Remote Sensing of Wildfire Burn Severity on Managed and Thinned Forest Areas of the Pacific States

Although wildfires have shaped the ecology of western U. S. ecosystems for millennia, over the last three decades fires have increased in size, severity, and frequency in most western forests of North America. This study aims to enhance our understanding of wildfire impacts by leveraging advanced remote sensing technologies. About 14 million acres (40%) of California's forested land area are owned and managed by families and native tribes, whereas 5 million acres (14%) are managed by industrial timber companies. To reduce wildfire risk, the state of California has set a new goal of logging and thinning 1 million forested acres per year. Given this background, and the uncertainties about the effects of managed tree thinning and timber harvest on fire burn severity, the following research question was addressed in this project "Does the thinning and harvest of large trees in managed timberlands increase the rate of spread and the severity of wildfire burning by potentially opening up the forest to increased surface heating heat and wind velocities?" The analysis was conducted in QGIS and Google Earth Engine using Landsat and NAIP aerial imagery. Results showed that the highest levels of burn severity since 2013 in managed forest areas of the Pacific states (CA, OR, and WA) occurred in landscapes where extremely high levels of pre-fire live forest biomass remained in large patches around equally large thinned and logged forest areas. We hypothesize that this type of mixed-age management plan creates a potentially explosive fuel loading status in a forest, whereby wildfire can be readily carried by high winds over and around patches of low biomass stands that have been recently thinned and logged.