Effect of Thinning and Clear-cuts on the Transmission of Fire in Slash Pine Plantations during Restoration to Longleaf Pine

Restoration of the Pinus palustris (longleaf pine) bunch grass ecosystem that once dominated the southeastern coastal plain has become a goal for many managers on public lands. However, fire exclusion and conversion to Pinus elliottii (slash pine) plantations has provided the conditions for much of the forest to become susceptible to what Lindenmayer et al. (2011) call a “landscape trap,” where ecological processes no longer function to maintain the ecosystem. For the longleaf pine-bunchgrass ecosystem, the trap occurs when fire-dependent herbaceous vegetation have been replaced with woody shrubs, and there are no fine fuels that will readily transmit frequent fire. Restoration of slash pine plantations to longleaf pine forest will require continued transmission of fire across the restoration areas. With the cooperation of the US Forest Service, we conducted an experiment to study the effectiveness of thinning and patch clear-cuts in slash pine plantations and compared the burnability of these treatments. Eighty percent of the thinned plots burned, but only 12% of the patch clear-cuts did. These differences resulted from reduced needle cast in the clear-cuts. Plots in which the ground cover was dominated by herbaceous vegetation were significantly more likely to burn (97%) than those dominated by woody vegetation (38%). Plots without fire for eight years prior to the experimental burn did not burn across the clearcut patches that had no recent needle cast from canopy trees. Maintenance of the canopy is important in fire transmittal because fire allows longleaf pine restoration without expensive site preparation and groundcover reintroduction.