Community Assembly and Vegetation Patterns across Space and Time in the Longleaf Pine Ecosystem

Disturbance is an important factor that shapes plant community structure in firedependent grasslands, and alteration of disturbance regimes can have large consequences on species richness and species composition. However, the response of vegetation to disturbance may change with environmental context. I re-sampled 59 permanent vegetation plots in the longleaf pine ecosystem twenty years after they were established to determine the magnitude of vegetation change at a range of spatial scales (0.01 m2 to 1000 m2). I was interested in how environmental context and fire frequency concurrently influence vegetation change over time and if those relationships change with spatial scale. I quantified the magnitude of vegetation change using two different metrics of beta-diversity (beta turnover, the proportion of species turning over and Bray-Curtis dissimilarity, an abundance-weighted metric) and by tabulating changes in species richness. The magnitude of vegetation change was highly dependent on environmental context and fire frequency. Changes in species richness, beta turnover, and BrayCurtis dissimilarity were greatest on silty, frequently-burned sites, whereas most sandy, infrequently-burned sites remained stable. Furthermore, the amount of change detected was scale-dependent. Species richness increased at larger spatial scales over time, but decreased at the two smallest spatial scales. In contrast, beta turnover and Bray-Curtis dissimilarity decreased with increasing spatial scale, suggesting that there is greater stochasticity at small scales.