Steppes of the class Cleistogenetea squarrosae Mirkin et al. ex Korotkov et al. 1991 in Eastern Transbaikalia
Transbaikalia is the vast region in Southern Siberia which includes numerous mountain ridges within the upper basins of the three big rivers, the Amur (Pacific Ocean basin), the Yenisey, and the Lena (Arctic Ocean basin). The most part of Transbaikalia territory is covered by woodlands, however, the steppes are an inherent component in the southern part of the region. Due to broad distribution they form the steppe and forest-steppe altitudinal belts in the mountains, and even totally predominate in the vast plains of the southeastern part of studied territory. Steppe communities occur throughout the broad range of habitats varying in humidity, edaphic conditions, and anthropogenic disturbance. There is a lack of any established opinion on Trans-baikalian steppe classification among the Russian botanists (Reshchikov, 1961; Lavrenko et al., 1991; Dulepova, 1993). The syntaxonomy of east-transbaikalian steppes has not been developed yet. The steppes of this region are represented in few publications covering small territories. T. L. Arbuzova and B. I. Dulepova (1989) described three associations from the Sokhondo Biosphere Reserve, which were attributed to the class Cleistogeneta squarrosae Mirkin et al. ex Korotkov et al. 1991. The main aims of my study are: (1) to propose a phytosociological classification of east-transbaikalian steppes and to characterize the syntaxa distinguished, (2) to reveal principal ecological factors that have an influence on regional syntaxonomical patterns of the steppe vegetation in Transbaikalia. All transbaikalian steppes belong to the class Cleis-togenetea squarrosae. The class represents main dry grassland diversity of the East Siberian-Central Asian sector of Palaearctic (Hilbig, 1995; Korolyuk, 2002). This class consists of two orders: Helictotrichetalia schelliani Hilbig 2000 (meadow steppes and rich-in-species bunchgrass steppes of mountain forest-steppe), and Stipetalia krylovii Kononov, Gogoleva et Mironova 1985 (typical bunchgrass steppes of the steppe zone and mountain steppe belt). Alliance Stipion krylovii includes non-petrophytic steppes which are common mainly in the steppe belt and the steppe zone. In Eastern Transbaikalia it is represented by two associations. Ass. Potentillo semigla-brae-Stipetum grandis ass. nov. (Table 1; holotypus hoc loco - releve 4 (09-349): Trans-Baikal Territory, Ononskiy district, north coast of Zun-Torey Lake, N 50.16447°, E 115.84509°, 22.07.2009, author - A. Yu. Korolyuk) is common in south-eastern part of Trans-Baikal Territory and in the adjacent regions of Mongolia. It unites more xerophytic variants of zonal steppes dominated by bunchgrasses and rhizomatous Leymus chinensis. Ass. Artemisio laciniatae-Ley-metum chinensis ass. nov. (Table 1; holotypus hoc loco - releve 13 (09-436), Trans-Baikal Territory, Ononskiy district, Daurskiy Nature Reserve, the plain between Nizhniy Mukey Lake and Imalka River, N 49.99331°, E 115.25308°, 29.07.2009, author - A. Yu. Korolyuk) includes typical steppes which are developed on soils under occasionally influence of ground waters. It causes low salinization of the upper soil horizons and high frequency and abundance of salt tolerant plants - caespitose Iris lactea and rhizoma-tous Leymus chinensis, Thermopsis lanceolata, Artemisia laciniata. Alliance Thymion gobici Mirkin et al. ex Hilbig 2000 comprises xerophytic petrophyte steppes of Transbaikalia, Central and Eastern Mongolia, Inner Mongolia province (China). In Eastern Transbaikalia it is represented by single ass. Ptilotricho dahurici-Arctogerontetum graminei ass. nov. (Table 1; holotypus hoc loco - releve 29 (09-327), Trans-Baikal Territory, Aginskiy district, west coast of Nozhiy Lake, N 50.83191°, E 114.80023°, 21.07.2009, author - A. Yu. Korolyuk). Into this association, I includes polydominant rich xerophytic petrophyte steppes that are characterized by high abundance of short-growing perennial herbs, often with cushion growth form. Order Helictotrichetalia