Evaluation of resource-limiting strategies intended to prevent Phalaris arundinacea (reed canarygrass) invasions in restored sedge meadows

Resource-rich restoration sites are prone to invasion by aggressive plants that prevent community recovery. Reducing light by sowing non-persistent cover crops and immobilizing nitrogen by amending soils with sawdust, however, may prevent this scenario in restored sedge meadows by limiting Phalaris arundinacea (reed canarygrass) invasions. To determine the usefulness of these resource-reducing methods, a perennial target community and Phalaris were sown with a high-diversity cover crop, a low-diversity cover crop, or no cover crop in plots with or without sawdust under controlled hydrological conditions. Aboveground biomass was measured after two growing seasons, and light and soil nitrogen were measured throughout the study. Only high-diversity cover crops reduced light, and in doing so they decreased target community and Phalaris establishment by 73% and 68%, respectively, resulting in a Phalaris-dominated community. Despite only reducing nitrogen over the short term, amending soils with sawdust decreased Phalaris establishment by 56% without hindering target community establishment, resulting in a graminoid-rich community similar to natural sedge meadows. The target community, however, reduced both light and nitrogen, and in doing so decreased Phalaris establishment by 78% and 67% in plots with and without sawdust, respectively. Our results show that rapidly establishing a perennial plant community may be more important than reducing initial resource availability when trying to limit invasions of resource-rich restorations.