Effect Of Spring Burning On The Surface Energy Balance In A Tallgrass Prairie

Spring burning of dead biomass in tallgrass prairie is a common practice that may influence heat and water vapor transport from the landscape. Bowen ratio methods were used to measure the surface energy balances and evapotranspiration (ET) from burned (B) and unburned (UB) prairie near Manhattan, KS, USA. Data were collected from day of year (DOY) 109–258, 1997 following fire on the B site on DOY 107. Early in the growing season, differences in albedo and surface conductance to water vapor transport (g_s, i.e., mulch effect) caused large variations in energy fluxes between B and UB sites. During a 44-day period immediately after the burn (DOY 109–152), albedo averaged 43% lower on the B compared with the UB site. Consequently, available energy (net radiation minus soil heat flux) was 8.6% higher on the B than on the UB site. The g_s during that time was over three times higher on the B site, a result of dead biomass removal by fire. During the same period, the daytime Bowen ratios averaged 0.79 on the B site and 2.89 on the UB site, with ET rates of 2.97 mm per day (B site) and 1.40 mm per day (UB site). By DOY 152, canopy growth had moderated differences in albedo and available energy between sites. However, g_s and ET remained higher on the B site between DOY 152 and 181. Green leaf area index averaged 71% higher on the B site, and was the primary cause for this mid-season effect (i.e., differences in transpiration). By DOY 182, the effects of the burn on energy fluxes were negligible. Cumulative estimates of ET during the 150-day period were 503 mm on the B site and 408 mm on the UB site, thus, burning increased seasonal ET by 23.3%. Results suggest that land management or environmental factors that affect dead litter, albedo, or green leaf area will have strong impacts on the water and energy balances of a grassland.