Soil Chemistry in a Loblolly/Longleaf Pine Forest with Interval Burning

We examined the 30-yr cumulative effects of prescribed fires at intervals of 1, 2, 3, and 4 yr in a loblolly and longleaf pine forest in the Coastal Plain of South Carolina. The fine fraction of the forest floor (Oe + Oa horizons) contained much more carbon and nitrogen per unit area in the control plots (1.7 and 0.05 kg/m² , respectively) than in the 1-yr burn interval plots (0.4 and 0.007 kg/m² , respectively). Mineral soils (0-0.2 m depth) were highly variable in chemistry, and showed only slight differences across the burning treatments for nitrogen and sulfur. No trends were apparent for phosphorus in the forest floor or mineral soil; differences in acidity and extractable cations were also slight. The nutrient content of foliage was generally low, with no differences across burning intervals. Our results are consistent with earlier studies that showed the biogeochemical effects of repeated surface fires in southern pine forests are generally limited to the forest floor, with the possible exception of overall reductions in nitrogen cycling.