Rapidly warming temperatures in Alaska have driven increases in the frequency of short-interval fires, or reburns, which occur in intervals of 30 years or less, well outside of historic norms of 150-300 years. Continued reburning in Alaska can spark conversions in stand composition and stand structure from dense conifer-dominated communities to deciduous-dominated open parklands. Historically, deciduous landscapes are less flammable compared to coniferous counterparts, and have acted as a self-regulating negative feedback to future burning. This trait is still relied on by land and fire managers as fire breaks within expectations of future ecosystem flammability and carbon balance. However, the strength or duration of that self-regulation remains unclear, given reburn-driven changes in structure, carbon storage and composition. To explore the future characteristics of self-regulating fire feedbacks in Alaska, we evaluated potential boreal forest fire behavior in the emerging novel fuel-scape using a combination of empirical and modeling approaches. We quantified fuel composition, abundance, and fine-scale connectivity in stands in Interior Alaska after 1, 2 or 3 fires in short-intervals, and generated representative landscapes to burn using HIGRAD/FIRETEC, a physics-based combustion model. We also quantified carbon storage in aboveground and belowground pools.
Results/Conclusions
Fuel structure shifts with reburning: sites that have burned 2 or more times in short-intervals are more open, with greater abundance in fine coarse fuels and ground cover compared to once-burned or unburned stands. Carbon storage also shifts: reburned stands have less aboveground and soil carbon. We present results of fire behavior under a gradient of fuel connectivity and abundance based on real reburned landscapes. This work provides crucial insight into the mechanistic drivers of fire activity and the sensitivity of boreal fire regimes to novel fuel structures that are emerging as fire frequency increases in the north, targeted at that important question: How will fire and fire feedbacks change in the boreal as the forest continues to change in emerging climates?
