Impacts of Forest–Peat Fires on Soils and Their Influence on Carbon Losses in Phytogenic Microelevations of Mountain Swamps in the Southern Part of Central Siberia

An assessment of the degree of contrast in the physicochemical properties of pyrogenic peat soils and fire-induced carbon losses 20 years after a major fire that partially destroyed a swamp spruce forest (Picea obovata Ledeb.) located within a complex of small river valleys in Kuznetsk Alatau, Republic of Khakassia, is made. The area affected by the fire is currently occupied by a shrub–sedge–green moss–hypnum birch forest (Betula pubescens Ehrh.) belonging to the group of short-term–secondary postfire grass forests. The pyrogenic peat soils (i.e., mechanical and chemical underburning) that formed as a result of passive smoldering (i.e., thermal impact below the ignition point) feature a high variability of physicochemical parameters (Cv = 26–37%). The application of multivariate statistical analysis techniques (cluster, discriminant, and canonical analysis) has made it possible to distinguish and statistically substantiate four clusters that correlate with the series of pyrogenic peat soils. Organic carbon makes the greatest (83%) input into the total contribution of chemical parameters to the differentiation of clusters, while the input of the volumetric water content is significantly less (15%). Based on the diversity and abundance of fire traces in the profile of pyrogenic peat soils, the distinguished clusters have been conditionally associated with slight, moderate, medium, and strong thermal impacts. Proportionally to the fire impact intensity, the soil clusters are enriched with ash components by 1.6–2.7 times (the ash content varies from 18.9 to 77%) and compacted by 2.2–4.3 times (the bulk weight reaches 0.147–0.421 g/cm³), while their pH value gradually changes from 6.8 to 7.6. A new approach to assessing carbon losses that occur in the course of passive peat smoldering is proposed. The new approach is based on the difference in the carbon content before and after the fire; it supplements the traditional method based on the peat-deposit incineration depth. The additional carbon losses in the 0- to 20-cm layer of pyrogenic peat soils vary in the range from 1.6 to 4.0 kg/m², which is equivalent to 5.9–14.8 kg/m² in CO₂ emissions. The data on additional carbon losses at the stage of passive peat deposit smoldering are presented for the first time.