| Summary: | Boreal forests play an important role in the global carbon cycle, and wildfire is a key control of boreal carbon dynamics. Rapid high latitude climate change will likely alter boreal fire regimes, potentially disrupting the historical role of the biome as a major sink for anthropogenic carbon emissions. However, the brevity of observational fire records limits understanding of the trajectory and implications of such change. I addressed this limitation by reconstructing 10,000 years of paleoenvironmental history in the Yukon Flats of interior Alaska, incorporating the paleorecord into ecosystem model experiments, and applying insights from these approaches to the development of a statistical model for predicting fire regime change. Results reveal that recent burning is unprecedented in the last 10,000 years. Fire frequency fluctuations were the dominant control on carbon dynamics of the past millennium, and the increase in fire activity over the past several decades has caused large regional carbon losses. Fuel limitation due to fire-vegetation feedback dampened fire regime responses to centennial climate variability in the past, and a statistical model based on recent fire observations predicts that this mechanism will strongly attenuate future increases in fire activity. However, the exceptional magnitude of anthropogenic climate change will cause a pronounced increase in the rate of boreal forest burning in spite of vegetation feedback. As a result, dramatic shifts in ecosystem composition are likely across boreal Alaska, and the region will serve as a persistent source of atmospheric carbon throughout the 21st century.
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