WEDNESDAY, APRIL 7TH, 2021
Carbon has been stored in the organic layers of boreal-forest soils for hundreds of years. An analysis reveals that this carbon might be released into the atmosphere as global warming increases the frequency of wildfires.
Boreal forests are key players in the global carbon cycle because they store 30–40% of terrestrial carbon. They have been carbon sinks, mainly because they accumulate large amounts of carbon in the form of organic soils. Their net carbon balance is driven by natural wildfires, which produce large carbon emissions approximately every 70 to 200 years, and which are necessary to maintain the productivity and biodiversity of these forests. But climate change is likely to shorten the period between fires (the fire-return interval) by producing warmer temperatures, more lightning strikes, longer wildfire seasons and drier forest conditions than those seen at present, the increase in fire frequency might turn boreal forests from carbon sinks into carbon sources.
The cause of this shift is due to the impact of more-frequent fires on legacy carbon — the organic carbon that has escaped earlier fires and has accumulated at the surface of boreal- forest soils. A boreal forest will act as a carbon sink if a fire removes less soil carbon than the amount that accumulated after the previous fire — or, to put it another way, if the soil carbon removed by a fire is younger than the community of trees affected by the fire.