Changes in the Pools of Total and Labile Soil Organic Carbon during Post-Fire Succession in the Khibiny Mountain Tundra Ecosystems

The changes in the total soil carbon storage and the pools of labile and potentially mineralizable organic matter in Entic Folic Podzols of the Khibiny Mountains (Murmansk region, NW Russia) caused by wildfires of high and moderate intensity and during the post-fire succession are discussed. Although a moderate-intensity wildfire has no statistically significant impact on the total soil carbon pool, it triggers the active erosion processes leading to the carbon losses comparable to the direct pyrogenic carbon losses in a high-intensity fire. In the postfire soil restoration, the type of organic carbon accumulation changes: the surface carbon accumulation in the form of peat is characteristic of the control site, while up to half of soil carbon is accumulated in the mineral horizons at late stages of the postpyrogenic succession. A high-intensity fire leads to almost complete destruction of labile, microbial, and potentially mineralizable carbon pools in both the organic (pyrogenic) and mineral horizons. A moderate-intensity fire does not cause any statistically significant changes in these pools as compared to the control. The restoration dynamics of the labile and potentially mineralizable pools of organic matter in the pyrogenic horizons of soil differ: the trend of a steady increase in the pools of labile and microbial carbon is observed for three years after the fire and later, while the pool of potentially mineralizable carbon reaches its maximum three years after the fire and then becomes stabilized at this level.