INFLUENCE OF SOIL AND PLANT-PLANT INTERACTIONS ON GROWTH AND FLOWERING OF TWO POTENTIALLY DOMINANT BUNCHGRASSES IN THE LONGLEAF PINE ECOSYSTEM

Neighborhood interactions and edaphic conditions can help predict the distribution of species and the composition and structure of plant communities. The longleaf pine ecosystem of the southeastern U.S. provides an ideal setting in which to study interactions among dominant members of the understory community. Bunchgrasses provide the structure and fuel that enable frequent fires to mediate succession and maintain the extremely diverse understory community characteristic of the imperiled longleaf pine ecosystem. I investigated responses to bunchgrass neighborhood composition by wiregrass (Aristida stricta Michx.) and little bluestem (Schizachyrium scoparium [Michx.] Nash), two competing and potentially dominant C4 bunchgrasses occurring in north Florida longleaf pine savannas. I conducted (1) a reciprocal transplant experiment and (2) a multi-factorial greenhouse experiment to better understand how these two species influence each other in the context of their neighborhoods and their native soils. I asked: (1) What is the effect of these two species interacting with each other in neighborhoods in determining the performance of both species? (2) What is the effect of edaphic conditions in determining the performance of the two species? And lastly, (3) how do neighborhood composition and edaphic conditions interact to influence bunchgrass performance and potential dominance of the two species? Overall, bluestem individuals grew faster, produced more total biomass, more aboveground biomass and more flowering culms than wiregrass, although wiregrass produced more belowground biomass. In the greenhouse, conspecific competition was more intense for both species. The two species responded differently to conspecific crowding in terms of biomass production, with bluestems decreasing in aboveground biomass with additional conspecific neighbors, while wiregrass decreased in terms of belowground biomass production with additional conspecific neighbors. Overall our findings suggest that wiregrass may compete more in terms of belowground biomass production, while bluestems respond competitively in terms of aboveground resource allocation. A lack of variation in soils among sites indicates that the edaphic condition we assessed does not determine bunchgrass dominance in these sites