The Strength of Fuel Self‐Regulation in Alaska's Wildfire Regimes

Abstract

Fuel depletion following wildfires in the North American boreal forest can temporarily reduce the probability of a subsequent fire. Landscape‐wide shifts to younger, less flammable forests may act as an important negative feedback to a warming‐driven increase in biomass burning, but only if regenerating‐fuel limitations remain strong during severe fire weather. We assessed the climate sensitivity of regenerating‐fuel limitations within Alaska's historical fire regime by analyzing 568 examples where fires either spread into or stopped at the edge of a previously mapped burn between 1984 and 2020. We classified every 30‐m pixel located along the contact perimeters of interacting fires as either reburn or limited incursion and then used logistic regression to assess the number of years since last fire (YSLF), contact perimeter length, and fire weather indices as predictor variables. Over the course of the first 30 YSLF, contact perimeters became ∼2.5x less likely to limit fire spread, and up to 2x less likely under extreme fire weather conditions. Rates of reburning by area were one to three orders of magnitude lower than rates of burning in >35‐year‐old fuels. Using these observations to parameterize a statistical fire model, we estimate that the rates of historical burning would have been ∼4.9x greater without the negative feedback created by fuel limitations. We conclude that fuel limitation has been an important, self‐regulating aspect of Alaska's wildfire regimes, and while it will weaken as climate change accelerates, this negative feedback will continue to significantly limit fire spread.