Effects of dominant grass removal on plant diversity in restored tallgrass prairie

A common outcome of tallgrass prairie restorations is the successful establishment of the dominant C₄ grasses, while richness and abundance of forb species are often slow to recover leading to low plant diversity in restored communities.  In order to enhance the diversity of restored grasslands, it may be necessary to incorporate management strategies that reduce the dominance of C₄ grasses.  In order to determine if competitive interactions with the dominant grasses limit forb diversity, we established an experiment where two dominant grasses Andropogon gerardii or Panicum virgatum were physically removed from plots through clipping and foliar herbicide application.  Abundance of each species was reduced by either 50% or 100% relative to unmanipulated control plots.  In the control plots, A. gerardii was the most abundant grass with cover values up to 80%, while P. virgatum had cover values up to 40%.   Removing A. gerardii significantly increased light availability, and over two growing seasons increased percent forb cover (p = 0.0489), forb biomass (p = 0.0445), species richness (p = 0.0181), species evenness (p = 0.0249), and species diversity (p = 0.0063) compared to unmanipulated control plots, while removing P. virgatum did not significantly affect these parameters.  In conclusion, after two growing seasons it appears that competitive interactions between the dominant grasses and forb species do limit forb cover, forb abundance, and plant community diversity in this restored tallgrass prairie.  Future measurements will focus on longer-term responses to dominant grass removal, including recruitment of new forb species.