The Features of Floristic Composition and Community Structure of the Birch Forests in the Forest-to-Bog Ecotones in the South of the Vasyugan Plain

Abstract

The present study addresses the floristic composition and ecological and community structure of paludified birch forests (peat depth reaching 30 cm) in the southern taiga. The growing conditions were evaluated based on the indicator values of plants and soil chemical properties. The study plots were located on transects directed from upland forests through peripheral wetland forests to bogs, which are situated in topographic lows, at the North-East edge of the Great Vasyugan mire. The sites of the forest-to-bog ecotone that are transformed to various degrees by the bog water regime are considered as successive stages of paludification. Because of the high carbonate content of the soil-forming rocks dominated by heavy clay particles and waterlogging by ground-mire waters, wet green forests without a developed moss cover form here on rich peat-humus soils at the initial stages of hydromorphic transformation of the plant community. This is in contrast to typical plant successions, which develop on carbonate-free sediments and whose development is associated with the effect of acid bog waters. Reed grass (Calamagrostis phragmitoides C. Hartman) dominates the ground vegetation, which also includes sedges (Carex canescens L., C. vaginata Tausch., C. disperma Dew.). The high contents of mineral nutrients in organics-accumulating dark humus soils determines the high floristic diversity of paludified birch forests, comparable with the diversity of upland communities. A significant part of the ground cover of these forests (25% of the species composition, up to 50% of the projective cover) is represented by nutrient-demanding forest- and meadow-swamp plant species, which commonly occur in eutrophic boreal forested swamps of West Siberia with groundwater input. These species are absent in the mesotrophic paludified taiga forests. At a later stage of hydromorphic transformation, pine-birch shrub-moss forests form on peat-humus-gley and peat-gley soils. As the nutrient availability of soils declines, the number of plant species decreases, and plant species with lower nutrient requirements begin to predominate. This leads to the ecological restructuring of wet communities and makes them similar to paludified forests on carbonate-free sediments; peat accumulation begins with the deposition of mesotrophic peat. Thus, a more substantial change occurs in the ecological structure of plant communities on high-carbonate clays during their hydromorphic transformation compared to the typical mesotrophic paludification of dark-coniferous forests on loams

Keywords

• paludified forests
• forest-to-bog ecotones
• floristic diversity
• ecological structure
• community structure
• indicator values of plants
• phyto-indication
• west siberia