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Burn severity: Where, why, and so what?

Date: January 19, 2017
Presenter(s): Penelope Morgan
Description: Do large fire “runs” consistently result in high severity fires? What are the trends in proportion burned severely? Do climate, vegetation and topography influence burn severity in the same way that they affect area burned? How do severe fire disturbances influence vegetation response? I draw on recent and ongoing work to address these questions using burn severity inferred from satellite imagery and historical aerial photographs, and with field data on vegetation response. Compared to area burned, burn severity is more influenced by local topography, vegetation and fuels, whether analyzed for four ecoregions in western US, or for 2697 daily areas burned on 42 fires in forests of the US northern Rockies. Proportion burned severely was weakly correlated with area burned in a day. Median proportion burned with high severity was 13% and 49% for daily areas burned less than and more than 108 ha, respectively. Long temporal records are useful. The proportion of area burned with high severity did not increase over the last 133 years in the Selway-Bitterroot Wilderness where more area burned severely early and late compared to the middle 1900s. High severity burns in the early 1900’s limited the extent and severity of subsequent fires with implications for management of future large fires. Tree seedling density establishing post fire was nil for the 25% of area burned in 21 large fires that was more than 95 m from surviving trees for warm-dry forests in the US northern Rockies. There is a legacy of past disturbances, though the effects on subsequent tree seedling density of severe fire are more pronounced than severe bark beetle or both. As we learn more about the spatial variability in burn severity, we are understanding broad implications for how fire affects vegetation, and implications for both current and future fire management that hinge on the relative importance of climate and fuels for future high severity fires. 
Topic(s): Fire Effects, Ecological - First Order, Fire Intensity / Burn Severity, Fire Regime
Ecosystem(s): None
Type: Webinar
NRFSN number: 15098
Record updated: May 24, 2018