Overstory Species Dominance Impacts Soil Fertility in Frequently Burned Coastal Plain Pine (Pinus spp.) Forests: A Case Study from the Zuni Pine Barrens, Virginia, USA

Prior research on the effects of frequent fire in Coastal Plain pine forests of the mid-Atlantic and southeastern US has highlighted how even slight variations in species composition may correspond to fluctuations in nutrient cycling. We compared pH, carbon-nitrogen ratio (C:N), calcium (Ca), magnesium (Mg), phosphorus (P), and potassium (K) for four forest stands in the Zuni Pine Barrens Preserves of Virginia. These sites are consistent in terms of soil composition, but differ in terms of fire regime and dominant overstory species (frequently burned and dominated by Pinus taeda, P. palustris, or P. serotina, or infrequently burned mixed pine-hardwood). Our results suggest that stand composition and species dominance do play a significant role in mediating soil fertility, especially pH and the relative abundance of C and N. After almost thirty years of frequent prescribed burning (every 2-3 years), we observed significantly lower levels of Mg, K, and P in the O Horizon and mineral soil of the frequently burned pine-dominated stands when compared to the infrequently burned mixed pine-hardwood stand. Interestingly, we found that dominance by P. palustris (longleaf pine) with frequent fire was associated with unique soil and detrital characteristics, with elevated C:N and pH compared to the infrequently burned stand, as well as to stands dominated by P. taeda and P. serotina. Our results provide useful context to the varying effects of species dominance on soils under differing prescribed fire regimes.