The two towers: CO2 fluxes after wildfire in managed Swedish boreal forest stands

Wildfires have been effectively suppressed in the managed boreal forests of Fennoscandia for over a century. However, recent extremely hot and dry summers have highlighted the vulnerability of these forests to increasing wildfire frequency as a result of climate change. The carbon stored by managed forests plays a key role in many national climate mitigation strategies and more data is needed to assess how forest management shapes the carbon balance of these forests, including those recovering from wildfire. We established two eddy covariance towers in the area burnt by the Ljusdal fire, which affected over 9000 ha during the extreme 2018 wildfire season in Sweden. The two towers measured CO₂ fluxes during the first four growing seasons after the fire at two Pinus sylvestris stands with contrasting fire impacts and forest management schemes. At one site, a mature stand had survived low severity fire but was then salvage-logged and reseeded (6 months after the fire), whilst the other site represented a young stand that was killed by high severity fire and replanted with Pinus sylvestris seedlings (2 years after the fire). After the fire, both sites were net CO₂ sources at the annual scale. However, the site with dead young trees and replanted seedlings showed a faster recovery towards becoming a CO₂ sink, with days of net CO₂ uptake during the peak of the growing season three years after the fire. Preliminary results suggest that similar magnitudes of carbon were emitted as CO₂ in the first 4 years after the fire compared to the carbon emitted during the fire itself, underlining the importance of monitoring forest CO₂ fluxes and the impacts of management decisions during the initial post-fire years.