Canadian Forest Service Publications

Variability and drivers of burn severity in the northwestern Canadian boreal forest. 2018. Whitman, E.; Parisien, M.-A.; Thompson, D.K.; Hall, R.J.; Skakun, R.S.; Flannigan, M.D. Ecosphere 9(2):e02128.

Year: 2018

Issued by: Northern Forestry Centre

Catalog ID: 39254

Language: English

Availability: PDF (download)

Available from the Journal's Web site.
DOI: 10.1002/ecs2.2128

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Burn severity (ecological impacts of fire on vegetation and soils) influences post‐fire stand structure and species composition. The spatial pattern of burn severity may compound the ecological impacts of fire through distances to seed sources and availability of bud banks and seedbeds. Land managers require spatial burn severity data to manage post‐fire risks, ecosystem recovery, and assess the outcomes of fires. This research seeks to characterize and explain variability in burn severity in the northwestern boreal forest. We assessed burn severity one year post‐fire in six large wildfires that burned in 2014. We measured burn severity using the Composite Burn Index, surface Burn Severity Index, Canopy Fire Severity Index, and percent overstory mortality, describing a range of surface and overstory fire effects. Burn severity was variable, ranging from unburned residuals to complete overstory mortality and intense combustion. We related field measurements to remotely sensed multispectral burn severity metrics of the differenced Normalized Burn Ratio (dNBR), the Relativized dNBR, and the Relativized Burn Ratio. Diagnostic models of burn severity using relativized metrics had lower errors and better (though not significantly so) fits to the field data. Spatial patterns of burn severity were consistent with those observed in other large fires in North America. Stand‐replacing patches were large, aggregated, and covered the largest proportion of the landscape. These patterns were not consistent across the four mapped burn severity field metrics, suggesting such metrics may be viewed as related, but complementary, as they depict different aspects of severity. Prognostic models indicated burn severity was explained by pre‐fire stand structure and composition, topoedaphic context, and fire weather at time of burning. Wetlands burned less severely than uplands, and open stands with high basal areas experienced lower burn severity in upland vegetation communities. This research offers an enhanced understanding of the relationship between ground observations and remotely sensed severity metrics, in conjunction with stand‐level drivers of burn severity. The diverse fuel complexes and extreme fire weather during the 2014 fire season produced the complex patterns and broad range of burn severity observed.

Plain Language Summary

Land managers in the boreal forest region need to know how wildfires affect vegetation and soils so that they can address the immediate hazards resulting from fires and manage the long-term recovery of ecosystems that have been burned. The authors wanted to find out if data gathered from satellite images through remote sensing technology provide a good representation of the severity of the effects of fires on vegetation and soils (called burn severity) in northern Canadian boreal forests. To do this, they compared remote sensing data with information they collected in the field one year after six very large wildfires that burned in 2014 in the Northwest Territories and northeastern Alberta. At their field sites, they gathered information on various measures of burn severity, such as the extent of combustion (burning) in tree crowns and on the forest floor and how many trees had died. They found that the remotely sensed data were meaningfully related to their field measurements of burn severity, and that pre-fire forest structure and composition predicted burn severity. The results of this study suggest that land managers can use remote sensing data to ascertain the ecological effects of wildfires in northern forests, which can be difficult or expensive to visit.