Сommunities of xerotheme shrubs of South Urals

Communities of shrubs such as Prunus fruticosa, Spiraea crenata, S. hypericifolia, Caragana frutex (Lavrenko, 2000) are widespread in the Eurasian steppe region. Currently, science has a special interest in the study of shrub communities and some species of shrubs due to their expansion into grass ecosystems. So, there is an increasing of the communities areas, their range in the forest-steppe and steppe zones as a result of sharp decrease in livestock after the economic reforms of the 1990s in the Russian Federation. In the syntaxonomic literature, the steppe shrub communities are included in the class Crataego-Prunetea Tüxen 1962 nom. conserve. proposal. (Mucina et al., 2016). Xerothermic shrub steppe communities are placed in the alliance Amygdalion nanae Golub 2011, the order Festucetalia valesiacae Korneck 1974 nom. conserve. proposal. and the class Festuco-Brometea (Yamalov et al., 2012). The study and classification of shrubby vegetation in South Ural (SU) has so far been represented by few works.The development of the syntonomy of shrubby communities on the base of ecological and floristic classification has got started with the paper of German geobotanists who selectively examined the steppes of some areas of the Bashkir Urals and Trans-Urals (Schubert et al. 1981). The study of steppe shrubby communities by Ufa geobotanists was carried out mainly during the inspection of protected areas. Communities were studied on the Shaitan-tau ridge (Dubravnaya forest-steppe..., 1994), in the Bashkiria National Park (Yamalov, Sultangareeva, 2010), on the territory of natural monuments — Tratau and Yuraktau mounains (Unique..., 2014), in the Bashkir State Reserve (Yamalov, 2011). The study was carried out at South Ural within the Republic of Bashkortostan, as well as in the adjacent territories of the Orenburg and Chelyabinsk regions. The length of the studied area from north to south is about 550 km, from west to east — about 400 km. The work is based on 147 geobotanical relevés of xerothermic shrubby communities, made from 1981 to 2015. Both author’s relevés and published data included in the “Database of non-forest vegetation of South Ural” GIVD id 00-RU-006 (Yamalov et al., 2012) were used for the syntaxonomic analysis. The dataset was processed using the JUICE program (Tichý, 2002). The characterizing tables contain data of the species presence in projective cover scores on the following scale: + < 1 %, 1 — 1–4 %, 2 — 5–9 %, 3 — 10–24 %, 4 — 25–49 %, 5 — 50–74 %, 6 — 75–100 %. The nomenclature of syntaxa follows the rules of the International Code of Phytosociological Nomenclature (Theurillat et al., 2021). The names and diagnostic species groups of high-rank vegetation units are as in “Vegetation of Europe...” (Mucina et al., 2016) with regional adjustments. Species names are given by Plants of the World Online (https://powo.science.kew.org/), as well as by taxonomic treatments in the flora of South Ural (Ryabinina, Knayzev, 2009). Based on the results of syntaxonomic analysis, it is proposed to consider it as part of two classes Festuco-Brometea and Crataego-Prunetea. A comparative analysis of the xerothermic shrubby vegetation syntaxa of the alliance Prunion fruticosae in Eastern Europe demonstrated that the communities of South Ural due to significant specificity, might be considered within the framework of the sub-alliance Carici supinae–Spiraenion crenatae. One of the leading factors of such differentiation is mainly the climatic features of the region located in the zone of temperate continental climate. There is a genesis and spatial relationship between shrub communities and broad-leaved forests of the Carpino-Fagetea class, with hemiboreal forests of the class Brachypodio pinnati–Betuletea pendulae, as well as steppes of the class Festuco-Brometea. We assume that the communities of the sub-alliance Carici supinae–Spireanion crenatae represent the eastern limit of the range of the class Crataego-Prunetea. There are Artemisia armeniaca, Artemisia sericea, Carex supina, Cotoneaster melanocarpus, Dianthus chinensis, Dracocephalum ruyschiana, Dracocephalum thymiflorum, Echinops ruthenicus, Eremogone longifolia, Koenigia alpina, Onosma simplicissima, Pentanema hirtum, Poa versicolor, Rhaponticoides ruthenica, Sanguisorba officinalis, Salvia stepposa, Spiraea crenata, Stellaria graminea, Thymus pannonicus, Veronica spuria in diagnostic group of sub-alliance. The suballiance includes 3 associations with the dominance or codominance of different shrubs, as well as 10 subassociations reflecting the edaphic conditions of specific habitats, as well as their geographical differentiation. The communities of two associations, characterized by the lot of steppe species in the grass layer, are classified as part of the alliance Amygdalion nanae. The most xerothermic communities of the ass. Artemisio austriacae–Spiraetum hypericifolii with the Spiraea hypericifolia dominance have become widespread at the southern tip of the Urals (Guberlinskye Mountains) and the Trans-Urals small hill. In the northeast of the Trans-Urals, along the mountain slopes, mainly western and northwestern exposures with slopes from 10 to 45°, shrubby communities of the ass. Phedimo hybridi–Cotoneasteretum melanocarpi are common on rocky substrates. Shrubby communities with Prunus tenella prevalence (ass. Filipendulo vulgaris–Prunetum tenellae) are widespread in forest-steppe and steppe zones of the Cis-Urals and a mountain part of South Ural on slope habitats of various exposures, with biases from 3 to 40° on stony limy substrates, and on the flattened relief elements on forest margins. The most common type of shrub communities in the region is the thickets of Caragana frutex of the ass. Fragario viridis–Caraganetum fruticis. They are formed within the forest-steppe and steppe zones, both on slopes of various exposures along beams, ravines, and forest margins on flattened relief elements. The most diverse in the South Ural are shrubby communities of the ass. Trifolio montani–Prunetum fruticosae, which combines cenoses with the Prunus fruticosa dominance. Communities are formed on various exposition slopes along ridges, beams, ravines, thermophilic forest margins, and on flattened relief elements; often on rocky substrates. Among all xerothermic shrubs, only Spiraea crenata does not form an independent syntaxon. However, the species noted as constant in many associations, often coexist with coenosis-forming shrubs.