Impact of Interacting Disturbances on Longleaf Pine Communities

Abstract

Disturbance in longleaf pine (Pinus palustris P. Mill.) communities alters the structure, function, and composition of the forest. Species heterogeneity and diversity were investigated at the Escambia Experimental Forest located in Brewton, AL in an attempt to document spatial effects of past disturbance. To identify the short term effects of present disturbance, the interactions of harvesting, hurricane, and salvaging on the fuel complex were examined and fire intensity was determined during prescribed fires. Finally, understory community composition was related to post-disturbance variables. The heterogeneity and diversity indices were similarly affected by fire regime in the Escambia Experimental Forest over the past 55 years. Species diversity and heterogeneity increased with a longer fire return interval and decreased with a greater number of fires, indicating that more frequent fires could result in a homogeneous landscape. Fire intensity was a major determinant of post-fire effects and was influenced by variation in the fuel complex. The prescribed burns had maximum fire temperatures at a low range of 121-148°C and a high range of 288-315°C. Variance occurred at small block sizes along transects sampled in no harvest compartments and at moderate to high block sizes along transects in harvested compartments. Variance peaks were observed at several block sizes, indicating non-stationary patterns of gaps and patches. Along transects located in the “no harvest” compartments, litter depth explained 20% of the variability in maximum fire temperature, while variability along transects located in harvested compartments were explained by 10 and 100-hr fuels (28-33%). Community composition, following the multiple disturbances, was assessed using ordination techniques. Species covers, including Pityopsis graminifolia, Lespedeza procumbens, Solidago odora, Sasafrass albidum, Cornus florida, Andropogon spp., Aristida spp., Ilex glabra, Gaylussacia dumosa, Prunus serotina, Nyssa sylvatica, and Quercus falcata, were correlated with maximum fire temperature. Other species covers, such as Dichanthelium spp., Smilax spp., Ceanothus americanus, Carphephorus odoratissimus, Rubus spp., and Panicum spp., required bare soil to re-colonize. Species heterogeneity and diversity in longleaf pine forests are influenced by numerous factors modified by decades of natural and human-caused disturbance.