Charcoal in boreal forest soils in Scandinavia is easier to break down than previously thought, according to a study published online this week in Nature Geoscience. Forest fires convert a fraction of the burning vegetation into charred residues, which have been considered difficult to break down, and therefore a potential long-term carbon sink.

Mikael Ohlson and colleagues sampled hundreds of boreal forest soils in Norway and Sweden, and found that the charcoal content varies considerably between samples. Radiocarbon dating revealed that the charcoal has a median age of 652 years, which is younger than they expected, given that forest fires have been occurring in the region for the past 10,000 years.

Despite the relatively rapid turnover time, the researchers estimate that, if these results are applicable to other soils, the charcoal sink in boreal forest soils amounts to 1 peta gram of carbon, which is equivalent to 1% of the plant carbon stock in boreal forests.