Large Carbon Losses From Burned Permafrost Peatlands During Post-Fire Succession

Abstract The carbon (C) storage of boreal peatlands is threatened by an intensifying wildfire regime.
Between 2019 and 2023 we used eddy covariance and surface closed chambers to monitor two permafrost
peatlands in boreal western Canada that burned in 2019 and 2007. Deeper thaw, warmer soils, and slow
vegetation recovery caused the 2019 Burn to be a net carbon dioxide (CO2) source (+130 g C m 2 yr 1) for four
years post‐fire, despite reduced soil respiration. The 2007 Burn was a sink ( 11 g C m 2 yr 1) 13–15 years post‐
fire, similar to undisturbed peatlands. We estimate that wildfire caused a loss (∼2.9 kg C m 2) from permafrost
peatlands, with ∼1.7 kg C m 2 due to combustion and ∼1.2 kg C m 2 due to net CO2 losses during post‐fire
succession. This highlights the importance of the post‐fire CO2 losses and emphasizes the vulnerability of
permafrost peatland soil C to fire.
Plain Language Summary Boreal peatlands across northwestern Canada with permafrost have
accumulated vast amounts of carbon (C) over millennia despite regularly burning in natural wildfires. Ongoing
climate change increases fire frequency and intensifies fire severity, possibly transforming the ecosystems of
this vast region into long‐term future C sources. Losses of C occur during wildfire but also in the years post‐fire
due to reduced uptake of the greenhouse gas carbon dioxide (CO2) by vegetation and through decomposition of
exposed drier peat on the surface. We report measurements of net CO2 release from a recently (2019) burned
permafrost peatland in the first four years after the fire and compare them to concurrent measurements at a
nearby burned peat plateau recovering from a 2007 wildfire. Our results suggest large net CO2 losses in the first
years after fire but a return to net CO2 gains in burned peatland complexes 15 years after fire. However, active
layer deepening post‐fire and warmer soil temperatures at depth can cause the release of deep, old C. Future
work must account for both the significant magnitude and the origin of post‐fire CO2 emissions, as previously
frozen, old C is being reintroduced to the atmospheric C cycle, fueling further global warming.