Longleaf pine (Pinus palustris) savannas of the North American Coastal Plain are known for having a tree component that regenerates in patches of even-aged individuals within gaps, resulting in an overall uneven-aged population structure. However, mechanisms maintaining this structure are poorly understood. Using long-term monitoring data in native and post-agricultural pine savannas, we present evidence for links among weather, prescribed fire patchiness, patterns of pine regeneration, and effects of regeneration patch age and environment on spatial heterogeneity in the plant community, fire behavior, and soil characteristics. Sources of data include an old-growth longleaf pine tree census from 1978-present, post-burn evaluations from 1995-present, post-burn mapping from 2005-present, and methods of analysis include corellation analysis, PerMANOVA, and logistic regression to test for associations among variables.
Results/Conclusions
The degree of burn patchiness on a given burn day is predicted by land use history and associated fuel type, local topography, time since previous fire, pine timber stocking, season of burn, relative humidity, and drought indices. While some patch locations recur in association with topographic features or forest stand characteristics, others are ephemeral and suggest a feedback loop in which accumulated fuel increases the likelihood of subsequent burning. This is particularly true where pine species become established and deposit flammable fuel. In an old-growth setting, longleaf pine is preferentially recruited in unburned patches, as well as open areas and where canopy trees have recently died, resulting in initially dense clusters that persist for over two centuries. Presence and age of regeneration patches influences the presence of certain plant taxa, especially plants in the families Asteraceae and Fabaceae, as mediated by changes in light, fire severity, and soil chemistry and bulk density. These links provide important insights into the natural ecosystem function of longleaf pine savannas and the role of heterogeneous patterns of fire severity. The results also provide guidance for the application of prescribed fire, including conditions under which patchy burning can be accomplished, for the perpetuation and restoration of native longleaf pine savannas.