Class Festuco-Brometea Br.-Bl. et Tx. ex Soó 1947 in the Southern Trans-Urals (the steppe zone of Chelyabinsk Region)

The steppe zone covers the southern part of Chelya­binsk Region (38 % of territory). Arable land occupies the main part of the steppe zone, virgin steppes form small scattered patches under grazing and regular fires. Until now there was no enough information on the diversity of steppe vegetation in this region, whereas the steppe syntaxonomy of adjacent regions is rather well developed (Zhirnova, Saitov, 1993; Dubravnaya ..., 1994; Flora..., 2010; Korolyuk, 2014, 2017; Unikalnye..., 2014; Yusupova, Yamalov, 2016; Yusupova et al., 2018; Golovanov et al., 2021). The purpose of present study is to reveal the diversity of the steppes in the Southern Trans-Urals within the steppe zone and to present their classification accor­ding to Braun-Blanquet approach. The investigated area is a high foothill plain, sett­ling on the Trans-Urals peneplain. Its western border frames the foot of the Urals eastern ridges, and the eastern one adjoins the western limit of marine tertiary sediments of the West Siberian Plain. Igneous, sedimentary and metamorphic rocks of the Paleozoic prevail in geological structure, granite intrusions are widespread. Dominant soils are typical, southern and saline chernozem. The steppe zone forms latitudinal stripe of 2 degrees wide with its northern border along 54 10’ N. From the north to the south the climate becomes warmer and drier. A peculiarity of this area are numerous tiny pine, birch and aspen-birch forests forming a landscape of “false forest-steppe”. The article is based on the analysis of 286 geobotanical relevés made by authors in 2006–2021 in the southern part of Chelyabinsk Region. The classification was carried out using a modified TWINSPAN algorithm (Roleček et al., 2009) in the JUICE 7.0 package (Tichý, 2002). There are 7 associations, 1 subassociations, 5 variants and 1 community, belonging to orders Brachypodietalia pinnati (meadow steppes) and Helictotricho-Stipetalia (typical steppes) within the class Festuco-Brometea. Associations Artemisio nit­rosae–Festucetum valesiacae ass. nov. and Cari­ci supinae–Aizopsietum hybridae ass. nov., subass. ­Diantho aci­cularis–Orostachyetum spinosae inops subass. nov. and community Nepeta ucranica–Stipa lessingiana, as well as 5 variants were described for the first time. Ass. Diantho acicularis–Orosta­chyetum spinosae Schubert, Jäger et Mahn ex Yamalov, Zolotareva, Korolyuk, Makunina, Lebedeva ass. nov. and subass. Poo angustifoliae–Stipetum pennatae Yamalov, Bayanov, Muldashev et Averinova 2013 typicum subass. nov. were validated. Most of syntaxa forming the basis of steppe vegetation belong to the order Helictotricho-Stipetalia. The zonal herb-bunchgrass steppes of the ass. He­lictotricho desertorum–Stipetum rubentis occur on flat surfaces (placors) and gentle slopes, prevailing on hilly plain. Previuosly the such steppes dominated in the northern part of the steppe zone in the West Siberian Plain and Northern Kazakhstan, but now most of these have been replaced by arable land. The unplowed steppes which are strongly used as pastures now are assigned to the ass. Artemisio austriacae–Stipetum capillatae. Meadow steppes of the order Brachypodietalia pinnati are strictly related to the “false forest-steppe” landscape. In the steppe zone meadow steppes of the subass. P. a.–S. p. typicum (Fig. 4) occur at the edges of forests and in shallow depressions. Further north, in the forest-steppe zone of the Trans-Urals, this subassociation becomes typical. The mostly mesophytic meadow steppes of the “false forest-steppe” stripe belong to the subass. Galio veri–Stipetum tirsae serra­tuletosum coronatae. The main factors responsinle for differentiation of vegetation of the class Festuco-Brometea in study area are moisture, salinity and rock outcrops. The topological series along the moisture gradient is represented in the landscape of “false forest-steppe”: Galio veri–Stipetum tirsae serratuletosum coronatae (meadow steppes on the edges of forests) → Poo angustifoliae–Stipetum pennatae typicum (meadow steppes on the edges of forests and in shallow depressions) → Helictotricho desertorum–Stipetum rubentis (common herb-bunchgrass steppes). Numerous rock outcrops in the central part of the Urals are the reason for the wide distribution of pet­rophytic communities. However, the diversity and species richness of petrophytic steppes is small (only two associations) in the Trans-Urals peneplain where rough-skeletal and eroded soils are rare. Petrophytic steppes of the ass. Carici supinae–Aizopsietum hybridae ass. nov. (Table 11, rel. 1–12), holotypus: Table 11, rel. no. 4 (12-0173): Russian Federation, Chelyabinsk Region, Chesmenskiy district, mountain Shchukina near Kalinovskiy settlement, 53.81199° N, 60.50121° E, 12.06.2012, collector — A. Yu. Korolyuk) are common on granite outcrops in the most elevated relief elements of the Urals-Tobolsk watershed. Communities of the subass. Diantho acicularis–Orostachyetum spinosae inops subass. nov. (Table 10, rel. 1–12), holotypus: Table 10, rel. no. 11 (12-0139): Russian Federation, Chelyabinsk Region, Kartalinskiy district, right bank the river Karagaylyayat between the v. Varshavskay and Elizavethopolskoe, 52.81884° N, 60.45562° E, 09.06.2012, collector — A. Yu. Korolyuk) on the various rock outcrops are the impoverished variant of petrophytic steppes of the mountainous part of the Urals. The communities of the ass. Artemisio nitrosae–Festucetum valesiacae ass. nov. (Table 8, rel. 1–12. Holotypus hoc loco: Table 8, rel. no. 3 (12-0128): Russian Fede­ration, Chelyabinsk Region, Bredinskiy dist­rict, near Bredy settlement, 52.44794° N, 60.32095° E, 08.06.2012, collector — A. Yu. Korolyuk) occur on the slopes with saline tertiary clays in the eastern part of study area. The steppes of the Southern Trans-Urals combine the characteristic features of the steppe vegetation of adjacent territories. Herb-bunchgrass steppes in the Southern Trans-Urals are closely related to the West Siberian and Kazakhstan ones, while meadow steppes are associated with the Southern Urals syntaxa; the last ones include a number of European meadow-steppe species. There are some Urals endemics in syntaxa of petrophytic steppes, that make them closer to the Southern Urals syntaxa.