Competitive equivalency of cultivar and non-cultivar dominant prairie grasses in an experimental restoration

Background/Question/Methods

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 scales to affect ecosystem assembly.  In 2006, 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 of species among functional groups. We evaluated inter – and intra-specific 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. Removals were maintained throughout each growing season though little maintenance was needed after the initial treatment. The competitive effect of each grass species and population source was determined from the difference in percent cover between removal and control plots for each dominant grass individually, forbs, non-dominant grasses, and legumes.

Results/Conclusions

After the second growing season following removal of targeted dominant grasses, no community effects were evident between the removal of cultivar and non-cultivar sources of the dominant grasses. However, interspecific differences in competitive equivalency of the dominant grasses were observed in terms of community response to their removal. Non-dominant grasses and non-planted forbs responded differentially to removal of the different dominant species (P = 0.003 and P = 0.056 respectively). Furthermore, the dominant grasses responded differentially to removal of their co-dominants (P < 0.05). For example, A. gerardii responded positively to S. nutans removal, whereas S. nutans showed a slightly negative response to A. gerardii removal. In all cases, responses were consistent across dominant grass source and species pools. Although A. gerardii, S. nutans, and S. scoparium are functionally similar as they are all dominant C4 grass species, our results indicate the species are not competitively equivalent. Thus, these dominant grass species may function differently as biotic filters on community and ecosystem assembly during restoration.