The impact of wildfire on the land surface parameters of a semi-arid grassland in the southwestern U.S.

Abstract

Just before the installation of a long-term energy/carbon flux tower site at the 10,000-acre Appleton-Whittle Research Ranch in southern Arizona, a wildfire burned nearly 90 % of this semi-arid grassland area in the region and there was little vegetation remaining on the surface. Wildfires in this region occur roughly every 7 - 15 years. The establishment of the site allowed for the determination of recovery time for this semi-arid grassland ecosystem. We examined how the wildfire altered the land surface characteristics such as broadband and photosynthetically active radiation (PAR) albedo, surface roughness, and the seasonal net ecosystem exchange. This information was also used to determine the amount of time it took this ecosystem to recover back to a quasi-baseline state. We found that it took approximately 3 years for the surface roughness to increase from 0.04 to 0.12 m, and then stay near that level in the following years. The monsoon season (July - September) net ecosystem exchange (NEE) was positive (source) for two years following the wildfire and did not become a significant net carbon sink until 2005. The ecosystem recovery from this wildfire event may have occurred sooner but the accumulated rainfall for the 2 years following the fire were both well below the 20-year average of 254 mm. We were also able to determine that immediately after the wildfire, the soil shortwave and PAR albedo was 0.20 and 0.13, respectively. However, with the onset of the monsoon and rainfall, both the shortwave and PAR albedos decreased to 0.10 and 0.07, respectively. The albedos reverted to the original values after several days of no additional rainfall.