The positive association between high-frequency, low-intensity surface fires and the high levels of species richness in longleaf pine ecosystems is well documented. Recent studies have demonstrated additional linkages between specific fuel assemblages and fire intensity at small spatial scales. In this study we build upon both of these findings by using long term data sets to examine the relationship between fire and specific fuel types, and how the combination of these two elements contributes to ground cover species diversity. We used 11 years of monitoring data from forested longleaf pine stands to parameterize a structural equation model (SEM) examining causal relationships between fuels, fire history, and ground cover plant diversity. We then utilized another SEM to examine linkages between remotely sensed LiDAR data and the specific fuels used in the first SEM to indicate where fuels originate within various strata of the forest.
We found that four common ground fuel types; pine needles, pine cones and other 10-hour woody fuels, saw palmetto litter, and grass litter each contributed to the positive association between fire and plant species richness. The recent burning of overstory derived fuels, including pine needle litter, pine cones and other 10-hour woody fuels, had the greatest positive impact on diversity. Saw palmetto and grass litter also exerted a positive, yet smaller effect on diversity. Pine needle litter was positively associated with overstory LiDAR as was saw palmetto litter with surface LiDAR. Our parameter estimates for causal relationships between easily measured variables and plant diversity will allow for development of management models at the stand scale while informed by fuels measured at the plot scale.