Syntaxonomy of larch open woodlands on West-Siberian plain

Larch open woodlands fr om West Siberian forest-tundra zone are described based on 119 original rele­vés performed by authors in 2009–2016 years in central part of the West Siberian plain between 65.5–67.5° N (Fig. 1). In spite of tree layer presence these open woodlands are placed into Loiseleurio-Vaccinietea class. This was done due to light and open tree layer; high constancy of hypoarctic species (Betula nana, Arctous alpina, Flavocetraria cucullata, Aulacomnium turgidum,etc.); absence of typical boreal forest species like Linnea borealis, Trientalis europaea, Lycopodium annotinum;active cryoturbations in topsoil.This opinion is supported by previous publications (Norin, 1979; Tyrtikov, 1983; Ilyina, 1985a, b) wh ere northern larch open woodlands were considered as zonal vegetation and special vegetation type for the circumpolar forest-tundra zone. Unlike East Siberian larch open woodlands, which previously were described in alliance Cladonio stellaris–Laricion gmelinii, order Vaccinio–Pinetalia pumilae (Anenkhonov, Chytrý, 1998), the West Siberian ones differ significantly fr om the latters by absence of the large set of regional East Siberian diagnostic species. That is why new alliance Betulo nanae–Laricion sibiricae is suggested for these communities.Group of its diagnostic species includes hypoarctic species (Flavocetraria cucullata, Pedicularis labradorica) and regional species (Larix sibirica, Betula nana, Salix phylicifolia). Nomenclature type (holotypus) — ass. Betulo nanae–Laricetum sibiricae ass. nov. hoc loco. Syntaxonomical diversity of new alliance consists of four associations and two subassociations (all new). This set of syntaxa covers all well-drained habitats across West Siberian forest-tundra zone. Three associations occur on loamy soils and one — Arctostaphylo uvae-ursi–Laricetum sibiricae (nomenclature type (holotypus hoc loco): Table 4, relevé 7 (field number L10–232), 66.02331° N, 75.94489° E, 16.07.2010; diagnostic species: Arctostaphylos uva-ursi, Juniperus communis, Hierochloл alpina) on sandy soil. Typical ass. Betulo nanae–Laricetum sibiricae (nomenclature type (holotypus hoc loco): Table 1, relevé 8 (field number L10–178), 67.00899° N, 79.47630° E, 11.07.2010; Fig. 2; diagnostic species are the same as for the allance) occurs in all parts of forest-tundra zone. Communities of ass. Tofieldio coccineae–Laricetum sibiricae (nomenclature type (holotypus hoc loco): Table 2, relevé 5 (field number L12–434), 67.08792° N, 79.03510° E, 11.08.2012; Fig. 3; diagnostic species: Eriophorum vaginatum, Juncus biglumis, Petasites frigidus, To­fieldia coccinea, Aulacomnium turgidum) occur only near the northern tree limit. Open woodlands of the ass. Equiseto sylvatici–Laricetum sibiricae (nomenclature type (holotypus hoc loco): Table 3, relevé 7 (field number L10–204), 66.30270° N, 79.27226° E, 13.07.2010; Fig. 4; diagnostic species: Picea obovata, Equisetum sylvaticum, Vaccinium myrtillus, Aulacomnium palustre) are distributed mainly in the southern part of forest-tundra zone in transition to northern taiga subzone. Ass. Arctostaphylo uvae-ursi–Laricetum sibiricae is divided into two subassociations due to their geographical location and habitat moisture. Communities of the subass. Arctostaphylo uvae-ursi–Laricetum sibiricaetypicum (nomenclature type and diagnostic species are the same as for the association; Fig. 5) occupy dryer habitats in the northern part of forest-tundra zone, while these of the subass. Arctostaphylo uvae-ursi–Laricetum sibiricaepinetosum sibiricae (nomenclature type (holotypus hoc loco): Tab­le 4, relevé 12 (field number L13–474), 65.98973° N, 78.55362° E, 19.08.2013; Fig. 6; diagnostic species: Pinus sibirica, Carex globularis, Arctocetraria andrejevii) occur southerner in wetter habitats.

Comparison of new syntaxa with previously described larch woodlands from north-eastern part of European Russia (Kucherov, Zverev, 2010) shows that European woodlands most probably belong to the same alliance as West Siberian ones but should be described as separate associations (Table 5). Larch forests with lichen cover described from West Siberian northern taiga (Ermakov, Makhatkov, 2011) differ significantly from larch woodlands and should be placed into boreal forest class Vaccinio-Piceetea.

Geographically new alliance covered the whole West Siberian forest-tundra zone from northern part of northern taiga subzone down south to southern part of southern tundra subzone up north. Eastern border of alliance distribution area is on western Taymyr and western lim it includes north-eastern part of European Russia together with Polar Ural.