Response of longleaf pine forests to fire and fire surrogate treatments for wildfire hazard mitigation and ecological restoration

Longleaf communities of the Gulf Coastal Plains historically had a low intensity frequent fire regime, i.e. every 2 to 4 years. This produced a longleaf-dominated overstory with other southern pines and occasional hardwoods and an herbaceous dominated understory. A period of fire control allowed hardwoods to increase in the mid and overstory layers while woody shrubs gained understory dominance. Research was conducted in cooperation with Auburn University at the Solon Dixon Forestry and Education Center near Andalusia, Alabama as part of the national Fire and Fire Surrogate Study. The principal objective was to quantify the plant community responses to: (1) fire exclusion in the untreated control, (2) prescribed fire, (3) thinning, (4) thinning plus prescribed fire, and (5) herbicide plus prescribed fire. Selected stands were thinned early in 2002 followed by prescribed burns in April and May. Herbicide treatments were done in fall 2002 and those stands were burned the following spring. A second set of prescribed burns was applied to burn and thin plus burn treatments during the early growing season 2004.The mechanical thinning treatment targeted other pines and hardwoods, reducing them by 60 percent in the overstory. Burning alone resulted in no change in midstory hardwoods while thinning reduced their density significantly. The cover of understory shrubs and woody vines was reduced temporarily by burning but only the herbicide and burn treatment resulting in a lasting change. Understory forb cover increased after all disturbances with an additive effect from thinning and burning. Grasses responded positively to the reduction in overstory density and to burning when combined with the thinning. Thus, thinning is the quickest method of readjusting overstory and midstory structure and composition, while providing the open space needed for grasses. Fire is also needed however, to control larger understory hardwoods and to further increase grasses and forbs.