Recent research in the European boreal forest has revealed that areas affected by wildfires continue to emit carbon dioxide (CO2) for years after the fires subside, posing a significant threat to this vital carbon sink.
The boreal forest, a vast green belt stretching from North America to Siberia, plays a crucial role in carbon sequestration.
Over millennia, it has stored approximately 1 trillion tons of CO2 in its trees and soil.
However, climate change is predicted to make wildfires more frequent and severe in these northern latitudes.
While wildfires are known to release large amounts of CO2 during combustion, this new study has found that the post-fire emissions exceed the initial emissions released during the fire.
The research, titled Wildfire impacts on the carbon budget of a managed Nordic boreal forest, was conducted by scientists from Lund University in Sweden, Swansea University in the UK, and the University of Oviedo in Spain.
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In 2018, extreme heat and dry conditions led to an unprecedented number of wildfires in Nordic countries, particularly in Sweden, where the burned area was ten times larger than average.
Researchers focused on the most extensive fire near Ljusdal, on the Baltic Sea coast of Sweden, continuously measuring CO2 exchange between the land and atmosphere and monitoring soil and vegetation regrowth for four years post-fire.
The study compared areas where trees were killed, areas where trees survived, and areas subjected to different post-fire management strategies, including nature reserves with standing charred trees and salvage logging with replanting.
Findings showed that heavily degraded sites, such as those with salvage logging, emitted 650g of carbon per square meter (10.8 sq ft) annually for four years, more than doubling the fire’s initial emissions.
In contrast, an unburned forest would have removed 1,200g of carbon per square meter in the same period.
Model simulations predicted it would take over 40 years for new forests to reabsorb the CO2 emitted by the 2018 fire.
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This prolonged emission period highlights the importance of post-fire management, Natascha Kljun and Julia Kelly, two of the authors of the study, explained in an article, published in The Conversation earlier this week.
Practices like salvage logging and soil plowing can hinder vegetation recovery, whereas leaving surviving trees standing, even if growth is slower, aids in continuous CO2 capture.
The study underscores the need for climate models to account for long-term CO2 emissions from post-fire landscapes, not just the immediate fire emissions, Kljun and Kelly concluded.
