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

Abstract

Abstract:Wildfires are a common disturbance event in the Canadian boreal forest. Within event boundaries, the level of vegetation mortality varies greatly. Understanding where surviving vegetation occurs within fire events and how this relates to pre-fire vegetation, topography, and fire weather can inform forest management decisions. We used pre-fire forest inventory data, digital elevation maps, and records of fire weather for 37 naturally-occurring wildfires (1961 to 1982; 30 to 5500 ha) covering a wide range of conditions in the western Canadian boreal forest to investigate these relationships using multinomial logistic models. Overall, vegetation mortality related to a combination of factors representing different spatial scales. Lower vegetation mortality occurred where there was lower fuel continuity and when fires occurred under non-drought conditions. Higher classification accuracy occurred for class extremes of no mortality (i.e., unburned areas within the burn event) and high mortality; partial vegetation mortality classes were harder to distinguish. This research contributes to the knowledge required for natural pattern emulation strategies, and developing responses to climate change.

Variability and drivers of burn severity in the northwestern Canadian boreal forest

“…); however, this proportion was smaller than the 64% observed by Ferster et al. () in the same boreal plains ecoregion. Although area burned severely increases with increasing fire size, it has also been suggested that larger fires tend to have larger residual stands and a higher proportion of unchanged patches in the boreal forest (Eberhart and Woodard , Madoui et al.…”

“…The fires studied here are of a substantial size, with only six fires burning more than 1,400,000 ha in a single year, an area equivalent to that burned by 295 fires over 26 yr in the montane study area examined by Harvey et al (2016b), and over four times the area burned by 125 fires over 24 yr in a study of the northern Cascade Range (Cansler and McKenzie 2014). The proportion experiencing complete mortality was much higher than the average proportions of stand-replacing fire observed in the western United States (Cansler and McKenzie 2014, Harvey et al 2016b; however, this proportion was smaller than the 64% observed by Ferster et al (2016) in the same boreal plains ecoregion. Although area burned severely increases with increasing fire size, it has also been suggested that larger fires tend to have larger residual stands and a higher proportion of unchanged patches in the boreal forest (Eberhart andWoodard 1987, Madoui et al 2010).…”

“…Although pre-fire stand structure, composition, and topoedaphic context have a role in determining burn severity in this region , Ferster et al 2016, there is still substantial variability in observed severity. A typical median level of burn severity is apparent within individual vegetation communities, but measured burn severity was quite variable, with some communities capable of burning at particularly broad ranges of severity.…”

“…Analyses of the landscape pattern of stand-replacing fire in such ecosystems show that large fires, like those characteristic of the boreal forest fire regime, tend to incorporate moderately high proportions burned severely (~25%), and that stand-replacing patches are often large, simple in form with substantial core areas, and aggregated, with some variability driven by local climate and vegetation McKenzie 2014, Harvey et al 2016b). It is therefore possible to characterize the landscape patterns of diverse overstory and understory burn severity metrics in the northwestern boreal forest, relative to documented patterns of stand-replacing fire in this (Kafka et al 2001, Ferster et al 2016) and other ecosystems (Cansler and McKenzie 2014, Harvey et al 2016b). In the boreal forest, however, many tree species have adaptations that provide in situ budding rhizomes or seed sources following fire, regardless of tree mortality (Greene et al 1999), suggesting that ecological characterizations of landscape patterns of burn severity in this region should address other fire effects, in addition to overstory mortality (Bergeron et al 2014).…”

Revisiting Wildland Fire Fuel Quantification Methods: The Challenge of Understanding a Dynamic, Biotic Entity

“…While this approach is unique to Australia, such patterns of recovery are not (e.g., [99,100]). Furthermore, with variation in post fire conditions [27] or fire severity [101,102] having the potential to influence vegetation recovery, using time since fire as the sole moderator of fuel properties may not necessarily deliver outcomes that meet manager's expectations. Additionally, fire is only one of many potential disturbances that can impact fuels-it may also be important to recognise other disturbances such as timber harvesting or drought.…”