pronounced. There is evidence that facilitative interactions are species-specific and reflect the interactions of different combinations of plant species. We test the hypothesis that colonizing species abundance will differ between focal host tree species due to differing effects on microhabitat character. Alternatively, colonizing species’ distributions may instead reflect environmental heterogeneity independent of host species. We sampled vegetation under 13 trees on a slagheap in Pittsburgh, PA, USA. Focal trees included Ailanthus altissima (n = 4), Rhamnus cathartica (n = 4), and Ulmus parvifolia (n = 5). Vegetation was surveyed and environmental variables were measured at the base of each tree. Species richness was compared between tree species at a larger cluster and smaller 1m 2 plot scales to assess scale-dependent patterns. Eight woody species were tested for differences in abundance between focal tree species. Shrubs and vines responded to different variables individually, including environmental factors and focal tree species. Non-native richness differed significantly with soil temperature but not between tree species. Though all focal trees in this study are non-native, we conclude that they facilitate establishment of both native and non-native species. Retention of nurse trees in post-industrial environments, even non-native individuals, may therefore contribute to revegetation of native species.