Influences of fire intensity on vegetation cover and local biodiversity in species-rich pine savanna groundcover

High frequency lightning-season fires maintain high biodiversity in pine savannas.  We explored the influence of fire intensity and other variables on groundcover structure in pine savannas of southeastern Louisiana.  Pine savannas historically covered most of the Gulf Coastal Plain until anthropogenic disturbance reduced them to < 2% of their original extent.  We experimentally manipulated fire intensity by altering natural fuel loads:  reduced, un-manipulated and increased.  We assessed effects on total vegetation cover, large-stature grass cover, and species richness.  Our measures of fire intensity were maximum temperature, total heat produced, and duration of elevated temperatures above ambient levels.  Fuel loads directly influenced fire intensity (highest in fuel-addition plots).  Increased fire intensity in turn directly affected groundcover plants.  Pre-treatment cover and mean species richness were similar across treatments.  Five months after prescribed fires mean cover was highest in fuel removals (85%) and lower in controls (78%).  In fuel addition plots mean cover was reduced to 48%.  Mean cover of tall-stature grasses was highest in fuel removals and lowest in fuel additions.  Where we reduced fuels we found the highest mean species richness (26).  Species richness in controls was intermediate (23).  In fuel additions we found the fewest species on average (19).  As our study continues we will test predictions concerning assembly rules and dispersal limitation on recovery among plots that experienced differences in fire intensity that differentially affected plant cover.  Results to date suggest that these mechanisms interact to determine the structure and composition of local pine savanna groundcover assemblages.