Wood debris or "slash" pile burns are extremely hot, long duration fires used in forestry operations to reduce fire hazards and concentrate fire damage. In the Coastal Plain of southwestern Georgia, they have been produced as part of landscape-scale restoration projects with the goals of reconnecting longleaf pine stands and reestablishing native ground cover to serve as fuel corridors in prescribed fire management. Where hardwood tree removal is a component of restoration, unmarketable wood debris is generated that is often burned near the site of removal, within or adjacent to native plant communities. Such sites remain devoid of vegetation for up to one year after burn and pose a potential management concern because they are usually recolonized by weedy or even invasive species. Within the 9,000 ha preserve of Ichauway, our study objectives are to examine the localized effects of these extreme fires on vegetation recolonization and soil characteristics, and specifically to: 1) characterize fuel load, temperature, and duration of burns; 2) compare vegetation composition, physical and chemical soil characteristics, seedbank status, and mycorrhizal inoculum potential in burned and unburned sites; 3) determine the rate of recovery by evaluating a site chronosequence at 0 to 6 years since burn, and 4) determine the potential to reestablish native species through soil amendment treatments (seeds, seedlings, with and without native topsoil).
Results/Conclusions
We measured belowground temperatures for the duration of burn along the edges of 6 slash piles in 2007, and found temperatures lethal to soil biota (>60°C) to a soil depth of 30 cm. Elevated soil temperatures that are potentially biologically lethal (>40°C) were measured at depths of 50 cm, and persisted for more than 120 hours. Total soil P was up to 10 times higher at burn pile centers (top 10 cm) relative to adjacent unburned soils, primarily due to the presence of hardwood ash. Total P remains elevated at least 6 years post-burn, as does soil pH. Measures of soil bulk density did not differ between burned and unburned sites, indicating that hardwood removal operations did not compress soil. Results of soil seedbank germination verify significant seed mortality in burned sites, and levels of arbuscular mycorrhizal inoculum potential are diminished significantly in the year after burn. Slash pile burns have resulted in initial soil sterilization, and created soil nutrient changes that persist for at least 6 years.
