Historical fire regimes in whitebark pine ecosystems of west-central British Columbia

Abstract

Forest ecosystems across western North America are experiencing increasingly large and severe wildfire disturbances. From 2012 to 2024, approximately 600,000 ha of forest in Tweedsmuir Provincial Park, British Columbia's largest protected area, were impacted by wildfires. These wildfires burned primarily through lower elevation subboreal forests, but high-severity fire also impacted subalpine and treeline ecosystems across the mountainous provincial park. Whitebark pine is a long-lived and endangered high-elevation tree species experiencing extensive mortality throughout western North America from an invasive pathogen and recent large-scale outbreaks of mountain pine beetle. To understand the impacts of changing fire regimes on subboreal and subalpine whitebark pine ecosystems, we reconstructed the first fire history in North Tweedsmuir Provincial Park. Eleven study sites containing whitebark pine were sampled along lakeshores, islands, knolls, and ridgelines. Our fire history record indicated two key findings. First, fire-scarred trees provided evidence of low-severity fire at all 11 study sites. Our dendrochronological record covered 830 years (1190–2020) and included 127 fire scars during a 580-year period (1377–1957), with a composite mean fire interval of 8 years in the period 1580–1957 recorded across the study area. Second, our results highlight centuries of Indigenous fire stewardship that, combined with lightning, comprised the historical fire regime. Prior to 20th century fire suppression policies, the fire regime was characterized by shorter fire intervals than the contemporary period, effectively reducing available fuels, and creating a mosaic of burned and unburned forests across the landscape. Our research findings highlight the need for proactive and dynamic wildfire management that supports multiple cultural and ecological values across protected areas.