Fire as a Removal Mechanism of Pyrogenic Carbon From the Environment: Effects of Fire and Pyrogenic Carbon Characteristics

Pyrogenic carbon (PyC, charcoal) is produced during vegetation fires at a rate of ~ 116–385 Tg C yr-1 globally. It represents one of the most degradation-resistant organic carbon pools, but its long-term fate and the processes leading to its degradation remain subject of debate. A frequently highlighted potential loss mechanism of PyC is the consumption of PyC in subsequent fires, however, only three studies to date have tested this hypothesis with reported losses of 300C. Mass losses also showed a significant negative correlation (r=-0.38, p=0.05) with thermal recalcitrance (T50) determined using Differential Scanning Calorimetry (DSC) and Tmax with charcoal reflectance (Ro) determined after the fires (r=0.46, p=0.05). Losses in the high-intensity fire were significantly higher (p=0.05) than in the low-intensity fire, but the latter had a higher rate of conversion of fuel to PyC. Our results demonstrate that exposure to fire can indeed be a significant removal mechanism for PyC that remains exposed on the ground fires. The losses found, however, are likely to represent an extreme upper range as most PyC produced in a fire would not remain exposed on the ground surface by the time the next fire occurs. Our data also demonstrate, for real wildfire conditions, the (i) contrasting resistance of different PyC types to combustion and (ii) contrasting net PyC losses between different fire intensities. The DSC and reflectance results support the usefulness of these analyses in reflecting thermal degradation resistance and temperature exposure under actual