Fire frequency and soil enzyme activity in southern Ohio oak-hickory forests

As part of a larger study of the efficacy of prescribed fire for restoration of structure and function in deciduous forests subjected to fire suppression and chronic atmospheric deposition, this study examined the effects of annual and periodic fire on soil organic C and the activity rates of four soil enzymes (acid phosphatase, beta-glucosidase, chitinase, and phenol oxidase) over a 5-year period. Two study areas in southern Ohio were divided into watershed-scale treatment units of 90-120 ha. One unit in each site was burned annually between 1996 and 1999, a second burned periodically (1996 and 1999) and a third left as an unburned control. Relative to the unburned control, acid phosphatase and beta-glucosidase activities decreased in the burned plots, by 15-50% and 5-50%, respectively. Phenol oxidase activity increased 20-80% following burning, depending on site. Chitinase activity changed little. Taken together these changes indicate a shift in these ecosystems back to a condition characterized by relatively slow nutrient recycling, low microbial activity and recalcitrant organic matter, much like what is believed to have existed prior to a century of atmospheric deposition and fire suppression. These results suggest that prescribed fire can be a significant aid in restoring mixed oak forests to pre-settlement conditions. (C) 2003 Elsevier Science B.V. All rights reserved.