Scheduling Prescribed Burns for Hazard Reduction in the Southeast

Twelve-year studies in the southeastern Coastal Plain revealed that pine stands should be burned every three years to reduce natural fuels and thus forestall damage from possible wildfires. Rates of overstory growth were not significantly different in burned and unburned stands. Guidelines for prescribed burning of pine stands in this region are presented. Southern pines are resistant to fire because their cambiums are insulated by thick bark and their crowns can withstand repeated scorching. However, pines cannot survive when their branch tips are killed by the wildfires that develop in tall, heavy understories and litter accumulations. From their inceptions, pine stands in the Southeast are plagued by the threat of such wildfires. · Even if a freshly harvested area is burned to remove the slash, the grass and herbaceous vegetation that immediately colonize the area form a fuel complex that can destroy young pines if a wildfire develops. By the time grass fuels have been shaded out, there is often a heavy accumulation of dead needles from which wildfires of tremendous intensity can develop if conditions are right. When crown closure is complete, accumulation rates increase. As much as 16 tons of surface fuel per acre may accumulate in 18-year-old plantations of slash pine (Pinus elliottii Engelm.) with 5by 10-foot spacing. 1 The presence of a tolerant understory and needle drape also brings the heat of a fire closer to the overstory. In the Coastal Plain, understory plants such as saw-palmetto (Serenoa repens Bartr. Small) and large gallberry (flex glabra (L.) A. Gray) are extremely flammable when preheated by burning ground litter, even though they remain green all year. Prescribed burning to reduce hazardous accumulations of fuel has been used for many years in pine forests of the Southeast; but the burns-conducted at intervals of five years or more-are usually too infre1Froelich, R. C. Effects of prescribed burning on the establishment and spread of Fornes annosus. /969. (Progress report FS-S0-2303-70.5 onjile at South. Forest Exp. Sta., Gulfport, MS.) March 1975/JouRNAL OF FoRESTRY/143 quent to protect the overstory during the entire interval between burns. One of the few studies of the cause-and-effect relationship between wildfires and hazard reduction burns was conducted in the Coastal Plain of north Florida in 1959 (J). Results showed that an increase in age of rough (fuel accumulation) was accompanied by a general increase in the number, intensity, and-most significantly-size of wildfires. In roughs more than five years old, seven percent of the acreage burned each year, whereas only 0.10 percent burned each year in roughs younger than five years. The 12-year study reported here was conducted to determine experimentally the optimum interval between hazard reduction burns in the southeastern Coastal Plain. Burning Frequency Tested In 1958, two areas were selected for study-one in north Florida and the other in southeast South Carolina. The Florida area contained a natural stand of 45-year-old longleaf pine (Pi nus palustris Mill.); the South Carolina area was divided into two sites, one containing mature Iongleaf and the other mature loblolly (P. taeda L.) pine. All plots at the three sites were initially burned with backfires (against the wind).