Mineral Soil Chemical Properties as Influenced by Long-Term Use of Prescribed Fire with Differing Frequencies in a Southeastern Coastal Plain Pine Forest

Recent studies suggest increased fire frequency may impair soil chemistry, but few studies have examined long-term effects of repeated, frequent prescribed fires on forest soil properties in the southeastern Coastal Plain, USA. In this study, forest soil chemistry at the 0⁻10 and 10⁻20 cm mineral soil depths of sandy surface horizons (Entisols and Spodosols) were compared among units burned 0, 4, 6, and 8 times between 2004 and 2015 and 0 and 20 times between 1978 and 2015 in a longleaf (Pinus palustris Mill.)⁻loblolly (Pinus taeda L.) pine savanna at the Tom Yawkey Wildlife Center (Georgetown, SC, USA). At the 0⁻10 cm soil depth, soil pH (p = 0.00), sulfur (p = 0.01), calcium (p = 0.01), iron (p < 0.01), manganese (p < 0.01), and aluminum (p = 0.02) treatment means differed (2004⁻2015). Calcium and manganese displayed positive, significant relationships and sulfur displayed a negative, significant relationship with increasing fire frequency (p < 0.05). However, correlation of these relationships was low (r2 ≤ 0.23). Using linear contrasts to compare the mean of all fire treatments (20 fires from 1978 to 2015) to the mean of the unburned compartment, sulfur (p = 0.01) and iron (p < 0.01) were less in soils from the burned compartments. At the 10⁻20 cm soil depth, soil pH (p = 0.01), manganese (p = 0.04), phosphorus (p = 0.01), potassium (p = 0.02), and iron (p < 0.01) treatment means differed (2004⁻2015). Potassium displayed a negative, significant relationship and soil pH displayed a positive, significant relationship with increasing fire frequency (p < 0.05). Correlation of these relationships was low (r2 ≤ 0.16), however. Using linear contrasts to compare the mean of all fire treatments (20 fires from 1978 to 2015) to the unburned compartment, potassium (p = 0.00) and iron (p < 0.01) were less in soils from burned compartments. These results are inconsistent with studies suggesting that forest soil chemistry is substantially altered by increased fire frequency and support other studies from this region that have documented minimal or temporary soil chemical changes associated with frequent prescribed fires