Mass and Energy Transfer Within and Between Burned and Unburned Savanna Environments

Abstract

Energy fluesand transfer resistances in burned and unburned savannas of the Orinoco Llanos were comparatively evaluated using the energy balance approach. It was found that after burning, the atmospheric transfer features of the savanna were changed as the net flux of long wave radiation increased from 6.192 to 7.692 MJm2day-' and therefore less energy was available at the surface. Net radiation in the burned and unburned savannas was mainly dissipated as sensible heat (76- 74 percent) and even though the burned and unburned savannas present constrasting surface properties, energy partitioning was similar in both plots because the relative greater aerodynamic resistance occurring at the burned savanna was compensated by the strong temperature stratification under the bare soil conditions. Thus, bouyancy generated turbulence in the burned savanna provived a 3 times greater mixing as compared to the roughness generated turbulence in the unburned savanna. The micrometeorogical measurements at the leading edge between the burned and unburned savannas evidenced horizontal heat flux as advection ( 1.458 MJm-'day-') when the air moved from the smooth and hot bare soil to the rougher and cooler vegetated surface.