Half-Century Dynamics of Plant Communities in Primeval Middle-Taiga Spruce Forests

The objectives of this study were to analyse the vegetation dynamics of the herb-dwarf shrub and moss-lichen layers in the primary spruce forests of the Vepsian Forest Reserve based on data from comprehensive stationary studies on permanent sample plots (PSPs) from 1973 to 2019. It was shown that the vegetation composition of the herb-dwarf shrub and moss-lichen layers and the quantitative ratio of species were determined primarily by the soil moisture regime and the composition and structure of the tree layer. Based on the ordination analysis, differences in the species composition and dynamics were revealed in three types of plant communities generalised by the moisture regime and successional status: (1) drained bilberry spruce forests, (2) excessively moist bilberry-sphagnum and long-stem moss-bilberry spruce forests, and (3) drained bilberry spruce forests with a significant participation of deciduous tree species. Differences were manifested in the endogenous successional dynamics of biogeocenoses with or without a change in the predominant tree species in the period before 1982, as well as during recovery after disturbances in the form of windfall, windfall, and partial dieback of trees, which affected to varying degrees the stands of the studied SPPs and, consequently, the vegetation of the lower layers. The dynamics of vegetation in the herb-dwarf shrub and moss-lichen layers decreased over the study period since 1973 in the following order: drained mixed-species spruce forests, drained pure spruce forests, and overwatered spruce forests.