Zonal vegetation of the plain East European tundras

Zonal tundra vegetation occupies slightly sloped watershed surfaces, weakly convex tops and gentle slopes of moraine hills and ridges with moderate snow cover and loamy soils (plakors). Environmental conditions of such sites are most relevant to macroclimate (Aleksandrova, 1971; Matveyeva, 1998). For the East European sector of the Arctic this vegetation was described in 30–70 years of last century by the Soviet geobotanists V. D. Aleksandrova (1956), ­ V. N. Andreyev (1932), I. D. Bogdanovskaya-Giye­nef (1938), A. A. Dedov (2006), A. E. Katenin (1972), Z. N. Smirnova (1938), who, following the dominant approach, attributed the described associations mainly to the moss vegetation type. In the Asian sector of the Arctic (Yamal and Taymyr peninsulas, Arctic Yakutia, Wrangel Isl.) and in Alaska some associations of zonal communities with Carex bigelowii s. str., C. bigelowii subsp. arctisibi­rica and C. lugens have been described according to Braun-Blanquet approach: Carici arctisibiricae–Hylocomietum alaskani Matveyeva 1994, Dryado integrifoliae–Caricetum bigelowii Walker et al. 1994, Salici polaris–Hylocomietum alaskani Matveyeva 1998, Carici lugentis–Hylocomietum alaskani Sekretareva 1998 ex Kholod 2007, Salici polaris–Sanionietum uncinatae Kholod 2007, Tephrosero atropurpureae–Vaccinietum vitis-idaeae Telyatnikov et Pristyazhnyuk 2012, Festuco brachyphyllae–Hylocomietum alaskani Lashchinskiy ex Telyatnikov et al. 2014. Our study area in the East European tundras (730 km of south–north and 550 km of west–east directions) covers 3 tundra subzones (arctic, typical and southern) and two floristic subprovinces (Kanin-Pechora and Ural-Novaya Zemlya) (Fig. 1). 7 associations (one with 5 subassociations) based upon 101 authors’ relevés as well 95 ones by geobotanists-predecessors were described or validated on plakors and habitats close to these. Zonal communities are comprised by thick multi-species moss layer formed by mesophylous bryophytes (Aulacomnium turgidum, Hylocomium splendens, Ptilidium ciliare, Racomitrium lanuginosum and Tomentypnum nitens), the presence of Carex bigelowii subsp. arctisibirica, Deschampsia borealis or D. glauca in the herb layer, the high abundance of dwarf-shrubs, the presence, but not always, of Dryas octopetala and shrubby willows. Their plant cover is closed or discontinuous with frost-boils (3-component module of patch of bare ground – rim – trough or 2-component one of flat surface – patches of bare ground — see Fig. 2, 3). Zonal syntaxa are the richest in species number, compare to all others because the placor habitats are moderate in such important environmental characters as moisture and nutrition of soil and snow depth. That’s why they contain, with the same constancy and sometimes abundance, some character species of alliances and classes of intrazonal vegetation: Kobresio-Dryadion Nordh. 1943 (dryad fell-fields on well drained snowless or poor snowy habitats with slightly carbonated loamy-gravelly soils at outcrops of bedrock) and Carici rupestris–Kobresietea bellardii Ohba 1974, Loiseleurio-Arctostaphylion Kalliola ex Nordhagen 1943 (dwarf-shrub and dwarf-shrub-lichen (often with Betula nana) communities on sandy soils) and Loiseleurio procumbentis–Vaccinietea Eggler ex Schubert 1960, Rubo chamaemori–Dicranion elongati Lavrinenko et Lavrinenko 2015 (dwarf-shrub-cloudberry-moss (Dicranum elongatum, Polytrichum strictum)-lichen communities of oligotrophic palsa and polygon peatlands) and Oxycocco-Sphagnetea Br.-Bl. et Tx. ex Westhoff et al. 1946. The basic syntaxon, whose communities occupy the placor habitats in the arctic tundra subzone (southern­ variant) is Salici polaris–Polytrichetum juniperini Aleksandrova 1956, described on the Southern Island of Novaya Zemlya (Table 1). Similar syntaxa in the typical tundra subzone are Carici arctisibiricae–Hylocomietum splendentis Andreyev 1932 nom. mut. propos. hoc loco (Table 5, Fig. 14–17) and Dryado octopetalae–Hylocomietum splendentis Andreyev 1932 nom. mut. propos. hoc loco salicetosum nummulariae (Bogdanov­skaya-Giyenef 1938) subass. nov. (stat. nov.), nom. corr. hoc loco, described by us and earlier by I. D. Bogdanov­skaya-Giyenef (1938) and Z. N. Smirnova (1938) on the Kolguyev Isl. (Table 2, Fig. 3, 5, 6); D. o.–H. s. caricetosum redowskianae subass. nov. hoc loco and D. o.–H. s. caricetosum arctisibiricae (Koroleva et Kulyugina in Chytrý et al. 2015) subass. nov. (stat. nov.) hoc loco (Table 4, Fig. 4, 9–13) — in the most eastern part of the studied area (Vaygach Isl., Yugorskiy Peninsula and Pay-Khoy Range); D. o.–H. s. typicum subass. nov. hoc loco (Tab­le 3), described by us with use the V. N. Andreyev (1932) relevés on Vangureymusyur Upland (Bolshezemelskaya tundra). In the southern tundra subzone the basic zonal association is Calamagrostio lapponicae–Hylocomietum splenden­tis ass. nov. hoc loco (Table 6, Fig. 20–22). Even small deviations from placor habitat conditions are reflected in the community species composition. In such habitats the following syntaxa are described: Deschampsio borealis–Limprichtietum revolventis Aleksandrova 1956 nom. mut. propos. hoc loco and Flavocet­rario nivalis–Dryadetum octopetalae Aleksandrova 1956 nom. mut. propos. hoc loco on gentle slopes and loamy soils, not in moderate soil moisture, but in wet or, on the contrary, well-drained ecotopes on the Novaya Zemlya (Table 1); Dryado octopetalae–Hylocomietum splendentis caricetosum capillaris subass. nov. hoc loco — on the deluvial tails, in the mid and lower parts of the gentle slopes in Bolshezemelskaya and Malozemelskaya tundras (Table 4, Fig. 2, 7, 8); Oxytropido sordidae–Hylocomietum splendentis ass. nov. hoc loco — in the Pakhancheskaya Bay area (the northern part of the Bolshezemelskaya tundra) on strongly sloping well drained slopes (Table 6, Fig. 18, 19). We attributed these syntaxa to zonal vegetation due to the presence of such taxa of its differential combination as shrub Salix glauca, dwarf-shrub Salix polaris, herbs Bistorta major, Carex bigelowii subsp. arctisibirica, Deschampsia borealis, D. glauca, Eriophorum brachyantherum, Juncus biglumis, Luzula arcuata, Pedicularis lapponica, Petasites frigidus, Poa arctica, Saxifraga hieracifolia, S. hirculus, Stellaria peduncularis, Valeriana capitata, mosses Aulacomnium turgidum, Hylocomium splendens, Ptilidium ciliare, Racomitrium lanuginosum, Tomentypnum nitens and lichens Lobaria linita, Nephroma expallidum, Protopannaria pezizoides, Psoroma hypnorum. This combination of taxa differentiates (by the presence, constancy, abundance) the zonal communities in studied area from vegetation of other classes (Carici rupestris–Kobresietea bellardii, Loiseleurio procumbentis–Vaccinietea, Oxycocco-Sphagnetea) (Table 7). The borders of many species area distribution are held in the East European tundras, so the variation of the community species composition along the latitudinal and longitude gradients is quite natural. Thus, in zonal communities Ledum palustre subsp. decumbens and Salix phylicifolia occur and Betula nana as well as hypoarctic dwarf-shrubs Arctous alpina, Empetrum hermaphroditum, Vaccinium uliginosum subsp. microphyllum­ and V. vitis-idaea subsp. minus are most active only in the southern tundra subzone; Salix polaris (its activity increases to the north) and, in some syntaxa, Dryas octopetala are common in the subzones of typical and arctic tundras. In zonal conditions shrubs Salix glauca, Betula nana (prostrate) and all hypoarctic dwarf-shrubs occur in the typical tundra subzone on the mainland and on Kolguyev Isl., while in the northern part of this subzone on Vaygach Isl. they are already absent, ­except the Vaccinium spp. (with low constancy). In the arctic tundra subzone there are no shrubs and hypoarctic dwarf-shrubs on plakors, while Salix polaris is abundant. We believe that these floristic differences of zonal communities can be considered as markers of their subzonal affiliation. A similar shift in species distribution on the latitudinal gradient is established (Matveyeva, 1998) for the zonal biotopes on Taymyr Peninsula. Some species (Arctagrostis latifolia, Cerastium regelii subsp. caespitosum, Saxifraga oppositifolia, Silene acaulis) have high constancy in zonal communities within the Ural-Novaya Zemlya subprovince, as opposed to the Kanin-Pechora one. Herbs Oxyria digyna, Papaver polare, Parrya nudicaulis, Pedicularis sudetica subsp. arctoeuropaea, Saxifraga cernua and S. cespitosa occur with high constancy only in zonal communities on Novaya Zemlya that brings them closer to syntaxa described in the arctic and typical tundra subzones on Taymyr Peninsula (Matveyeva, 1994, 1998). Already in 1994, N. V. Matveyeva stated the need to describe a new class for zonal vegetation. The name Carici arctisibiricae–Hylocomietea alaskani cl. prov. has been reserved for this class in Yalta’s conference on the classification of Russian vegetation (Lavrinenko et al., 2016), Prague’s “Circumpolar Arctic Vegetation Archive and Classification Workshop” (presentation by N. V. Matveyeva) and “Arctic Science Summit Week 2017” (Lavrinenko et al., 2017). We do not attribute the newly described syntaxa to alliance Dryado octopetalae–Caricion arctisibiricae Koroleva et Kulyugina in Chytrý et al. 2015, which was described at the base of 15 relevés by geobotanists-predecessors (V. N. Andreyev, A. A. Dedov) and as well the 11 ones by E. E. Kulyugina for zonal habitats in the East European tundras (Koroleva, Kulyugina, 2015). At least, it is necessary to revise this alliance, since the name of ass. Pediculari oederi–Dryadetum octopetalae (Andreev 1932) Koroleva et Kulyugina 2015 are not legitimate (nomen superfluum), ass. Salici reticulatae–Dryadetum octopetalae Koroleva et Kulyugina 2015 need to be revised and the rank of the third one (Dryado octopetalae–Caricetum arctisibiricae Koroleva et Kulyugina in Chytrý et al. 2015 was lowered by us (in this paper) to subass. Dry