Carici supinae–Betuletea pendulae — new forest vegetation class in steppe zone of West Siberian plain and Transural Plateau

The steppe zone occupies only the southernmost part of West Siberian plain and Transural Plateau, approximately between 54° and 52° N. Zonal communities are species-rich grasslands (Isachenko, Rachkovskaya, 1961; Lapshina, Lavrenko, 1985), but due to relief and geological substrates there are numerous isolated saucer-shaped suffosion depression among flat steppe landscape occupied by small (0.5–1.5 ha) forest massifs. Previously such landscapes were described as “false forest-steppe” or “kolok steppe” following local term “kolok” that is the forest “island”. In some areas such “forest islands” occupy up to 20 % of whole area that makes difficult to identify the border between steppe and forest-steppe zones, in particular in anthropogenically transformed landscape. Until now, there is no information on the structure and floristic composition of such forests, except for brief mentiones in papers on steppe vegetation. The main aim of this paper is to assess the diversity of the deciduous forests in the steppe zone within the study area and establish their syntaxonomical position in the floristic classification. The research is based on 376 original relevés performed by authors in 2007–2016 years in steppe zone from Urals on the west to the Ob river valley on the east. Small intrazonal forest massifs are described as a part of the new class wich contains one order, two alliances and seven associations with four subassociations. Class Carici supinae–Betuletea pendulae class nov. hoc loco. Nomenclature type (holotypus hoc loco) is the order Carici supinae–Betuletalia pendulae ord. nov hoc loco. Diagnostic species: Artemisia austriaca, A. pontica, A. sericea, Carex praecox, C. supina, Festuca rupicola, Medicago falcata, Phleum phleoides, Spiraea crenata, Thymus marschallianus, Veronica spicata, V. spuria; all are mesoxerophytes, most are typical for the steppe class Festuco–Brometea. Order Carici supinae–Betuletalia pendulae ord. nov. hoc loco. Nomenclature type (holotypus hoc loco) is the alliance Sileno nutantis–Betulion pendulae all. nov. hoc loco. Diagnostic species are the same as for class. There are two alliances differing in geographic distribution and habitats within the order. Alliance Sileno nutantis–Betulion pendulae all. nov. hoc loco. Nomenclature type (holotypus hoc loco) is the ass. Sileno nutantis–Betuletum pendulae ass. nov. hoc loco. Diagnostic species: Adenophora lilifolia, Campanula bononiensis, C. wolgensis, Euphorbia subtilis, Galium boreale, Plantago urvillei, Xanthoselinum alsaticum. Association includes deciduous, mostly birch, forests which occur on well-drained plains as small massifs in river valleys and in suffosion depressions. There are four associations differing by habitat moistening within the alliance. Ass. Sileno nutantis–Betuletum pendulae ass. nov. hoc loco (nomenclature type (holotypus hoc loco) — Table 1, relevé 5 (field number L13-035), N 53.09602°, E 60.91305°) unites forests at the base of the northoriented slopes and on the periphery of the large suffosion depressions throughout the class distribution area. Diagnostic species = alliance diagnostic species.) Ass. Pulsatillo patentis–Betuletum pendulae ass. nov. hoc loco (nomenclature type (holotypus hoc loco) —Table 2, relevé 6 (field number L12-134), N 52.46126°, E 60.32398°) includes forest massifs from the driest habitats in the south-western part of the class distribution area near the border between West Siberian plain and Kazakh Upland. Diagnostic species: Achillea nobilis, Antennaria dioica, Gyp- sophila altissima, Helictotrichon desertorum, Hieracium echioides, Onosma simplicissima, Pulsatilla patens, Ve- ronica incana). Subass. Pulsatillo patentis–Betuletum pendulae typicum (Table. 2, relevé 1–13). Physiognomy, no- menclature type and diagnostic species are the same as for the association. Subass. Pulsatillo patentis–Betuletum pendulae populetosum tremulae subass. nov. hoc loco (nomenclature type (holotypus hoc loco) — Table 2, relevé 17 (field number L15-074), N 52.05014°, E 59.14092°) includes small massifs of aspen forest from western border of the class distribution area. Diagnostic species: Artemisia armeniaca, Asparagus officinalis, Fritillaria ruthenica, Hylotelephium stepposum, Myosotis imitata, Populus tremula (dom.), Salvia stepposa, Stipa pennata). Ass. Brachypodio pinnati–Betuletum pendulae ass. nov. hoc loco (nomenclature type (holotypus hoc loco) — Table 3, relevé 8 (field number L13-130), N 55.32487, E 64.62582) may be considered as transitional syntaxon between classes Carici supinae–Betuletea pendulae and Brachypodio pinnati–Betuletea pendulae. Diagnostic species: Brachypodium pinnatum, Calamagrostis arundinacea, Polygonatum odoratum). Association includes two subassociations —Brachypodio pinnati–Betuletum pendulae typicum and Brachypodio pinnati–Betuletum pendulae galietosum tinctorii differing by geographical distribution. Ass. Carici distichae–Betuletum pendulae ass. nov. hoc loco (nomenclature type (holotypus hoc loco) — Table 4, relevé 8 (field number L13-089), N 54.11368, E 61.82870) includes forests in suffosion depressions which are transitional to the class Alnetea glutinosae. Diagnostic species: Calamagrostis canescens, Carex disticha, C. melanostachya, Lysimachia vulgaris, Phalaroides arundinacea, Poa palustris, Ptarmica cartilaginea, Salix cinerea, Veronica longifolia). Alliance Artemisio dracunculi–Betulion pendulae all. nov. hoc loco (nomenclature type (holotypus hoc loco) is the ass. Artemisio rupestris–Betuletum pendulae) includes small massifs of deciduous for- ests in suffosion depressions with poor drainage, more common in eastern part of West Siberian plain. Diagnostic species: Artemisia dracunculus, Berteroa incana, Festuca valesiaca, Glycyrrhiza uralensis, Peucedanum morisonii, Rosa laxa). Alliance includes three associa- tions differing by habitat moistening and anthropogenic pressure. Ass. Artemisio rupestris–Betuletum pendulae ass. nov. hoc loco (nomenclature type (holotypus hoc loco) — Table 5, relevé 5 (field number L16-293), N 53.41704, E 76.61384) includes birch forests in south-eastern part of class the area in suffosion depressions and on ancient lake coastal ramparts. Diagnostic species: Artemisia abrotanum, A. rupestris, Koeleria cristata, Vicia cracca) Ass. Hieracio virosi–Populetum tremulae ass. nov. hoc loco (nomenclature type (holotypus hoc loco): Table 6, relevé 9 (field number L07-021), N 52.92644, E 79.71519). includes aspen or rare birch forests on sandy terraces of salt lakes. Diagnostic species: Chenopodium album, Hieracium virosum, Leonurus glaucescens, Populus tremula, Ribes aureum) Ass. Berteroo incanae–Betuletum pendulae Lashchinskiy et Lashchinskaya 2012 was previously described from Priobskoe plateau (Lashchinskiy, Lashchinskaya, 2012). There is the well-pronounced difference between new class and previously known syntaxa of the alliance Peucedano morisonii–Betulion pendulae which includes the driest communities in the class Brachy- podio-Betuletea. The identified distribution area of the new class covers the northern part of the steppe zone in the southern part of West Siberian plain from Urals to the Ob river valley. Its northern limit coincides quite well with the border between steppe and forest-steppe zones, while southern one does with the forest boundary on West Siberian plain and Transural Plateau.