Communities with shrub willows in typical tundra subzone in the East European sector of the Arctic

Outside the Russian Arctic, the floristic classification of willow scrub was carried out in Norway (Nordhagen, 1943), Greenland (Daniёls, 1982; Sieg et al., 2006), and Alaska (Cooper, 1986, 1989; Walker et al., 1994; Schickhoff et al., 2002). In the Russian Arctic, willow communities are most fully studied in Chukotka and Wrangel Isl. (Sekretareva, 1990, 1991, 1992, 1995, 2003, 2006; Sinelnikova, 2001); several associations are described in the Siberian Arctic (Zanokha, 2003; Telyatnikov et al., 2014, 2015), on the Kola Peninsula (Koroleva, 2006, 2014), while such studies have just begun in the East European tundras (Neshataev, Lavrinenko, 2020). Many researchers faced a dilemma as to which higher units should be assigned to the syntaxa of communities with shrub willows. They were placed in the Betulo-Adenostyletea Br.-Bl. 1948 (synonym Betulo carpaticae–Alnetea viridis Rejmánek ex Bœuf, Theurillat, Willner, Mucina et Simler in Bœuf et al. 2014), Salicetea purpureae Moor 1958, Scheuchzerio palustris–Caricetea fuscae Tx. 1937 nom. ambiguum (in cases of waterlogging) or Loiseleurio procumbentis–Vaccinietea Eggler ex Schubert 1960 (with a significant abundance of tundra species). Shrub willows are one of the most active plants in the southern and typical tundras of the East European sector of the Arctic. They not only form thickets with an independent high layer (willow scrub), but are also part of tundra and mire communities, in which they are located in one layer (up to 30 cm height) with herbs and dwarf-shrubs. We described 6 associations based on the analysis of 54 relevés made in 12 sites (Fig. 1) of the typical tundra subzone on the Kolguyev, Dolgiy and Vaygach islands and in the tundra near the Pechora River. Some of the described communities with Salix spp. can rightfully be called willow scrub. These are rather high (from 30 cm in height in the northern area of the typical tundra subzone to 160 cm in the southern) and closed (willow cover — 60–95 %) herb- or herb-moss rich thickets mainly from hypoarcto-montane species Salix glauca s. str. and S. lanata s. str. Three new associations are described. Ass. Polemonio acutiflorum–Salicetum lanatae Zanokha ex Lavrinenko et Lavrinenko ass. nov. hoc loco (Table 1, rel. 1–5; Table 5, syntaxon 1; Fig. 2a and b, 3; nomenclature type (lectotypus) — Zanokha, 2003: 35–37, Table 2, rel. 6). Low-growing willow scrub from Salix lanata (30–40 cm height) with herb (Arctagrostis latifolia, Artemisia tilesii, Bistorta vivipara, Cardamine pratensis subsp. angustifolia, Cerastium jenisejense, Equisetum arvense s. l., Myosotis asiatica, Petasites frigidus, Polemonium acutiflorum, Ranunculus propinquus, Saxifraga cernua, S. hirculus, Valeriana capitata)-moss (Brachythecium salebrosum, Bryum pseudotriquetrum, Calliergonella lindbergii, Hylocomium splendens, Plagiomnium ellipticum) cover occupy large areas (up to several hundred square meters) on slightly sloping (1–5 °) sea terraces of Vaygach Isl. in places where sufficient snow accumulates in winter, on terrace bends, in depressions between ridges, on gentle slopes in valleys of small streams (Fig. 2a and b). The soils are cryogenic-ferruginous gley (Fig. 3). The association is also common in typical tundra of the Taimyr Peninsula. Ass. Triseto sibirici–Salicetum glaucae ass. nov. (Table 1, rel. 6–12, nomenclature type (holotypus) — rel. 10 (author’s number — 31_12), Kolguyev Isl., middlestream of the Bugryanka River, 07.08.2012, authors — O. V. Lavrinenko, I. A. Lavrinenko; Table 5, syntaxon 2; Fig. 4a and b, 5). Willow scrub mainly from Salix glauca (70–160 cm height) with herb (Caltha palustris, Carex aquatilis subsp. stans, Comarum palustre, Equisetum arvense s. l., Myosotis palustris, Petasites frigidus, Polemonium acutiflorum, Ranunculus propinquus, Rubus chamaemorus, Stellaria calycantha, S. crassifolia, S. palustris s. l., Trisetum sibiricum, Valeriana capitata)-moss (Brachythecium mildeanum, B. reflexum, Calliergon giganteum, Plagiomnium ellipticum, Rhizomnium pseudopunctatum, Sanionia uncinata) cover are described on Kolguyev Isl. The communities are widespread both in the floodplain, where they occupy flat areas in the middle part and near-terrace depressions (in front of the main bank), and on watersheds — in shallow runoff troughs, in saddles between hills and in the lower parts of slopes (Fig. 4a). The soils are cryogenic-ferruginous gley (Fig. 5). Ass. Climacio dendroidis–Salicetum lanatae ass. nov. (Table 2, rel. 1–20, nomenclature type (holotypus) — rel. 8 (author’s number — 63_12), Kolguyev Isl., middlestream of the Bugryanka River, 15.08.2012, authors — O. V. Lavrinenko, I. A. Lavrinenko; Table 5, syntaxa 3–5; Fig. 6a, b and c, 7). Dwarf-shrub–herb–moss willow scrub dominated by low Salix lanata (up to 50 cm height) and mosses (Climacium dendroides, Hylocomium splendens and Sanionia uncinata) are found exclusively on floodplain terraces, at the confluence of streams and on river bends, and are flooded in the strongest floods, which is well demonstrated by layered soils (Fig. 7). They are recognizable due to their well-defined hillock-hollow microrelief, which creates conditions for the growth of different ecology species. The communities are floristically rich (Table 6), especially in herbs (Alchemilla murbeckiana, Astragalus alpinus subsp. arcticus, Bartsia alpina, Carex aquatilis subsp. stans, Equisetum scirpoides, Euphrasia frigida, Festuca ovina, Pachypleurum alpinum, Parnassia palustris, Polemonium acutiflorum, Potentilla crantzii, Rubus chamaemorus, Valeriana capitata, Viola biflora). The presence of dwarf-shrubs (Arctous alpina, Empetrum hermaphroditum, Salix nummularia, S. reticulata, Vaccinium uliginosum subsp. microphyllum) with a relatively high abundance (10–40%) is a characteristic feature of this association. Subassociations were identified based on floristic differences caused by different stages of succession: C. d.–S. l. typicum subass. nov. (Table 2, rel. 1–13; Table 5, syntaxon 3; Fig. 6a and b, 7); C. d.–S. l. inops subass. nov. (Table 2, rel. 14–20, nomenclature type (holotypus) — rel. 18 (author’s number — 68_05), Kolguyev Isl., downstream of the Peschanka River, 04.09.2005, authors — O. V. Lavrinenko, I. A. Lavrinenko; Table 5, syntaxon 4; Fig. 6c). Communities of a subassociation depleted in species were formed on a younger alluvium in comparison with the typical subassociation. These 3 associations are united into a new alliance. All. Polemonio acutiflorum–Salicion glaucae all. nov. Willow scrub predominantly from Salix glauca and S. lanata with herb or herb-moss cover in depressions, runoff troughs, on the slopes of hills on watersheds and on occasionally flooded floodplains in the European part of the Russian Arctic. Nomenclature type of alliance (holotypus) — ass. Triseto sibirici–Salicetum glaucae ass. nov. (Table 1, rel. 6–12; Table 5, syntaxon 2) described in typical tundra on Kolguyev Isl. Diagnostic species of the alliance: Salix glauca and S. lanata (such species of the Salicetalia glauco-lanatae Bœuf et al. Ex Mucina et Daniёls in Mucina et al. 2016 order), herbs — Petasites frigidus, Polemonium acutiflorum, Poa pratensis s. l., Ranunculus propinquus, Valeriana capitata and moss Hylocomium splendens. High-constant species: herbs — Bistorta vivipara, Carex aquatilis subsp. stans, Equisetum arvense s. l., Rubus chamaemorus and mosses — Bryum pseudotriquetrum, Sanionia uncinata. The alliance is placed in the Salicetalia glauco-lanatae order and conditionally, following L. Mucina et al. (2016), into the Betulo carpaticae–Alnetea viridis class. We believe that new syntaxonomic units of the highest level are needed for scrub communities in the Arctic. This is evidenced by floristic differences. So, among the diagnostic species of this class (a total of 47 species, including 17 of the genus Salix), only 5 are found in the East European sector of the Arctic — Alnus fruticosa, Salix hastata, S. phylicifolia, Cortusa matthioli and Viola biflora, which are not in any way significant in willow scrub, in particular, the Polemonio acutiflorum–Salicion glaucae alliance. It is problematic to position another part of the described communities with Salix spp. as willow scrub even with high shrub cover. Willows do not form the highest of the dominant layers, affecting the composition of the lower layers, in which sedges, some mire grasses and mosses are significant. Communities with Salix myrsinites and other hemicalcephilic species were assigned to 2 associations. Ass. Carici redowskianae–Salicetum myrsinitae ass. nov. (Table 3, rel. 1–6, nomenclature type (holotypus) — rel. 4 (author’s number — 123_04), east coast of Dolgiy Isl., 11.07.2004, authors — O. V. Lavrinenko, I. A. Lavrinenko; Table 5, syntaxon 6; Fig. 8). Willow–sedge (Carex aquatilis subsp. stans, C. paralella subsp. redowskiana, C. rariflora)–moss communities dominated by low (up to 15 cm height) Salix myrsinites and green mosses (Aulacomnium turgidum, Hylocomium splendens, Sanionia uncinata, Tomentypnum nitens) are developed on base-rich soils in the terraces deflections and are distributed in the northern part of the typical tundra subzone on Vaygach, Dolgiy and Kolguyev islands. The main dominants in the syntaxon — Salix myrsinites, S. reticulata, Tomentypnum nitens, and accompanying species — Carex paralella subsp. redowskiana, Saxifraga hirculus; Cyrtomnium hymenophyllum, Orthothecium chryseon; Cladonia pocillum are hemicalcephytes. Ass. Equiseto palustris–Salicetum myrsinitae ass. nov. (Table 3, rel. 7–14, nomenclature type (holotypus) — rel. 9 (author’s number — Van17), north-west of the Bolshezemelskaya tundra, Vangureymusyur Upland, Khekheganyakha River in the middlestream, 10.07.2017, authors — O. V. Lavrinenko, I. A. Lavrinenko; Table 5, syntaxon 7; Fig. 9a and b, 10a and b). Willow–herb–moss communities dominated by Salix myrsinites (up to 30 cm height), green and sphagnum mosses are developed on base-rich soils in