Marshy Spruce Forests of the Zapadnodvinsky District of the Tver Region: Structure of Forest Stands and Peat Deposits

Swamp spruce forests growing on eutrophic peatlands with mixed water-mineral nutrition can vary in the composition of tree layer species and the structure of the peat deposit during succession changes. Sample plots were created in two swamp spruce forests: swamp-grass (PP1) and swamp-broadleaved-herbs-green-moss (PP2) in the Velessky forestry of the Zapadnodvinsky district of the Tver region. The research is aimed at studying the age, renewal, fallen trees and dynamic characteristics, structure of peat deposits and successional dynamics of swamp spruce forests. The studied swamp spruce forests are unevenly-aged mixed communities of complex vertical structure, consisting of Norway spruce ( L.), black alder ( L.), downy birch ( L.), rarely aspen ( L.), but with a significant predominance of spruce. Uniformity of tree volumes distribution in age generations in ascending or descending order determines the tendency of the correlation between age and tree volumes, tending to maximum values, up to the functional one (R = 0.936). The more uniform the values of tree volumes in generations of age series of forest stands, the closer the correlation of the indicators. The species composition’s change dynamics of forest stands is associated with the moisture values in the community area. The soils of the swamp spruce forests are lowland peat (Fibric Histosols Eutric), composed of thick (up to 5 m) sedge-woody peats in the swamp-grass spruce forest and woody peats (up to 2 m) with a high degree of decomposition (25-45%) in the swamp-broadleaved-herbs-green-moss spruce forest. In swamp spruce forests with mixed composition of tree species intensive processes of the forest stands’ composition’s purification take place, resulting in displacement of deciduous species and formation of pure spruce biogeocenoses, close to climax phases of dynamics. With similarity of the swamp spruce forests’ peat soils’ structure, small differences in the degree of decomposition, ash content, density can still be noted, which are explained by the features of the relief and hydrological regime of the territories.