Detecting regional differences in within-wildfire burn patterns in western boreal Canada

Abstract

Under the auspices of ecosystem-based management (EBM), using historical range of variation (HRV) knowledge to help guide forest management decision-making is becoming commonplace. In support of this evolution, we hypothesized that historical fire-scale wildfire burn patterns in western boreal Canada could be differentiated by major ecological zones. We tested 10 fine-scale burn pattern metrics for 129 natural wildfires across more than 100 million ha of western boreal Canada against existing Canadian and provincial ecological classification schemes. The results showed some evidence of two historic disturbance regimes. Fires in the Foothills and Rocky Mountain ecoregions tended to have more disturbed patches, a smaller dominant disturbed patch, and less area in partially disturbed island remnants relative to fires in the Boreal Forest and Boreal Shield. However, several key metrics such as event shape and total remnant area were zone-invariant. Fire regime parameters such as fire size and frequency may not be linked to more detailed fire behaviour parameters such as remnant patterns. The moderate, yet highly variable levels of remnant pattern variation we found across the study area represents a natural, and potentially universal source of structural and compositional diversity for the boreal that may be critical to its sustainability.

Vegetation Mortality within Natural Wildfire Events in the Western Canadian Boreal Forest: What Burns and Why?

“…At the event scale, overall vegetation mortality was moderately influenced by Ecoregion reflecting the broad ecological patterns first identified by [12], and found by others [15,16]. Fires within both the Foothills and Rocky Mountains had lower proportions of remnants in partial mortality classes and higher proportions of high mortality than other Ecoregions.…”

“…Fire weather conditions may be critical for the formation of moderate levels of vegetation mortality, while fuel-type and topography differences may over-ride fire weather and play a more dominant role for determining areas that are either unburned or burned with high mortality. The higher proportion of fires that burned with high levels of island remnants found in the Foothills relative to the Boreal Plains reported by Andison and McCleary [12] support this concept. In any case, given the prevalence of partial mortality noted recently in boreal wildfires, this would seem an obvious target for future research.…”

“…Other data collected and used in the analyses included Ecoregion, as defined by a blending of the Alberta and Canadian Ecoregions (see [12] for details). The event area was calculated (including unburned islands) and assigned to each pixel within each respective fire event.…”

“…For example, Ecoregion was previously associated with the proportion of vegetation mortality within fire events [12,26], certain fuel types and percent cover variables have been linked with vegetation mortality and burn severity [28,46,56], topography has been related to burn severity [15,50], and fire weather variables exhibited weak relationships to burn severity [21]. While this study confirms many of these previously found relationships, it reveals a new level of complexity in terms of the processes involved in the formation of remnants.…”

“…The scale of the aerial photographs was either (a) better than 1:20,000 or (b) large format plates greater than 1:31,860 of sufficient quality to resolve individual trees (see [12,29] for details). In the Softcopy environment, photo-pairs were used to define the outer boundaries of each fire (i.e., the "shell"), and map all remnants using six mortality classes: class 0 = no mortality, 0%; class 1 = 1% to 25%; class 2 = 26% to 50%; class 3 = 51% to 75%; class 4 = 76% to 94%; and class 5 = ≥95%.…”