PATTERNS OF COMMUNITY STRUCTURE DURING SUCCESSION IN TALLGRASS PRAIRIE

Patterns of species diversity are a product of many complex interactions that change during succession. The purpose of this study was to measure components of community diversity during succession in six experimental treatments: protected prairie, grazed prairie, once-plowed prairie, annually plowed prairie, abandoned field, and a replowed field. Phase-space analysis of ordination data is introduced as a means of assessing successional dynamics in communities. The phase-space analysis of DCA ordination revealed similar successional trajectories for the protected, once-plowed and annually plowed treatments and divergent patterns in the other plots. The degree and rate of change during succession varied among treatments long after experimental plowing ceased. Patterns of species density, species diversity, mosaic diversity, community heterogeneity, and dominance changed among treatments over time. Heterogeneity decreased on four of five successional plots, but it increased on the grazed treatment. Mosaic diversity showed no clear pattern among the treatments during succession. When data from the successional treatments were combined, the overall patterns were more complex. Heterogeneity fluctuated during succession in response to changes in species density. As species density increased, species diversity increased whereas heterogeneity and dominance decreased. Because of the temporal fluctuations in heterogeneity and the different components of community diversity, no simple monotonic model will adequately represent patterns of community structure during succession. By analyzing the complex components of structure at different spatial and temporal scales, it will be possible to more clearly understand patterns and mechanisms controlling diversity in plant communities.