OOS 36-3 - 100 years of fire suppression has eroded landscape-scale pyrodiversity in northern British Columbia's sub-boreal and montane forests

Background/Question/Methods
Forest ecosystems across western North America are increasingly experiencing large and severe wildfire disturbances. In 2017, 2018, and 2021 approximately 3.5 million hectares of forests in British Columbia (BC), Canada were impacted by severe wildfires, intensifying the need to understand current wildfire events and their departure from historic fire regimes. Although the best available science supports the use of controlled fire as a primary tool to mitigate wildfire risk, knowing where, when, and how to apply fire across the broader land base is not straightforward. Although much of BC’s pyrodiversity has been shaped by both natural and cultural fire histories, several barriers exist in applying controlled (both prescribed and cultural fire), engaging in modified wildfire response plans, and revitalizing Indigenous-led fire stewardship. The objectives of our study were to determine historic fire regime variability in Tweedsmuir Provincial Park using old growth whitebark pine trees, several exceeding 800 years in age. This is the first fire history completed in the park and we reconstructed the timing, severity, and spatial extent of historic fire events using the presence of fire-scarred trees.

Results/Conclusions
Our fire history record extended 750 years, with 25 fire events recorded over a 250 year period (1711-1957). Our results indicate two key findings. First, all study areas recorded low-severity fires, occurring every 5-10 years. Second, our results highlight the important role of cultural burning which creates complex temporal and spatial patterns that are critical to forest and species resilience. Previous estimates of fire regimes in our study area were for high severity, stand-replacing fires occurring every 100-300 years. Our study provides important historical context for contemporary wildfire events which are likely artefacts of over a century of natural and cultural fire exclusion. Reducing economic, social, and cultural barriers is critical to engaging in successful wildfire mitigation strategies, applying controlled fire, and supporting a more informed and inclusive understanding of the future of fire on the land base. Given the vulnerability of Indigenous peoples in BC to the impacts of wildfire, it is more important than ever to have Indigenous experiences and voices leading fire conservation strategies that are both effective and socially just.