Natascha Kljun

While many studies have examined carbon dynamics of boreal ecosystems following wildfire, research on forest-atmosphere carbon fluxes during widespread smoke events from adjacent active wildfires is limited. We examined eddy covariance carbon exchange adjacent to the May 2011 Utikuma Complex wildfire in central Alberta, Canada. Over a one-week period while the wildfire was burning <10 km from the flux footprint of the tower, net ecosystem CO₂ exchange decreased to almost zero, likely due to smoke-related reductions in photosynthetically active radiation greatly diminishing photosynthesis. The smoke event caused a direct reduction in forest CO₂ sequestration by 0.7 Tg CO₂ during the fire period. As the smoke affected area was 120 times greater than the burnt area itself, this additional carbon reduction was equivalent to ~30% of gross carbon emissions from the fire. We argue that smoke-related inhibition of photosynthesis via reduced light availability should be considered when investigating the net impacts of high-intensity boreal wildfires on the net radiative forcing and global carbon balance.