RAPID: Increasing fire severity and the loss of legacy carbon from boreal ecosystems

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One of the most rapid ways climate warming could alter the carbon balance of high northern latitude conifer forests and peatlands is through more intense wildfires. Most of the carbon that can burn occurs in thick soil layers often hundreds to thousands of years old that are a legacy of past wildfires, and combustion of these layers accounts for the largest source of carbon released during fires. In the summer of 2014, wildfires burned 3.4 million hectares of forested lands of the Northwest Territories (NWT), Canada, eight times greater than the average annual area burned, and twice as much area as burned in United States wildfires that year. This project will study the impacts of these fires on the combustion of legacy carbon. Researchers will also join a rapid-response Canadian team to greatly facilitate access via floatplane and helicopter, and to gain access to geospatial data. Results will be shared with land and fire managers in collaboration with the NWT Division of Forestry and the Alaska Fire Science Symposium and through a winter webinar. The project will also provide new international research experience for a PI, postdoctoral researcher and undergraduate student.The objective of this project is to develop a mechanistic understanding of fire characteristics that control legacy carbon loss in these ecosystems. More intense fires result in deeper burning and ultimately determine whether more intense fires will accelerate climate warming via the carbon cycle, as has been proposed. They also could rapidly shift ecosystems across a threshold from net accumulation of carbon from the atmosphere over multiple fire cycles to net loss. High fire intensity across large and varied landscapes and multiple, spatially independent fire scars will enable a study design with replicate natural fire severity gradients across key landscape positions. A novel application of radiocarbon dating will be combined with widely used and scalable metrics of organic matter combustion to quantify the magnitude of legacy carbon loss on a site-specific basis. Permanent plots will be established for long-term monitoring of permafrost and vegetation, key controls over the carbon cycle in this biome. An early campaign will enable the best estimates of site-specific carbon emissions, legacy losses, initial subsidence of permafrost and ensuing changes in site drainage, and dispersal of semi-serotinous seeds. This research will contribute to emerging ecosystem theory on cross-time scale linkages and interactions and the role these may play in the resilience or vulnerability of ecosystem processes to shifting disturbance regimes.