Effects of Fire on Net Radiation and Evapotranspiration in a Mature Forest Plot in Para State, Eastern Brazilian Amazon

Abstract:

Forest fires are extremely harmful for the Amazon region, affecting the natural cycle of vegetation and ecosystem functioning. The effects of fire on net radiation and forest water cycling are not well understood, especially due to the difficulty of obtaining surface flux measurements in fire-affected areas with high temporal and spatial resolution. The present study aimed to characterize and analyse, using MODIS remote sensing data in combination with the SEBAL model, the temporal dynamics of net radiation and evapotranspiration in a 120 km² mature Amazonian forest plot affected by fire in September 2010 in the state of Para, Brazil. The analysis of the surface energy fluxes in the month before and in the month after the fire indicated a 25% and 27% decrease in net radiation and evapotranspiration, respectively. The average values of net radiation and evapotranspiration for the 3 years pre-fire were 119.3 W m^-2 and 1436.0 mm yr^-1, respectively. After the significant decrease was verified immediately post-fire, net radiation values increased at an average annual rate of 3% and evapotranspiration values increased at an average annual rate of 20%. In both cases, the highest increase in rates were verified one year after the fire, corresponding to 5% in net radiation and 58% in evapotranspiration. The average values of net radiation and evapotranspiration 3 years post-fire were 119.2 W m^-2 and 1382.6 mm yr^-1, respectively, which are quite close to the average values verified prior to burning. Thus, we conclude that 3 years was enough time for this forest plot to recover its original state in terms of surface fluxes. Despite this result, it is important to note that a high severity fire can alter the canopy characteristcs more strongly than a low severity fire, which means that distinct disturbance regimes will affect the energy fluxes after the fire in forested areas quite differently.