Multiple population sources of species for use in prairie restoration exist, including cultivars and non-cultivars of dominant native grasses. However, little is known about the competitive equivalency of different population sources of dominant C4 grasses and whether intraspecific variation in their competitive effect on the community might scale up to affect ecosystem assembly.  In 2005, we established an experimental restoration in a former agricultural field using cultivars and non-cultivars of the dominant grasses and two different species pools of non-dominant species containing equal richness and distribution among functional groups. We evaluated intraspecific variation in the competitive equivalency of Andropogon gerardii, Sorghastrum nutans, and Schizachyrium scoparium in terms of community response to individual and complete (all three species) removal of these dominant grasses. The competitive effect of each grass species and population source was determined from the difference in above ground net primary productivity (ANPP) between removal and control plots for forbs, non-dominant grasses, and all species other than the dominant grasses.

Results/Conclusions After the first growing season following removal of targeted dominant grasses, community differences were found between cultivar and non-cultivar sources of Sorghastrum nutans in terms of forb ANPP and between A. gerardii and S. nutans of the non-cultivar source measured by ANPP of all species other than the dominant grasses. Forb ANPP responded positively to removal of S. nutans cultivars, but forb ANPP decreased in response to removal of S. nutans non-cultivars (P= 0.022).  Comparison of competitive equivalency of the grass species showed that ANPP of all species other than the dominant grasses responded differentially to removal of non-cultivars of A. gerardii and S. nutans; community ANPP increased in response to removal of A. gerardii, but decreased in response to the removal of S. nutans (P=0.013).  In all cases, responses were consistent across species pools. Although A. gerardii and S. nutans are functionally similar, our results indicate the two species and source populations of each species are not competitively equivalent. Thus, dominant grass species and their population sources may function differently as biotic filters on community and ecosystem assembly during restoration.