Assessment and mapping of fire severity on rangeland in the fescue grass ecoregion of southwestern Alberta using resource satellite data, field observations, and digital terrain models

In December 1997, a 22,000 hectare wildfire spread through native foothills rough fescue grassland and forested grazing lease land in the strongly rolling topography of the Porcupine Hills southwest of Granum, Alberta. A study was initiated in the spring of 1998 to investigate the extent to which post-fire land cover, as determined using LANDSAT Thematic Mapper image data, could be used to indicate fire severity, and the extent to which fire severity was related to topographic variability. A post-fire land cover map was developed based on the normalized difference vegetation index. Field data and this map were used to create a fire severity map, which was combined with selected topographic variables derived from a digital elevation model. It was possible to map levels of fire severity using post-fire land cover; however, the presence of high amounts of green vegetative cover was not always indicative of low fire severity. Slope azimuth, elevation, and the interactive effects of slope azimuth and slope magnitude explained a greater proportion of variability in fire severity than slope magnitude alone. Prevailing wind direction, available fuel, and historical livestock grazing likely influenced the observed patterns of fire severity.