Print PageFor decades, wildfire studies have utilized fire occurrence as the primary data source for investigating the causes and effects of wildfire on the landscape. Fire occurrence data fall primarily into two categories: ignition points and perimeter polygons which are used to calculate a ‘burned area’ for a fire. The challenge to understanding ecological and climatological relations with fire occurrence is that fires do not generally burn homogeneously across the landscape, nor do they generally consume 100 percent of the area bound by the perimeter. This research characterizes unburned areas within the fire footprint, which provide an ecological refugia and seed source for post-fire regeneration. We utilized differenced Normalized Burn Ratio (dNBR) data from the Monitoring Trends in Burn Severity project to look at patterns of unburned area in three national parks across the western US (Glacier, Yosemite, and Yukon-Charley Rivers). In this paper, we characterize unburned area within fire perimeters by fire size and severity, characterize distance to an unburned area across the burned portion of the fire, and investigate patch dynamics of unburned patches within the fire perimeter.
Results/Conclusions
From 1984 through 2009, the total area within the fire perimeters that was classified as unburned from dNBR was 37 percent for Yosemite, 17 percent for Glacier, and 14 percent for Yukon-Charley Rivers, with the greatest range of proportion unburned in Yosemite, and the lowest range in Yukon-Charley. Unburned proportion significantly decreased with increasing fire size and severity across all three parks. Unburned patch size increased with size of fire perimeter, but patches decreased in density. There were no temporal trends in unburned area found. These results raise questions about the validity of relationships found between external forcing agents, such as climate, and ‘burned area’ values derived solely from polygon fire perimeters.
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