Forest ThreatNet

Volume 11, Issue 2 - March/April 2017

Western Threat Center Highlight: When Lightning Strikes, So Does Opportunity

Snags and smoke in the Pole Creek Fire

Ignited by lighting, the 2012 Pole Creek Fire in central Oregon created an opportunity for scientists to conduct a novel analysis of burn severity using remote sensing data collected before and after the fire. The study demonstrated that light detection and ranging (LiDAR) data can accurately detect change in forest canopy cover. LiDAR is a remote sensing method in which a laser instrument mounted on a small aircraft sends 100,000 pulses of light per second toward the ground. Once processed, these incredibly precise data can provide a detailed, three-dimensional description of the forest below.

The 10,800-hectare fire in the Deschutes National Forest occurred in an area with widespread mountain pine beetle damage. Over the decades, a variety of harvest treatments had occurred in two-thirds of the burn area, while the other third of the burn area fell within the Three Sisters Wilderness. LiDAR data were available from three years prior to the fire and one year after.

The researchers, including Nicole Vaillant, a fire ecologist with the Western Wildland Environmental Threat Assessment Center, used the data to analyze the influence of pine beetle outbreak and timber harvest treatments on subsequent burn severity, as determined by the change in LiDAR-estimated percentage of canopy cover.

They found that burn severity increased in areas with pine beetle damage. Timber harvest led to lower burn severity, although some harvest treatment types burned more severely than others, but not more severely than untreated sites. These findings demonstrate quantitatively that pre-fire agents of forest change are important drivers of subsequent fire effects on canopy cover.

The researchers also demonstrated that certain LiDAR data on vegetation reflectance, known as spectral indices, accurately detected change in forest canopy cover, but were primarily limited to detecting fire-induced changes in the top most canopy surface. This finding is significant given the current use of reflectance data to evaluate post-fire habitat, secondary fire effects such as flooding and erosion, comprehensive burn severity ratings, and carbon emissions.

Pictured: Snags and smoke in the Three Sisters Wilderness during the 2012 Pole Creek Fire. Photo by Todd Pease, courtesy of Inciweb.

McCarley, T. Ryan; Kolden, Crystal A.; Vaillant, Nicole M.; Hudak, Andrew T.; Smith, Alistair M. S.; Kreitler, Jason. 2017. Landscape-scale quantification of fire-induced change in canopy cover following mountain pine beetle outbreak and timber harvest. Forest Ecology and Management. 391: 164-175.

McCarley, T. Ryan; Kolden, Crystal A.; Vaillant, Nicole M.; Hudak, Andrew T.; Smith, Alistair M. S.; Wing, Brian M.; Kellogg, Bryce S.; Kreitler, Jason. 2017. Multi-temporal LiDAR and Landsat quantification of fire-induced changes to forest structure. Remote Sensing of Environment. 191: 419-432.

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