Summary
Fire severity, the impact of the fire on an ecosystem, is among the most challenging dimensions of fire to quantify empirically. Forest Service researchers measured fire severity of the Pagami Creek wildfire that burned nearly 100,000 acres in the Boundary Waters Canoe Area Wilderness in northern Minnesota using multiple standardized indices. They compared these indices with ecosystem processes including loss of carbon (C), nitrogen (N), and mercury (Hg) from soils and forest floor and subsequent aspen regeneration. Emissions from the wildfire were estimated as the annual equivalent C emissions from 50,000 sport utility vehicles emissions, the N required to fertilize 163,000 acres of corn, and approximately 9 percent of the 2010 Hg emissions for the state Minnesota. These losses were primarily from the forest floor and strongly related to soil post-fire severity indices measured at very fine spatial scales (less than 1 meter). Aspen regeneration was unrelated to the normalized burn ratio, but strongly related to prefire aspen abundance, each measured using satellite-based remote sensing. The research demonstrates (1) forest fires have large consequences for ecosystem processes such as biogeochemical cycling and forest vegetation dynamics; and (2) the importance of both scalable and repeatable measures of fire severity related to these crucial ecosystem processes.
