Understanding responses of both dominant and sub-dominant plant speciesto management regimes and climatic variables is a critical component ofunderstanding an ecosystem's potential response to local or regional changes insuch parameters. The dominant vegetation of much of the North Americantallgrassprairie is composed of C4 grasses. As the most abundant species,Andropogon gerardii has been well characterizedecologically. The second most abundant, co-dominant species,Sorghastrum nutans, has received less attention, mainlybecause it has been considered the “ecological equivalent” ofA. gerardii and is assumed to have responses similar tothose of A. gerardii. The objective of this study was toassess the validity of this assumption by examining long-term abundancepatternsand responses to climate, fire, and grazing for both species. Based on 15 years(1983–1997) of plant species composition and cover data collected atKonzaPrairie Biological Station in northeastern Kansas, USA, we were able to detectimportant differences between these two grasses. Regression analysis showedthatlong-term reductions in the cover of A. gerardii werecorrelated with decreasing summer maximum temperatures, whereas inter-annualvariations in the cover of S. nutans were related toannualprecipitation. Additionally, the cover of S. nutansincreased with increasing fire frequency, while the cover of A.gerardii was not significantly affected by fire frequency. Bisongrazing did not significantly affect the cover of either species studied. Themean cover of A. gerardii decreased significantly over the15 years, but only a slight change was noted in the cover of S.nutans. The decrease in A. gerardiicorrespondedto increased plant species diversity and evenness and has the potential toimpact the tallgrass prairie ecosystem from population through ecosystemlevels.The observed differences in these co-dominant species may prove important underclimate change scenarios predicted for the tallgrass prairie of North America.