The Legacy Carbon Collaborative: A network to assess the impacts of wildfires on the long-term carbon storage of boreal and tundra ecosystems

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Xanthe J. Walker, Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ and Michelle Mack, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ

Background/Question/Methods
Intensification of wildfire disturbance is one of the most rapid pathways through which climate warming could alter the structure and function of high-latitude ecosystems. More severe and frequent wildfires can shift these ecosystems across a carbon (C) cycle threshold: from a net C sink to a net C source to the atmosphere. This shift can occur when organic soil C that escaped burning in previous fires or that has accumulated over centuries, termed ‘legacy carbon’, combusts. Understanding this switch is critical for assessing the impacts of changing fire regimes on the future net ecosystem C balance (NECB) of high-latitude regions. As boreal and tundra ecosystems store 40% of terrestrial C, changes in their NECB will impact the global C cycle and climate.
Here, we investigate the impacts of intensifying wildfire regimes on the long-term C storage of boreal and tundra ecosystems by determining the frequency of legacy C loss across the circumpolar region. We have assessed legacy C loss from the 2014 wildfires in the Northwest Territories (NWT) of Canada and are collaborating with 12 research groups with additional sites across North America, Europe, and Russia. Each group has agreed to collect and send soil samples from 10 recently burned boreal or tundra sites within their respective study regions. At Northern Arizona University, we have used radiocarbon dating to assess legacy C combustion and we will hold a data synthesis workshop for all collaborators.
Results/Conclusions
In the 2014 wildfires in the NWT, which burned 2.85 million ha and emitted 94.3 Tg C, we found evidence of legacy C combustion in forests that were <60 years old at the time of fire. We therefore expect that more frequent wildfires will lead to legacy C loss across the circumpolar region and that this will vary with fire severity and soil drainage, primary factors shaping C storage in high latitude ecosystems. Measuring legacy C loss across a diverse array of ecosystems will allow us to determine the frequency at which fires switch these ecosystems from a net C sink to a net C source to the atmosphere and the potential drivers of this shift. We invite anyone interested in participating in the Legacy Carbon Collaborative to contact Xanthe Walker at Northern Arizona University (email: xanthe.walker@gmail.com).