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 th at may influence heat and water vapor transport from the landscape. Bowen r atio methods were used to measure the surface energy balances and evapotran spiration (ET) from burned (B) and unburned (UB) prairie near Manhattan, KS , USA. Data were collected from day of year (DOY) 109-258, 1997 following f ire on the B site on DOY 107. Early in the growing season, differences in a lbedo and surface conductance to water vapor transport (g(s), i.e., mulch e ffect) caused large variations in energy fluxes between B and UB sites. Dur ing a 44-day period immediately after the burn (DOY 109-152), albedo averag ed 43% lower on the B compared with the UB site. Consequently, available en ergy (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, th e 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). B y 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 be tween DOY 152 and 181. Green leaf area index averaged 71% higher on the B s ite, and was the primary cause for this mid-season effect (i.e., difference s in transpiration). By DOY 182, the effects of the burn on energy fluxes w ere negligible. Cumulative estimates of ET during the 150-day period were 5 03 mm on the B site and 408 mm on the UB site, thus, burning increased seas onal ET by 23.3%. Results suggest that land management or environmental fac tors that affect dead litter, albedo, or green leaf area will have strong i mpacts on the water and energy balances of a grassland. (C) 1999 Elsevier S cience B.V. All rights reserved.