Grasslands consist of a matrix of a few dominant grasses which structure the environment, affecting the composition and abundance of the sub-dominant species that are responsible for making up the diversity of grassland communities.  Historically, tall grass prairies were dominated by one to three native C₄ warm season grasses (i.e. Andropogon gerardii, Schizachyrium scoparium, and Sorghastrum nutans).  However, Poa pratensis and other non-native C₃ grasses are increasing in abundance and in some areas are replacing the native dominant grass species.  Previous studies have examined the static relationships between dominant species identity and diversity of the sub-dominant plant community; lower species richness associated with dominance by non-native species relative to dominance by non-native species.  This study takes a dynamic perspective and examines the relationship between dominant species identity and succession rates in old field communities using a long term chronosequence data set of 19 abandoned agricultural fields (old fields) at Cedar Creek Natural History Area.  Each field contains 100 1.0 X 0.5m plots (N=1900).  Plant cover data was collected at the plot level for 6 years (1983, 1989, 1994, 1997, 2002, and 2006).  We calculated Euclidean distance (a quantitative dissimilarity metric) using relative percent cover values for each plot for all time lags.  We plotted Euclidean distance against time lag and then compared the rate of succession between plots with different dominant species.  

Results/Conclusions

There was a significant effect of dominant species identity on succession rate.  Andropogon gerardii was found mainly in the older fields where the plant communities are approaching a more stable state and as a result dominance by A. gerardii was associated with a slower rate of succession.  Agropyron repens was mainly found in the younger fields that experience high rates of species turnover and therefore, dominance by A. repens was associated with faster rates of succession.  Poa pratensis and S. scoparium are found in fields of all ages, yet there was a significant difference between succession rates in plots dominated by P. pratensis versus plots dominated by S. scoparium.  Dominance by P. pratensis was associated with a significantly slower succession rate compared to dominance by S. scoparium.