Spatio-Temporal Boundary Dynamics in an East Central Indiana Tallgrass Prairie Reconstruction

The spatial and temporal dynamics of ecological boundaries reveal insight into interspecific competition, species responses to anthropogenic and natural factors, and ecological function. During a fifteen year study, spatial analysis of species composition was conducted across a plant community boundary in a tallgrass prairie reconstruction in East Central Indiana (USA). Boundary formation appeared to have been influenced by short-term flooding that inundated lower portions of the study site shortly after initial seeding in spring 1993. During the first growing season, a plant boundary was perceived to be located along the flood line. In general, the flood zone was dominated by weedy unsown-species, whereas the adjacent upland area, located above the flood line, was dominated by sown-species. The purpose of the current study was to track boundary movement and analyze spatial change by assessing the associated changes in species composition along an elevation gradient. Permanent monitoring transects and a topographic grid were positioned over the apparent boundary and sampled periodically from 1993 to 2010. Sampling included estimated percent areal cover and density for all plant species. Ordinations of topographic grid data sets indicate that the boundary has shifted and become more diffuse, in a way that was interpreted as a directional transition. The association of changes in species composition with changes in elevation appeared to weaken over time. Overall, the results indicate that sown-species expanded down-slope into areas previously dominated by weedy unsown-species, thus suggesting a possible competitive advantage by sown-species under the current management regime