In 2013, the Rim Fire burned a large area across the Stanislaus National Forest and Yosemite National Park during the second year of the most extreme drought in the historical record. Like other large fires in Sierra Nevada mixed-conifer forests, broad areas of the Rim Fire burned at higher severity than would have occurred historically.
PNW scientist Bob McGaughey helped conduct a study of the Rim Fire, exploring the different factors and conditions that influence burn severity patterns.
The study team was able to use pre-existing remote sensing data from LiDAR measurements taken in 2010 within the Rim Fire perimeter. Typically collected by an airplane or helicopter, LiDAR uses pulsed laser beams to generate precise, three-dimensional information about the surface of the Earth. In forested landscapes, LiDAR can reveal important forest structure information like tree canopy heights, stand volume, and aboveground biomass. The availability of prefire airborne LiDAR data over a portion of the fire allowed the study team to examine whether these high-fidelity forest structure measurements would improve their ability to explain burn severity patterns.
Differences in patterns of burn severity for previous fires and the Rim Fire were best explained using predictors for water balance, slope position, and local topography. For the Rim Fire, incorporating previous fire history and fire weather metrics modestly improved results.
“We were surprised to find that prefire LiDAR measurements of forest structure did not improve our ability to explain Rim Fire burn severity patterns,” said study authors. This could be because the overstory forest structures picked up by LiDAR don’t necessarily represent surface fuels accurately.
Study results suggested that local conditions like water availability and topography can help predict likely burn severity patterns under moderate climate and fire weather conditions. This information provides managers with general guidance for prioritizing fuel treatments and identifying where fire is less likely to burn with higher severities.