Driven by a southwest air flow, the “Jasper South Fire” advanced northwards down the Athabasca Valley from July 22-26, 2024 into the townsite. Forest biomass conditions in the valley were likely unprecedented with <2% probability for a small area, and much less for the whole valley.
Historically, fires in the middle Athabasca valley were relatively common with a frequency of <40 years on the valley bottom ranging up >80 years on upper slopes (Tande 1979, Chavardès et al. 2018). Indigenous peoples probably lit most of these burns in moderate weather conditions—constraining the area burned and the intensity/severity of the fires. Assuming an average fire cycle of 60 years, and characterizing biomass by vegetation types classified by the Banff-Jasper Ecological Land Classification (Achuff and Corns 1982) yields estimates the estimates of representative biomass conditions over time for the montane and warm/dry lower subalpine ecoregions (White 1985a).
A biomass scenario for the Athabasca Valley south of Jasper townsite with a ~60 year fire cycle prior 1775, post-contact and fire suppression from 1776 to 2024, followed by potential restoration of the long-term cycle.
Assuming relatively constant climate and an equal flammability with stand age, the scenario shows the probability that the fire intervals would be at least as long as shown. During the Indigenous period, the 1725 and 1775 fire intervals had high probabilities of occurring. Moderate fire intensities would have only partially burned the forests, with biomass averaging between 100-200 tons/ha. However, during the post-contact and fire suppression periods (~1776 to 2024) a long fire-free period occurred that would have had only very low probably of occurring in previous times (p=.02). As a result, biomass exceeded 300 tons/ha. Through decomposition, downed wood biomass declined during the 1800s before beginning to increase in the mid-1900s as lodgepole pine mortality increased, culminating with a mountain pine beetle mass attack in the late 1990s. Ground fuels, and canopy bolewood and branchwood/foliage biomass increased steadily during the period. A decreasing height to live crown foliage, and increased crown density yields higher crown fire potential. Increased common juniper cover (an explosive shrub component) also likely created conditions for intense surface fires that rapidly transition into full crown fire. This pattern of biomass accumulation change yielded the fuel complexes that set the stage for the extreme fire behavior of the 2024 burn (JFT 2025).
Next what was required was a period drought and hot weather to dry out these fuels. During the 23-day span July 1-22, 2024 the fire weather Buildup Index increased rapidly from a near-median value to an extreme level (BUI of 169), the highest value recorded for that time of year and above the 99th percentile of observations for a 62-year climatological record (JFT 2025). Under these conditions extreme fire behaviour would be expected during “30-30-30” conditions (>30 degrees C,<30% RH, >30 km per hour winds). Now, all was required was a source of ignition. On July 22 the ridge of high pressure that created the drought shifted eastwards. During the day strong SW winds blew a wave of super-heated and dried air from the deserts of Washington and Oregon across the Canadian border and pushed these up the Rocky Mountain Trench and over the mountain passes into the eastern slope watersheds. The unstable air mass created sporadic lightning, with several strikes in the Athabasca Valley. Ignitions occurred in at least 3 locations, and within minutes the nearly unstoppable Jasper South megafire erupted, and began advancing through a continuous blanket of extremely abundant fuels towards the town (JFT 2025). Within 4 days over 360 square kilometers were baked and blackened, with a massive release of carbon from the ground, downed wood and crown foliage layers, reducing biomass from >300 tons to <100 tons per hectare. Amazingly, the town itself and surrounding resorts were only about 1/3 burned due to years of FireSmart fuel reduction near buildings and fuelbreak cutting on the town’s periphery (Westhaver et al. 2007).
After the burn, the major source of remaining biomass is the dead standing trees that fall over time to the forest floor. The scenario illustrated above is based on a prediction that managers will practice active ecological and cultural restoration in the Athabasca valley over the next few decades. Prescribed burning–likely partially based on the long-term Indigenous practices– will return fire frequency to more characteristic intervals of <100 years. An initial task will be to construct fuelbreaks and reduce the massive pulse of downed wood biomass created by the 2024 burn. Over time more frequent burning will maintain generally lower biomass levels, and vegetation adapted to ongoing moderate fire intensities.
Is the Banff-Canmore Bow Valley following the Jasper 2024 scenario? Generally yes—biomass is accumulating in a similar pattern after the Indigenous depopulation of the late 1800s (Binnema and Niemi 2006). Two interacting factors have slightly reduced risk: 1) slightly younger forests due to a 20 year period of railroad-caused fires the maintained the fire regime along the Indigenous travel route through the valley, and 2) perhaps due to the overall slightly younger forests and higher elevations, mountain pine beetle is only now beginning to rapidly kill lodgepole forests. Perhaps land managers can use this window to reduce fuel abundance and continuity before the inevitable big burn.
References
Achuff, P. L., and I. G. W. Corns. 1982. “Vegetation.” In Ecological (Biophysical) Land Classification of Banff and Jasper National Parks. Volume 2: Soil and Vegetation Resources, edited by W.D. Holland and G.M. Coen,. Edmonton: Alberta Institute of PedologyVolume 2: Soil and Vegetation Resources, edited by W.D. Holland and G.M. Coen,. Edmonton: Alberta Institute of Pedology.
Binnema, Theodore, and Melanie Niemi. 2006. “‘Let the Line Be Drawn Now’: Wilderness, Conservation, and the Exclusion of Aboriginal People from Banff National Park in Canada.” Environmental History 11 (4): 724–50.
Chavardès, Raphaël D., Lori D. Daniels, Ze’ev Gedalof, and David W. Andison. 2018. “Human Influences Superseded Climate to Disrupt the 20th Century Fire Regime in Jasper National Park, Canada.” Dendrochronologia 48 (April): 10–19. https://doi.org/10.1016/j.dendro.2018.01.002.
JFT (Jasper Fire Documentation, Reconstruction, and Analysis Task Team). 2025. Jasper Wildfire Complex: Fire Behaviour Documentation, Reconstruction, and Analysis. Information Report NOR-X-433. Northern Forest Research Centre.
Tande, Gerald F. 1979. “Fire history and vegetation pattern of coniferous forests in Jasper National Park, Alberta.” Canadian Journal of Botany 57 (18): 1912–31. https://doi.org/10.1139/b79-241.
Van Wagner, C. E., M. A. Finney, and M. J. Heathcott. 2006. “Historical Fire Cycles in the Canadian Rocky Mountains.” Forest Science 52: 707–17.
White, Clifford A. 1985a. “Fire and Biomass in Banff National Park Closed Forests.” Colorado State University.
Westhaver, Alan, Brad C. Hawkes, and Richard D. Revel. 2007. “FireSmart & ForestWise: Managing Wildlife and Wildfire Risk in the Wildland/Urban Interface-a Canadian Case Study.” The Fire Environment–Innovations, Management, and Policy; Conference Proceedings. (Fort Collins, CO) Proceedings RMRS-P-46: 347–65.
White, Clifford A. 1985b. Wildland Fires in Banff National Park, 1880-1980. Occasional Paper 3. Parks Canada.