Topography, Climate and Fire History Regulate Wildfire Activity in the Alaskan Tundra

Although the link between climate change and tundra fire activity is well-studied, we lack an understanding of how fire, vegetation, and topography interact to either amplify or dampen climatic effects on these tundra fires at Pan-Arctic scale. This study investigated the relative influence of fire history, climate, topography and vegetation on fire occurrence and size in Alaskan tundra (1981-2019) and the potential for self-reinforcing/limiting fire behavior. Regime shift analysis identified a step increase in fire frequency after 2010 with increased average annual area burned (+96%) and area reburned (+61%) over the 2010-2019 period, consistent with climatic thresholds in fire activity being crossed. Correlation analysis shows variation in fire frequency was positively and significantly related to mean summer temperatures. The competing roles of fire history and bio-climate were investigated via random forest models using (a) environmental conditions and (b) environmental conditions and fire history. Fire occurrence was primarily driven by topographic complexity and elevation, suggesting that areas at 50-200 m elevation with gently rolling terrain such as the Arctic Foothills of the Brooks Range or the Kotzebue Lowlands in northern Alaska will likely become hotspots of fire activity. In contrast, fire size was affected mainly by fire history and winter-spring climate, which demonstrates the importance of both fuel limitations and self-reinforcing (e.g., rapid fuel regrowth following smaller-sized fires) fire-vegetation interactions in regulating tundra fire activity. Future modeling studies need more nuanced representations of fire-terrain and fire-vegetation interactions to accurately project how tundra ecosystems may respond to climatic warming.