Forest Fires Effects on Carbon Stocks and Soil Chemistry in Central Yakutia, Eastern Siberia
This study was conducted to determine the impact of fire on the physical and chemical characteristics of soil as well as on the distribution of soil organic and black carbon stocks in ice-rich permafrost regions in eastern Siberia. Three intact and four burnt forest sites with different ignition years were selected. Volumetric water content did not increase in any of the burnt forests in the top soil layer but moisture accumulated at the bottom of the active layer of older burnt sites. Salt content increased in the active layer following forest fires, but a decade later, the salt increase disappeared, indicating the temporal characteristic of this change. The concentration of Na + and SO4 2- in the active layer of the 4-year-old burnt forest site increased 70% and 49% respectively, while other salts (Mg 2+ and Ca 2+ ) did not show any variation in the other burnt forest sites compared to the intact forest sites. The organic carbon stock in the top 200 cm of soil in the intact forest site (44.0 kg m -2 ) was similar to that in burnt forest sites (41.4-43.7 kg m -2 ). On average, 37% of organic carbon was found in the upper 30 cm of the soil profile for intact and burnt forests. The organic carbon distribution in the top 200 cm soil layer in Central Yakutia was higher than previously reported for other Siberian sites. The highest concentrations of black carbon were found in the upper soil layers (20-40 mg g -1 organic carbon) but concentrations of 10-20 mg g -1 organic carbon were also found in the permafrost (120-200 cm depth) of the intact and burnt forests. There was no variation in black carbon concentration among the sites. The presence of black carbon in the permafrost suggests that the active layer was deeper before and that black carbon accumulated because of fires that occurred at that time.