Phytocoenotical positions of suboceanic heath and wet-meadow plants in boreal-forest zone of European Russia

The study is aimed at revealing changes in phytocoenotical positions of oceanic and suboceanic vascular plant species in different subzones and longitudinal sectors of boreal-forest zone of European Russia in comparison with those in Atlantic and Central Europe. For this purpose, we use the set of 5844 releves made in 1996-2018 (see Fig. 1). We analyze changes in constancy and cover of the two heath-redwood (Calluna vulgaris and Empetrum nigrum s.str.) and 8 mesotrophic wet-meadow suboceanic species, alsoMolinia caerulea, referred to both species groups, and Nardus stricta, closely related to the latter in the observed plant cover. Species positions are checked in vegetation units distinguished by means of the dominant-determinant approach to vegetation (see Table 1). Geographical changes in species positions are traced following the combinations of these units in rows for analogous habitats in different subzones. The oceanic species either never reach the western borders of Russia (Erica tetralix, Narthecium ossifragum), or occur at the easternmost limits of their distribution along the Gulf of Finland shores (Juncus squarrosus, Myrica gale, Drosera intermedia) or in relict isolates of the Riss-Wurm (Corynephorus canescens, Sieglingia decumbens) or Atlantic (Festuca filiformis) ages. But Calluna vulgaris and Empetrum nigrum s.str., the suboceanic dominants of treeless Atlantic- and Central-European dwarfshrub heaths, are common under the canopy of Scots pine forest and/or on peatmoss hillocks and ridges in raised bogs of East Fennoscandia and the North-West of the Russian Plain. Calluna vulgaris prefers warm soils and fails to withstand their prolonged frost penetration. Hence it escapes from bogs but keeps on growing in pine forests in the NorthEast of European Russia. It also occurs in the Upper and Middle Volga areas, reaches the Middle Urals, and penetrates the West-Siberian hemiboreal subzone, with its relict findings also known from the Western Sayan Mts. On the contrary, Empetrum nigrum remains only in bogs in the middle- and southern-boreal subzones of the Dvina-Pechora area. But it reaches the Middle Urals as well and occurs in raised bogs of southern-boreal Western Siberia. The East-European low-sedge meadows with the dominance of Carex nigra originated as a result of integration of mesotrophic sedge-peatmoss mires and matgrass (Nardus stricta) grasslands in the montane belt of the east of Central Europe. Many species which constantly occur in such meadows (Agrostis canina, Carex echinata, Juncus conglomerates, Viola palustris, etc.) also reach the Urals and the Trans-Urals but do not penetrate further eastwards. Carex nigra, Potentilla erecta, and Succisa pratensis serve as exclusions as they also occur in Southern Siberia. In the North-West of Russia, Carex nigra grows not only in meadows but also in Scots pine bog forests. The other two species are typical for both meadows and small-leaved forests which replace the latter in the course of the succession both in European Russia and Western Siberia. The genesis of meadow community types is considered natural because these communities occur at the initial stages of secondary successions, driven by both natural and anthropogenic causes. The decrease in cover of the most of the studied species with an increase of Conrad continentality index, statistically testified by means of Spearman rank correlations rs, typically coincide with the lack of correlation between the cover of these species and the vegetation period warmth supply (see Table 2). As regards mineral nutrition and soil acidity requirements, the studied plants belong to acidophytes, oligotrophic or mesotrophic in cases of heath or wet-meadow plants, respectively. Molinia coerulea is typical for heaths and mires as well as meadows of different types, developed on both acidic soil (with Calluna vulgaris and Nardus stricta) and limestone, in Atlantic and Central Europe. It also occurs in beech, oak, birch-oak, and Scots pine forests on nutrient-poor acidic soil there. But the same species is restricted to aapamires and spring peatmoss pine forests, i. e. minerotrophic conditions, and avoids the oligotrophic ones in northern-boreal Fennoscandia. In the meantime, it grows and is often abundant in oligotrophic pine and birch forests at the initial stages of paludification but avoids the eutrophic conditions in the southern-boreal subzone of NorthWest Russia and the Cis- and Trans-Volga areas. In the Trans-Urals, the species occurs in meadows on rich soil again and even prefers the increased salinity conditions. These contrast changes in soil nutrition preferences in different parts of the Molinia coerulea area in Eastern Europe and Western Siberia influence the character of correlations when testifying the suboceanic character of species ranges. But they are not confirmed by any genetical differences (ITS) and should be explained in terms of species ecology. Dry-grassland records of Nardus stricta which mark its Middle-Pleistocene peri-glacial distribution are known for Eastern Europe. But the main Quaternary migration flows of warmth-demanding suboceanic plant species to the east correspond to the Riss-Wurm interglacial or the Atlantic thermal optimum of the Holocene in European Russia. The West-Siberian parts of areas of Calluna vulgaris, Carex nigra, Potentilla erecta, and Succisa pratensis originated due to the first flow mentioned, and that of Empetrum nigrum due to the second one. Calluna vulgaris also penetrated Karelia and the south of the Kanin Peninsula in the Atlantic period. But many Atlantic migrants from Europe could not achieve their far-off distribution in Siberia because of the preAtlantic Boreal thermal optimum there, preceding that in Europe. Populations of Molinia coerulea, asscociated with the eutrophic and oligotrophic soil, respectively, probably migrated in different areas and periods: the former in the Riss-Wurm interglacial of Siberia and then in the Atlanticum of the European North, and the latter only in the Atlanticum of the Russian Plain. The post-Atlantic species migration has played a minor role in the community flora formation. The paper contains 2 Tables, 1 Figure, and 80 References. The authors are grateful to Dr. S.Yu. Popov (M.V. Lomonosov Moscow State University), Dr. S.A. Kutenkov (Inst. Biology, Karelian Research Centre RAS), and D.Ye. Gimelbrant (Komarov Botanical Institute RAS) for their permissions to use the unpublished releves and to Dr. A.Yu. Korolyuk (Central Siberian Botanical Garden Sb RAS) and Dr. O.V. Sozinov (Yanka Kupala Grodno State University) for their help with finding the necessary published sources. The Authors declare no conflict of interest.

Keywords

Authors

References