Mounting interest in the effects of multiple interacting disturbances has been motivated by more frequent and severe natural disturbances and increased human demands. Forest disturbances may have long-lasting legacies, including altered physical site conditions and life-history strategies represented by residual species assemblages. Disturbance-mediated changes in biophysical site conditions may impact subsequent plant recovery and susceptibility to future perturbations. This study investigated how longleaf pine (Pinus palustris) woodlands that were differentially impacted by an April 2011 EF3 tornado and a subsequent salvage harvesting operation responded to a 2018 prescribed fire. Utilizing plot-level data collected in the summers of 2016, 2017, and 2018, we tested (1) how variation in biophysical site conditions influenced prescribed fire effects, and (2) how differential impacts of multiple disturbances influenced the distribution and diversity of plant assemblages. Multivariate analyses were used to detect spatiotemporal variation in floristic assemblages across sites differentially disturbed, which were interpreted in the context of species-specific life-history strategies and responses to singular and synergistic disturbance effects.
Results/Conclusions
Sites differentially impacted by wind disturbance and salvage harvesting exhibited noticeable differences in plant assemblages and physical site conditions. In 2016, unharvested wind-disturbed sites had the greatest plant diversity, which was reduced on salvage-harvested sites, and lowest on sites undisturbed by the tornado. Increased plant diversity was attributed to increased light availability and habitat heterogeneity generated by canopy tree mortality. Reduced plant diversity was attributed to salvage harvest-mediated reductions in habitat heterogeneity and resource availability associated with dead wood removal. Compared to unharvested wind-disturbed sites, salvage-harvested sites exhibited a 91% reduction in the volume of coarse woody debris. Although salvage harvesting may be used to reduce hazardous fuel loads, low-intensity prescribed fires in longleaf pine woodlands rarely consume coarse woody debris. Moreover, the composition and cover of fine fuels was relatively unaffected by salvage harvesting, and it is hypothesized that fire effects will be comparable across wind-disturbed sites harvested and unharvested. Consistent selective pressures of prescribed fire on plants with common life-history strategies may facilitate the convergence of seemingly disparate plant assemblages initially attributed to wind disturbance and salvage harvesting. However, a paucity of canopy-derived fine fuels may prevent the spread of prescribed fire on wind-disturbed sites.