Neighborhood interactions in a natural population of the perennial bunchgrassBouteloua gracilis.

We analyzed neighborhood interactions in a natural population of the perennial bunchgrass blue grama (Bouteloua gracilis). Space occupation by individual plants was characterized in terms of neighborhood size. Neighborhood size was defined as the area potentially 'available' to an individual, which included the basal area of the plant and the bare area closer to the edges of the plant than to any others. Geographic Information Systems (GIS) were used to describe space partitioning. Growing season performance was evaluated as a function of neighborhood area and neighbor size, controlling for focal plant size. The area of the neighborhood was significant in explaining the remaining variation of allometric relationships between basal area and current vegetative and reproductive performance. In contrast, current performance of focal individuals was not related to the average basal area or the sum of basal areas of adjacent neighbors. Growing season performance was apparently affected by plant spacing, suggesting that competition for spatially distributed resources occurs. The presence of relatively small plants in neighborhoods with a high proportion of bare soil is consistent with the view of a community composed of patches undergoing their own successional dynamics. Competition and disturbances seem to play an important role in this semiarid grassland.