Plant community structure and stability over ten years of warming and harvesting

Background/Question/Methods: Plant species cover and biomass have been assessed three times a year since 2000 in a field warming and clipping experiment in central Oklahoma as part of a larger experiment to assess the effects of climate warming and land-use on the tallgrass prairie ecosystem. Results/Conclusions: NMS ordination with blocked MRPP were performed on maximum annual cover for each species. These analyses found significant effects due to clipping on community structure in 2005 (a dry year), significant effects of both warming and clipping in 2006 (a normal rainfall year), and no significance of warming or clipping in 2007 (a very wet year). Clipping significantly increased species richness and evenness, while warming tended to decrease richness and evenness. Diversity was not related to biomass production; however biomass stability (CV) was positively correlated to species richness. C4 plant biomass and cover has been greater in warmed plots since 2001. Analysis of individual species shows that of the dominant C4 perennial grasses, Sporobolus compositus did not contribute at all, Schizachyrium scoparium contributed slightly, and Sorghastrum nutans contributed most to the difference in C4 cover between warmed and unwarmed plots. No other functional groups showed consistent directional changes due to treatments over the ten years. While there is a significant response of C4 species as a whole, individual species may respond differently from their functional group. Most other climate change experiments have not examined overall community structure but do find species-specific responses to treatments. Experiments in the arctic are currently the only other studies able to make any generalizations regarding species responses and functional groups. They also find species-specific responses within functional groups that show a directional response.