LAUSR

The study of the biodiversity of vegetation cover in the context of its genesis and development is an important task. The results of these studies are the basis for the development of ecological, biogeographical, evolutionary, and sociological research, such as modelling the dynamic processes of natural ecosystems, understanding the consequences of natural and anthropogenic changes for biodiversity, solving problems of biodiversity conservation, etc. Of particular interest from this point of view is the biodiversity of ecotones, which can serve as a model for studying the factors of the genesis of the plant cover structure in a dynamic environment. In this paper, we analyze the taxonomic structure of the flora of vascular plants and the spatial structure of the plant cover in the East Asian boreal–nemoral ecotone (of the Lower Amur region). The botanical research was conducted through the application of traditional techniques for floristic and geobotanical studies. The material for this article was drawn from over 15,000 herbarium samples and 1400 floristic and geobotanical descriptions made between 1993 and 2021 in the Lower Amur region. The analyzed flora includes 2240 species from 760 genera and 158 families, which constitute 80% of the species composition of the Russian part of the Amur River basin. The native flora comprises 1801 species from 602 genera and 152 families. The species diversity and quantitative characteristics of the natural and adventive flora of vascular plants in the Lower Amur region are comparable to those of the southern limit of the distribution of taiga ecosystems in the Holarctic. The spectrum of the leading families and genera in terms of the number of species corresponds to the geographical position of the territory (the family spectrum is led by Asteraceae, Cyperaceae, Poaceae, Ranunculaceae, Rosaceae and Polygonaceae and in the generic spectrum, Carex, Artemisia, Salix, Viola, Saxifraga, Poa and Saussurea). The specificity of the flora is determined by a combination of elements in the boreal and sub-boreal flora of East Asia. Seven floristic complexes are defined for the Lower Amur region flora: forest (41.4% of the native flora), meadow (19.2%), mire (4.1%), mountain tundra (12.5%), rocky scree (8.9%), aquatic–semiaquatic (7.8%) and floodplain–estuarine shallow (6.2%). The regularity of some floristic complexes is defined by the landscape’s ecological conditions, and the variety in the edaphic, orographic and climatic parameters within the region. The spatial structure of the plant cover of the boreal–nemoral ecotone is described.