Our study plots were in pine forests of Leningrad Region in the following districts: Kurortny, Lodeynopolsky, Lomonosovsky, Luga, and Priozersky. Taxation characteristics of forest stands, species diversity of ground cover, age and type of forest fires (according to plant species composition of ground cover and thickness of annual rings of pines trunks), morphological and general physical and chemical characteristics of soils, stocks of soil organic matter (according to losses during ignition and according to Corg by Turin). The forest floor by sub-horizons (L, F, and H) and the underlying pyrogenic layer were sampled at five points near the base soil pit with a 25x25 cm frame. Mineral horizons were sampled in fivefold replications from the base soil pit. The age of crown fires in the studied pine forests ranged from 60 to 140 years. It was found that the C pools in the forest floor varied in the range of 1.2-3.2 kg/m2 and in the mineral layer of 20 (30) cm 1.5-4.4 kg/m2, in the 1-3 cm pyrogenic layer, containing charcoal and detritus, the 0.3 to 2.1 kg/m2. The choice of modifications of methods for determining the content of hygroscopic water (H2Ohygr, 70 and 105 °С) and losses on ignition (LOI 550 and 900 °С) contributes to the clarification of the obtained values. H2Ohygr differs by a factor of 1.5-2.0 not only with changes in drying temperature, but also it depends on the season (whether the heating in the room is on). The LOI of the soils studied do not depend on the selected temperatures. The conversion coefficient C to organic matter is more often used 1.724, while it has long been suggested to round this value to 2 (Ponomareva and Plotnikova, 1980; Orlov, 1985).
This work was supported by grant 22-24-00690 from the Russian Science Foundation.