Monday, November 13, 2006

Comparative Effects of Burning on Ecosystem Fluxes in Two Adjacent Tall Grass Prairie Pastures.

Geoffrey Doyle1, David Billesbach2, Herman Mayeux3, Margaret Torn4, and Marc Fischer4. (1) Science Applications International Corp, P.O. Box 68, Bldg E3160, Gunpowder Branch, Aberdeen Proving Ground, MD 21010, (2) Univ of Nebraska, 25 L.W. Chase Hall, Lincoln, NE 68583, (3) Grazinglands Research Laboratory, USDA-ARS, 7207 W Cheyenne St., El Reno, OK 73036-2144, (4) Earth Sciences Div, Lawrence Berkeley National Laboratory, One Cyclotron Rd MS 90-1116, Berkeley, CA 94720

In grasslands and prairies fire is seen as an important management tool, where burning generally increases net productivity, however, there have been few studies that quantify the effect of fire on the fluxes of carbon, water, and energy. In this study two side-by-side tallgrass prairie fields (~65 ha each) located in El Reno, Oklahoma at the USDA-ARS Grazinglands Research Laboratory, were chosen due to similar topography, grazing intensity and burn history. One field was burned on March 8, 2005, and two sets of eddy covariance instrumentation was deployed in both fields on March 9th as described in Billesbach, et al. 2004. Fast response instruments were read at 10 Hz and 30 minute fluxes stored. Monthly aboveground biomass was collected from ten 0.25m2 quadrats per field, samples were separated into functional types, dead and green fractions, and mass and leaf areas recorded. Six autonomous, solar powered LiCor LI-8100 soil flux systems were deployed, three per field, measuring soil respiration every 15 minutes. In 2005, early in the growing season, greater above ground live biomass, higher net ecosystem exchange (NEE, or CO2 flux) and latent heat fluxes were observed in the unburned pasture. Later, significantly greater productivity was observed (biomass and NEE) in the burned pasture compared to the unburned control. While the burned plot had considerably higher green biomass (dominated by perennial warm season grasses), after accounting for loss due to burning, net exchange in the burned plot was similar to but smaller than the cumulative NEE in the unburned plot.   Burning appears to have reduced net carbon uptake relative to the unburned plot in 2005. In 2006, these effects are difficult to discern due to chronic below average precipitation. Continued measurements will aide in the determination of changes to NEE in the burned vs. unburned tallgrass prairie.