Charcoal carbon pools and their persistence in boreal forest soils, Northwest Territories, Canada

Boreal forests store a large proportion of the world’s carbon (C) stocks in forest floor and mineral soils. Fire produces charcoal and other pyrogenic carbon (PyC) compounds that accumulate in soil, representing a poorly understood component of C stocks in boreal regions. Understanding the amount and decay rate of PyC is important for improving the accuracy of C budget models for boreal forests. In this study, charcoal, the predominant component of PyC was extracted and quantified using soil samples collected in the Northwest Territories (NWTs), Canada. The concentration of soil and charcoal C was determined using elemental analysis, while the age of charcoal was ascertained by radiocarbon dating. The proportion of charcoal C relative to total soil organic C was similar in forest floor and <2 mm mineral fractions, averaging 2.2% ± 0.5% and 2.0% ± 0.4%, respectively. Estimates of charcoal C quantities and proportion of the soil organic matter were comparable to other boreal and temperate forests but differed from grasslands. Charcoal ages were on centennial to multi-centennial scales, with charcoal C concentrations negatively correlated with age. Overall, charcoal represents a small but important component of organic C in NWT boreal forest soils and persists for centuries.