The resistance of diverse communities to biological invasion has led some ecologists to argue that conservation of local species diversity maintains both biodiversity and stability. Conservation of global biodiversity, however, will likely benefit more from high percent endemism of assemblages than from high local species richness. Therefore, diversity-invasibility studies need to address how the relative abundance of endemics and widespread generalists affect invasion. In a novel approach to community invasibility, we tested whether increased plant species richness or dominance by native endemic species was more important in competitively suppressing an established invader. We initiated a field competition experiment in an oak-hickory woodland in north-central Mississippi between the non-native invasive grass, Microstegium vimineum, and six native plant species with varying fidelity to open woodlands. Using a split-plot design, we applied the following planting treatments to established patches of Microstegium in the fall of 2014: (1) a six-species polyculture (2) a monoculture of six individuals of a single species, and (3) a control simulating the soil disturbance of planting. We then monitored transplant survival and quantified the emergence of Microstegium seedlings the following growing season.
Results/Conclusions
Survival of the native species was high, with 85% of all transplants emerging in the spring of 2015. Initial percent cover of emerging seedlings of Microstegium was significantly lower in polyculture and monoculture subplots than in control subplots, but did not differ between polycultures and monocultures, overall. However, emergence of Microstegium was significantly lower in polycultures than in monocultures of species with relatively high fidelity to open woodlands (i.e. endemics). Conversely, there was no difference in Microstegium emergence between polycultures and monocultures of widespread generalist species. Our preliminary results suggest that native plants can be successfully transplanted into established patches of a highly invasive grass, survive, and reduce its emergence. We will continue to monitor transplant survival and Microstegium cover and emergence through at least May 2016 to determine if these initial responses persist. If they do, then diverse plantings inclusive of endemics and potentially more competitive generalists may offer biotic resistance to an established invader while simultaneously restoring biodiversity characteristic of a globally rare habitat.