Stream nitrate response to different burning treatments in Southern Appalachian Forests

Abstract

Southern Appalachian forests are undergoing considerable change due to altered disturbance regimes. For example, fire exclusion has had a major impact on the structure and function of pine-hardwood ecosystems. Recently, fire has been prescribed for a variety of applications: 1) stand-replacement in the form of a mimicked wildfire, 2) site-preparation as part of a fell-and-burn prescription, and 3) understory burning for fuels reduction and wildlife habitat improvement. Assessing watershed-scale responses to burning requires identification of key parameters indicative of changes in structure and function. In the southern Appalachians, nitrogen in the form of NO₃ is a key indicator of ecosystem change or response to disturbance. We compared stream NO₃-N responses among stand-replacement fires (Winespring Creek and Hickory Branch), a fell-and-burn prescription (Jacobs Branch), and a wildfire in an old-growth deciduous forest (Joyce Kilmer). Nitrate-nitrogen concentration increased following two of the four fires. Concentrations following the fell-and- burn prescription fire increased from <0.01 to a maximum of 0.075 mg L^-1 and remained elevated for 8 months. Similarly, stream NO₃ concentration increased approximately 2 weeks following the old-growth deciduous wildfire from 0.04 to a maximum of 0.50 mg L^-1 and remained elevated for 6 weeks. There were no significant differences in NO₃ following one of the stand-replacement fires or between treatment and control or pre- and post-burn following the other stand-replacement fire due to maintenance of an unburned riparian area. Although the old-growth deciduous wildfire was essentially an understory burn, the magnitude of stream N response suggests that unavailable recalcitrant forms of N may have been released during the wildfire, as well as a reflection of the potential inefficiency of old-growth forests at sequestering mobilized nutrients. In all cases, hydrologic losses of NO₃-N were insignificant with respect to effects on water quality and site depletion of N.

Keywords

disturbance, ecosystems, nitrate response, old growth, North Carolina, prescribed fire, resistance, riparian zone, southern Appalachia, stream

Citation

Clinton, Barton D.; Vose, James M.; Knoepp, Jennifer D.; Elliott, Katherine J. 2003. Stream nitrate response to different burning treatments in Southern Appalachian Forests. Pages 174-181 in K.E.M. Galley, R.C. Klinger, and N.G Sugihara (eds.). Proceedings of Fire Conference 2000: The First National Congress on Fire Ecology, Prevention, and Management. Miscellaneous Publication No. 13, Tall Timbers Research Station, Tallahassee, FL