SOiL NUTRIENT AND MICROBIAL RESPONSE TO PRESCRaBED FIRE IN AN OAK-PINE ECOSYSTEM iN EASTERN KENTUCKY

Abstract--On the Cumberland Plateau, periodic fire may be necessary to maintain oak-dominatedstands on xeric ridgetops. However, thin organic horizons and nutrient poor soils may limit the beneficial effects of fire by further reducing nutrient pools. The USDA Forest Service has reintroduced fire to oak-pine ridgetops in the Daniel Boone National Forest in the form of single, late winter prescribed burns. Objectives of this study were to document effects of single prescribed fires conducted in March 1995 and March 1996 on soil nutrients and microbialbiomass. In 1996, forest floor mass was determined before and after fire. In 1995 and 1996, total and available nitrogen, total carbon, pH, extractable cations, and microbial biomass were measured pre-burn and throughout the year after burning on burned and unburned sites. Thirty-two percent of the litter layer (Oi) was combusted in 1996, while no loss of the Oe and Oa horizons was found. A transitory increase in available nitrogen was detected in burned mineral soils. Increases in pH by 0.2-0.3 units were measured in the burned organic horizons. Lower concentrations of extractable cations were measured in burned soils than in unburned soils. Fire had a positive effect on active bacterial biomass, but no effect on fungal biomass. Our study suggests that single, late winter prescribed fire had minimal effects on belowground resources in these ridgetopecosystems. Since repeated burning might be necessary to promote oak regeneration, future research must address the effects of repeated burning on soil resources. INTRODUCTION Complicating the use of prescribed fire in eastern Fire has played an integral role in maintaining oak-pine Kentucky is the problem of accidental and incendiary fire