Wildfire is a primary control of forest succession patterns and carbon cycling in the boreal forest. Under a global warming scenario, fire activity in this region is expected to increase, releasing stored CO2 to the atmosphere and potentially changing a region which is now a primary sink for terrestrial carbon into an equally significant source . The dominant controls on carbon uptake and emission are soil temperature and moisture; both of these factors can change radically following fire disturbance. This paper will discuss initial results from a study to monitor changes in soil thermal and moisture conditions following wildfire and the effect that these changes have on carbon emissions from the soil.
More than 40,000 hectares outside of Tok, Alaska (63o 18' N latitude, 142o 45' W longitude) burned in a series of wildfires during July and August of 1991. The study area is located on the outwash plain of the Tanana River on essentially flat slopes with an average elevation of 500 m. Paired burned and unburned sites have been established along a moisture gradient within the three major soil-vegetation complexes found at Tok: 1) black and 3) aspen on well-drained sandy silt.
During the 1996 growing season, intensive measurements of temperature and moisture content will be made in soil profiles within each of major soil-vegetation sites using thermistors and Time Domain Reflectometry (TDR). Initial temperature measurements made in 1995 clearly show warmer temperatures in burned soils regardless of soil drainage or above ground vegetation Surface fluxes of CO2 at the profiles will be measured with a field portable CO2 meter (PP Systems, Hertfordshire, UK. CO2 concentrations are measured over a 2 minute period to provide both concentration (ppm) and flux (g/m2/hr). To represent spatial variability, 20 by 20 m grids have been established in each site. Measurements of all parameters will be made to the base of the organic horizons at each grid node. Data will be used to calibrate existing models which predict soil respiration as a function of temperature and moisture.
Katherine P. O'Neill Nicholas School of the Environment Duke University Durham, NC 27708 Telephone: (919) 613-8048 E-mail: kpo@acpub.duke.edu