Carbon Emissions From Fires in Eastern Siberian Larch Forests

Siberian boreal forests have experienced increases in fire extent and intensity in recent years, which may threaten their role as carbon (C) sinks. Larch forests (Larix spp.) cover approximately 2.6 million km² across Siberia, yet little is known about the magnitude and drivers of carbon combustion in these ecosystems. To address the paucity of field-based estimates of fuel load and consumption in Siberian larch forests, we sampled 41 burned plots, one to two years after fire, in Cajander larch (Larix cajanderi) forests in the Republic of Sakha (Yakutia), Russia. We estimated pre-fire carbon stocks and combustion with the objective of identifying the main drivers of carbon emissions. Pre-fire aboveground (trees and woody debris) and belowground carbon stocks at our study plots were 3.12 ± 1.26 kg C m^-2 (mean ± standard deviation) and 3.50 ± 0.93 kg C m^-2. We found that combustion averaged 3.20 ± 0.75 kg C m^-2, of which 78% (2.49 ± 0.56 kg C m^-2) stemmed from organic soil layers. These results suggest that severe fires in Cajander larch forests can result in combustion rates comparable to those observed in North American boreal forests and exceeding those previously reported for other forest types and burning conditions in Siberia. Carbon combustion was driven by both fire weather conditions and landscape variables, with pre-fire organic soil depth being the strongest predictor across our plots. Our study highlights the need to better account for Siberian larch forest fires and their impact on the carbon balance, especially given the expected climate-induced increase in fire extent and severity in this region.