Phytocoenotical positions of continental betular and subnemoral dark-coniferous forest plants in boreal- and nemoral-forest zones of European Russia and the Urals

This study focuses on revealing changes in the phytocoenotic positions of continental Eurosiberian betular (primarily tall-herb) and subnemoral (“chern”) vascular plant species across different subzones and longitudinal sectors of the boreal and nemoral forest zones of European Russia and the Urals. Betular species, belonging to the Braun-Blanquet class Betulo-Adenostyletea Br.-Bl. 1948, are cold-tolerant plants that grow in subarctic and subalpine mountain birch (Betulapubescens s.ampl.) and Siberian larch (Larix sibirica) forests, open woodlands, and elfin woodlands, as well as in tall-herb meadows and shrub thickets that border these habitats. In contrast, chern species are shade-tolerant forest sophytes typical for both the field and canopy layers of subnemoral dark-coniferous forests dominated by Abies sibirica. These forests form a characteristic altitudinal belt on the windward slopes of low mountains in Southern Siberia and the Southern Urals and occur on permafrost-free, nutrient-rich soils under an ultra-humid climate. We use the set of 6294 releves collected between 1996 and 2024, which are grouped into vegetation units based on the dominant-determinant approach to vegetation classification. These units are further organized into zonal series corresponding to analogous habitats across different zones and subzones. We analyze changes in the constancy and cover of 37 species, including 18 betular and 12 subnemoral species, as well as 7 species that belong to multiple historical “corteges” of vegetation - among them Abies sibirica, Pinus sibirica, and Larix sibirica (See Tables 1-3 in Supplement 3). Geographical shifts in species distributions are traced across different units within the established series. Betular species (Calamagrostis langsdorffii, Veratrum lobelianum, Bistorta major, Delphinium elatum s.l. Aconitum septentrionale, Thalictrum minus s.l., Pleurospermum uralense, Cacalia hastata, Crepis sibirica, etc.) form subalpine tall-herb meadows and also grow in riverine elfin birch woodlands from the Northern to the Southern Urals, as well as in the mountains of Southern Siberia. They penetrate beneath the canopy of open herb-fir woodlands along the alpine timberline from the adjacent subalpine meadows and then spread deep into the dark coniferous forest belt along brooks. In the subnemoral forest belt (if present), betular species coincide with subnemoral species (Diplazium sibiricum, Calamagrostis obtusata, Stellaria bungeana, Atragene sibirica, Ranunculus subborealis, Ribes spicatum s.l., Viola selkirkii, etc.) and relict nemoral species. Betular and subnemoral species (the latter including Schizachne callosa, Bupleurum aureum, Knautia tatarica, Cicerbita uralensis) commonly grow together in hemi-boreal nemoral-herb fir-spruce forests of the Cis-Ural and Trans-Volga regions. These communities likely originated from subnemoral dark-coniferous forests in the past. In the boreal forests of North European Russia, the same species combination is typical of riverine tall-herb spruce forests, as well as birch forests that precede them in successional development. Similar patterns are also observed, to some extent, in aspen forests in the northwest of the Russian Plain and in gray alder riparian thickets. Betular herbs are also common in floodplain meadows. Both betular and subnemoral species occur in broadleaved forests at the southern limits of their distribution. Sub-nemoral species generally do not cross the arctic timberline in their northward distribution. However, many betular species occur in the forest-tundra and the southern hypoarctic tundra subzone, where they are mostly confined to willow thickets with increased winter snow accumulation. The continental character of distribution pattern of most examined species is supported by statistically significant positive Spearman rank correlation coefficients (rs) between species cover and the Conrad continentality index, calculated separately for different zonal series. In contrast, the correlations between species cover and vegetation period warmth supply are generally negative (See Table 1 in Supplement 4), a pattern explained by both species ecology and the history of their late- and postglacial migration. Mesoeutrophic mesophytes and hygromesophytes dominate in both species groups due to their continental affinity. Many species can survive on limestone outcrops both at the center and at the edges of their distribution areas. Although betular and subnemoral species coexist in present-day communities, they migrated during different epochs. Species of the first group, including Larix sibirica, expanded their ranges during the cold but wet final stages of glaciations. In contrast, subnemoral species migrated during relatively warm periods at the beginnings and ends of interglacials. The presence of the same betular species in different community types typically reflects multiple waves of migration. The dispersal of sub-nemoral species is dated to the Boreal period of the Holocene in the Upper Pechora River region and to the Atlantic period in the hemiboreal Trans-Volga area. The distinction of the Kama-Pechora-West Ural subprovince within the West Siberian boreal-forest province appears florogenetically justified in the phytogeographical subdivision. The article contains 1 Figure, 5 Tables, 4 Supplements, 85 References. the authors are grateful to Prof. Dr. J. Paal (Univ. Tartu, Estonia), Dr. S.Yu. Popov (M.V. Lomonosov Moscow State University), and D.E. Gimel-brant (Komarov Botanical Institute RAS) for their permissions to use the unpublished releves and to Prof. Dr. D.I. Nazimova (Forest Institute, Siberian Branch RAS), Prof. Dr. N.V. Stepanov (Siberian Federal University), Prof. Dr. O.G. Baranova (Komarov Botanical Institute RAS), and Dr. S.A. Senator (Central Botanical Garden RAS) for their most valuable consultations in the course of preparing this article. The Authors declare no conflict of interest.

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