Remotely-sensed indicators of burning efficiency of savannah and forest fires

Abstract

The objective of this study was to test remotely sensed indicators of burning efficiency for savanna and forest fires in Central Africa. The timing of fire with respect to vegetation senescence, the rate of post-fire recovery of vegetation and the spatial pattern of burning were potential indicators of burning efficiency. Statistical analyses were conducted to assess whether the values of a vegetation index (NDVI) and surface temperature ( T s ) were different at different stages of the burning season for burnt and unburnt areas, fragmented and continuous burnt patches, and early and late fires. Results show that fires affect areas with the lowest NDVI and highest T s values. Continuous and fragmented burnt patches are associated with vegetation covers in different states prior to a fire. The rate of recovery of vegetation after a fire depends on ecotypes (periforests recover more slowly than savannas), burning intensity and completeness (areas affected by fragmented burnt patches recover more quickly than areas affected by continuous burnt patches) and timing of the fire (areas affected by early fires recover more quickly than areas affected by late fires). The results suggest that combustion efficiency is lower for fragmented burnt areas compared to continuous burnt areas. It would thus be possible to decrease uncertainties in estimates of trace gas emissions from fires by replacing fixed burning efficiency values in emission models by values that would vary in space and time, based on measures of the spatial pattern of burnt areas as detected by remote sensing.