Carbon Stock in Sandy and Loamy Soils of Coniferous–Broadleaved Forests at Different Succession Stages

A comparative assessment of the carbon stock in loamy soils (Albic Retisols) of coniferous–broadleaved forests on the Moskvoretsko-Oksky Plain and sandy soils (Albic Podzols) in the Bryansk region is given. The carbon accumulation in soils is related to the texture of their mineral horizons and biotic factors, such as the quality of litter and activity of earthworms. The forests on sandy soils were characterized by a high carbon stock in the plant litter, which is explained by the low biomass of earthworms. The carbon content was significantly higher in the mineral horizons of loamy soils owing to high share of fine particles. The carbon stock in the litter and mineral horizons of loamy and sandy soils turned out to be comparable, except for the sandy soils of mixed forests due to higher clay content. In the course of succession of the coniferous-deciduous forests on the loamy soil, the carbon accumulation in the litter was high only at the late stage due to the high input of spruce needles. The carbon stock in the humus horizons of the loamy soils varied due to changes in their density, which was regulated by earthworms. When comparing different succession stages/types of the forests on sandy soils, it was found that the carbon stock in the litter of the pine forests at the early stage of succession was significantly higher than that of the mixed and broadleaved forests. Trends of carbon accumulation in the mineral horizons of sandy soils were mainly explained by their thickness, which was related to the amount of percolating precipitation regulated by woody plants.