Climate-induced fire regime amplification in Alberta, Canada

Abstract

Acting as a top-down control on fire activity, climate strongly affects wildfire in North American ecosystems through fuel moisture and ignitions. Departures from historical fire regimes due to climate change have significant implications for the structure and composition of boreal forests, as well as fire management and operations. In this research, we characterize the relationship between trends in climate and fire regime characteristics, for a study area predominantly in Alberta, Canada. We examined trends of fire and climate in northwestern boreal forests using time series analysis of downscaled historical annual climate, fire history (1970 – 2019), and fire severity (the impacts of wildfire on plants and organic biomass; 1985 – 2018). We represented fire severity using the relativized burn ratio (RBR) calculated from multispectral Landsat imagery. The climate of the study area has significantly warmed and dried over the past 50 years. Over the same period the annual number of large wildfires, area burned, and fire sizes in the study area significantly increased. Furthermore, the likelihood, area, and number of extreme short-interval reburns (≤ 15 years between fires; 1985 – 2019) also significantly increased. During the study period, the portion of forested unburned islands within fire perimeters significantly declined, and fire severity (RBR) increased in open conifer and mixedwood forests. These fire regime changes are significantly correlated with annual climate variability, and a path analysis supports the hypothesis that annual climate patterns have led to fire regime shifts. The increasing fire activity in this region has implications for forest ecology and habitat availability, as the disruption of the fire regime is likely to alter forest recovery. Managers may face increasing challenges to fire suppression if the observed trends of increasing hotter and drier annual climate in the study area persist, driving extreme fire activity.

Spatial interactions among short‐interval fires reshape forest landscapes

“…In western North America, trends of increasing homogeneity towards larger and simpler‐shaped patches of stand‐replacing fire have emerged in the Rocky Mountains (Harvey et al, 2016b), south‐west (Miller et al, 2009; Stevens et al, 2017) and north‐west (Cansler & McKenzie, 2014; Reilly et al, 2017). Similar trends of increasing fire extent and severity have been documented in other regions world‐wide (Collins, Bradstock, et al, 2021; Nolan et al, 2020; Pausas & Fernández‐Muñoz, 2012; Whitman et al, 2022). The proportion, mean patch size and patch shape complexity of high‐severity fire characterize important aspects of post‐fire landscapes that underpin mechanisms of resilience, such as the extent and diversity of remnant forest patches (Meddens et al, 2018) and the distance to seed sources required for post‐fire forest recovery (Gill et al, 2022).…”

Disturbances in North American boreal forest and Arctic tundra: impacts, interactions, and responses

“…As in many other ecosystems, fires have dramatic and extensive impacts on vegetation cover and carbon dynamics in the ABZ, and exceptional warming in this region is intensifying fire regimes (Soja et al 2007, Kasischke et al 2010, Veraverbeke et al 2017, McCarty et al 2021, Whitman et al 2022. However, the unique characteristics of ABZ ecosystems result in additional types of disturbances that lack analogs in tropical and temperate ecosystems.…”

Converging and diverging burn rates in North American boreal forests from the Little Ice Age to the present

“…Similar findings were also reported in Alaska, with the 2000s showing greater burned areas than the preceding six decades (Kasischke et al 2010). These increases in burned areas were attributed to significantly warmer and drier climate over the later half of the 20th and early 21st centuries in western Canada (Whitman et al 2022) and Alaska (Kelly et al 2013). As warmer and possibly drier climate may well override the capacity to suppress fire (Flannigan et al 2009) it remains uncertain if the observed decrease of burn rates in eastern Canadian boreal forests will continue in the future.…”