The Relationship between Wildfire Dynamics and Soil Carbon in Boreal Forests of Alaska: Forest Management for Emissions Reduction in a Changing Climate

The boreal region of Alaska has vast forests spanning hundreds of thousands of square kilometers in the central portion of the state that is prone to large stand replacing summer wildfires. The region stores considerable quantities of terrestrial carbon sequestered in soil horizons down to 1 meter in depth that are strongly influenced by a combination of climate change, permafrost dynamics, vegetative composition, and fire regimes. Data and literature establish that the boreal region of Alaska (and the rest of the Arctic) has been steadily warming at a rate nearly double that of lower latitudes. This warming has resulted in larger fires defined by shorter return intervals. This altered fire regime places the vast stocks of organic soil carbon at risk to greater degrees of combustion, potentially contributing millions more tons of CO2 to the atmosphere in the Arctic region. Between 2000-2015 roughly 5% (~28,000 km2) of the over 560,000 km2 of the boreal region burned, raising CO2 levels and supporting a positive feedback loop between climate and fires; when considering that this region of Alaska is larger than the state of California (~420,000 km2) these emissions are significant. Mean summer temperatures have risen by 1.4° C over the last 100 years, resulting in shorter fire return intervals characterized by more severe and intense, longer fire seasons. This warming is driving more pronounced permafrost degradation that is altering both the extent and depth of regional permafrost layers, increasing labile carbon stocks that serve as additional fuel pools for fires. While permafrost layers are fluctuating more frequently, the warmer temperatures are supporting increased vegetation growth with expansion of the boreal forest into landscapes that were previously hostile, increasing novelty in these area’s fire regimes and subsequent emissions. As fire activity increases in the region, forest composition is being altered toward a greater dominance by deciduous rather than coniferous trees, a development that is increasing soil carbon levels as these stands mature. Human suppression policies, despite being well intentioned, are driving more frequent and severe fires due to an unnatural buildup of fuels, especially around regional population centers. Because of these findings, I recommend closing critical data gaps with further data additions, changing timber harvesting and forest management policies, and reexamining fire suppression policies