Dynamics of nitrogen competition between successional grasses

Pairwise competition experiments were performed for 3 yr on an experimental N gradient at Cedar Creek Natural History Area, Minnesota, where N is the major limiting resource during early succession. Agrostis scabra, an early successional grass, competed against another early (Agropyron repens), a later (Schizachyrium scoparium), and an even later (Andropogon gerardi) successional species. On low N soils, Agrostis was competitively displaced by each of the later successional species, but persisted with Agropyron. On high N soils, Agrostis was displaced by all 3 other species. The inferior competitive ability for N of the early successional species refutes the resource ratio hypothesis of succession. Rather, the high allocation of Agrostis to seed and its rapid colonization of fields support a colonization-competition hypothesis of succession. -from Authors