Fire and Nitrogen Cycling Studies

Research Team: Dr. Lindsay R. Boring (Director), Dr. Robert J. Mitchell (Scientist) and Dr. Joe Hendricks (Former Postdoctoral Associate and Associate Professor, State University of West Georgia)

Fire is an important ecological influence that regulates the structure and function of longleaf pine ecosystems, including potential nutrient controls on productivity, forest floor and groundcover nutrient pools, and nutrient availability. Fire also can potentially result in significant losses of carbon, nitrogen, and perhaps phosphorus, but the extent to which burning regimes affect fire characteristics and subsequent nutrient fluxes is variable and not well documented in longleaf pine ecosystems. One hypothesis addresses nutrient loss scenarios due to season of burn. It proposes that nutrient losses may be greater from fires conducted during the growing (lightning) season since live plant tissues have greater nutrient content for potential combustion. However, in addition to fire seasonality, the groundcover vegetation, pyrogenic litter mass, and fire return intervals may interact with climate and other fuel-related variables to provide strong controls over fire intensities and effects in longleaf ecosystems. Although some fire effects have been examined in longleaf pine, most investigations have not coupled nutrient responses with physical characterization of burns, and with litter and groundcover fuels. This approach would permit a more mechanistic understanding of fire effects on ecosystem processes. We have conducted field measurements to: 1) compare differences in fire temperatures between dormant and growing season prescribed burns in longleaf pine-wiregrass (Aristida beyrichiana) groundcover versus longleaf pine “old-field” (Andropogon spp.) groundcover, and among three pine needle litter-loading treatments (0x, 1x, and 2x); and 2) determine the differences in standing crop and losses of nutrients (N and P) in litter and vegetation of these two groundcover types from dormant versus growing season fires. An additional field study was also conducted to validate fuel and temperature relationships in undisturbed 1-3 year old litter.

Additional Information:

Wilson CA, Mitchell RJ, Boring LR, Hendricks JJ. Soil nitrogen dynamics in a fire-maintained forest ecosystem: results over a 3-year burn interval. Soil Biol Bio. 2002;34:679-689.

Hendricks JJ, Wilson CA, Boring LR. Foliar litter position and decomposition in a fire-maintained longleaf pine-wiregrass ecosystem. Can. J. For. Res. 2002;32:928-941

Hiers JK, Wyatt R, Mitchell RJ. The effects of fire regime on legume reproduction in longleaf pine savannas: is a season selective?. Oecol 2000;125:521-30.

Hainds, MJ, Mitchell RJ, Palik BJ, Boring LR, Gjerstad DH. Distribution of native legumes (Leguminoseae) in frequently burned longleaf pine (Pinaceae)-wiregrass (Poaceae) ecosystems. Am J Bot 1999;86:1606-14.

Wilson CA, Mitchell RJ, Hendricks JJ, Boring LR. Patterns and controls of ecosystem function across acoss a complex environmental gradient in longleaf pine-wiregrass savannas: II. Nitrogen dynamics. Can J For Res 1999;29:752-60.

Funded by: The Joseph W. Jones Ecological Research Center