Vegetation of chalk outcrops of Sub-Ural plateau and adjacent territories

The results of long-term studies of the vegetation of chalk outcrops of the Orenburg region (Russian Federation) and North-West Kazakhstan on Sub-Ural plateau and adjacent territories are presented. Chalk outcrops are unique botanical-geographical sites located in steppe and desert zones of Eurasia. Specific communities of calcephyte plant species have spread in these areas, in places of outcrops or close occurrence from the surface of upper-Cretaceous carbonate rocks. The flora of chalk outcrops is characterized by a great amount of rare species, mainly ende­mic, associated with peculiar substrates, the locality of habitats, and the historical past of the area of outcrops location (Matyshenko, 1985) The history of the study of flora and vegetation of chalk outcrops is given. Synthaxonomic studies of chalk vegetation as part of the ecological-floristic approach cover only territories west of the Volga river (Poluyanov, 2009; Averinova, 2011, 2016; Demina, 2014; Demina et al., 2016; Didukh et al., 2018). Chalk highlands of the North-West Kazakhstan and adjacent regions of the Russian Federation occupy quite large areas. However, up to date, there is no data on the vegetation diversity of these territories based on complete geobotanical relevés, that is why their synthaxonomy remains undeveloped. The study area with 15 massifs of chalk outcrops (Fig. 1) includes the Orenburg region (Novosergievsky, Perevolotsky, Sol-Iletskiy, Akbulak and Gaysky districts), and Aktobe (Hobdinsky, Uilsky and Bayganinsky district) and Atyrau (Zhylyoysky district) regions of the Republic of Kazakhstan. The largest massifs in the Orenburg region of the Russian Federation are: Starobelogorskie (Fig. 2), Chesnokov­skie (Fig. 3), Verkhnechibendinskie (Fig. 6), Troits­kie (Fig. 7), Pokrovskie Chalk Mountains (Fig. 4) and Durtel mountain (Fig. 5). Chalk massif Akshatau (Fig. 8) and the range Aktolagai (Fig. 9) are the largest within Aktobe region. The investigated sites are mostly located on the Sub-Ural Plateau, which extended from the southern regions of the Orenburg region to the Emba River in the territory of Aktobe region. They are less common within the Obschiy Syrt and sporadic in the Guberlinskie mountains. The study area covers a wide range of zonal vegetation from dry steppes in the northern part of the gradient to northern deserts in the southern one. The dataset includes 270 relevés of chalk outcrops communities performed by the authors in 2014–2019. The primary classification was carried out using TWINSPAN algorithm. As a result three groups of communities are established. The first group is communities of the Emben Plateau, the most southern area; second is communities on relatively developed soils in the slopes bases, depressions between chalk ridges and on their flat tops; third is widespread communities on most of the Podural Plateau and Obschy Syrt, excluding the Emben Plateau. Comparison with associations of calcephyte, semidesert and steppe vegetation (Golub, 1994; Kolomiychuk, Vynokurov, 2016; Lysenko, Yamalov, 2017; Didukh et al., 2018; Korolyuk, 2017) was made to determine the position of studied communities in the system of ecological-floristic classification of the herbasceous vegetation of Eurasia. Cluster analysis results (Fig. 10) revealed the significant specificity the chalk outcrops of the Sub-Ural Plateau in comparison with calciphytic communities of Eastern Europe, as well as with deserts and steppes zonal vegetation. That was the reason to describe a new class for vegetation of the studied chalk outcrops. The class Anabasietea cretaceae Golovanov class nov. hoc loco. Diagnostic species: Anabasis cretacea, Anthemis trotzkiana, Artemisia salsoloides, Atraphaxis decipiens,Crambe aspera, Echinops meyeri, Jurinea kirghisorum, Hedysarum tscherkassovae, Lepidium meyeri, Limonium cretaceum, Linaria cretacea, Matthiola fragrans, Nanophyton erinaceum, Seseli glabratum, Zygophyllum pinnatum;holotypus is order Anabasie­talia cretaceae ord. nov. hoc loco. Class combines calciphytic, mainly semi-shrub communities on the outcrops of chalk and marl rocks of the south of the Orenburg region and North-West Kazakhstan within the steppe (subzones of the true and desert steppes) and desert zone. The central order, Anabasietalia cretaceae Golovanov ord. nov. hoc loco, is described;holotypus is alliance Anthemido trotzkianae–Artemision salsoloidis all. nov. hoc loco. Three alliances identified within the order reflect both community distribution along the latitudinal gradient and succession stages. The alliance Sileno fruticulosae–Nanophytonion erinacei Lebedeva all. nov hoc loco is poor-species communities, located mainly on the chalk massifs in the southern part of the Sub-Ural Plateau (Emben Plateau) and adjacent territories. Holotypus of the alliance is ass. Onosmo staminei–Anabasietum cretaceae ass. nov. hoc loco with highly constant desert plant species (Anabasis salsa, Artemisia terrae-albae, Atriplex cana, Limonium suffruticosum, Rhammatophyllum pachyrhizum, etc.). It includes the ass. Onos­mo staminei–Anabasietum cretaceae ass. nov. hoc loco (Table 3, syntaxa 1–3; Tables 4–6). Holotypus hoc loco: Table 4, rel. no. 9 (YS19-034): Republic of Kazakhstan, Atyrau region, Zhylyojskij district, 10 km W Aktologay ridge, 47.48514° N, 54.97647° E, 19.05.2019, collector Yamalov S. M.) The alliance Anabasio cretaceae–Agropyrion desertorum Korolyuk all. nov hoc loco.Holotypus is ass. Agropyro desertorum–Artemisietum lessingianae ass. nov. hoc loco. Alliance includes communities in flat habitats with well-developed soils at the foot of the chalk hills in the central and northern parts of the Sub-Ural Plateau, on the chalk rock outflows, as well on their tops. Active are species of deserts and galophytic communities of the classes Artemisietea lerchianae and Festuco-Puccinellietea, as well as these of dry and desert steppes of the order Tanaceto achilleifolii–Stipetalia lessingianae. There are 2 associations: Agropyro desertorum–Artemisietum lessingianae ass. nov. hoc loco (Table 3, syntaxon 4; Table 7; fig. 23; holotypus hoc loco: Table 7, rel. no 8 (YS15-019)), Russian Federation, Orenburg region, Sol-Ilets­kiy district, Troitsk Chalk Mountains, 10 km SW vil. Troitsk, 50.65317° N, 54.542° W, 06.06.2015, collector Yamalov S. M.) and Psephello marschallianae–Artemisietum lerchianae ass. nov. hoc loco ((Table. 3, syntaxon 5; Table 8; fig. 24); holotypus hoc loco: Table 8, rel. no 15 (YS19-050), Republic of Kazakhstan, Aktyubinsk region, Hobdinsky district, chalk mountains 16 km NE vil. Zhantalap, 50.39986° N, 56.05054° N, 21.05.2019, collector Yamalov S. M.). The alliance Anthemido trotzkianae–Artemision salsoloidis Yamalov all. nov hoc loco.Holotypus is ass. Anthemido trotzkianae–Artemisietum salsoloi­dis ass. nov. Alliance includes the cenoses of the chalk highlands of the Sub-Ural Plateau (except for its extremely southern part) and the Obschiy Syrt. These are both communities of the initial and more advanced succession stages. The high constancy of Anthemis trotzkiana and Artemisia salsoloides, as well as the presence of petrophytic species widely distributed in the rocky steppes of the Southern Ural (Alyssum tortuosum, Centaurea marchalliana, Euphorbia seguieriana, Galium octonarium) are character for the alliance cenophlora. There are three associations— Nanophytono erinacei–Jurinetum kirghisori ass. nov. hoc loco (Table 3, syntaxon 6; Table 9; Fig. 25; holotypus hoc loco: Table 9, rel. no 7 (GY18-070)), Russian Federation, Orenburg region, Sol-Iletskiy district, Verhnechibendinskie Chalk Mountains, 10 km W vil. Troitsk, 50.6562° N, 54.44272° W, 07.06.2016, collector Golovanov Ya. M.); Anthemido trotzkianae–Artemisietum salsoloidis ass. nov. hoc loco (Table 3, syntaxa 7, 8; Tables 10, 11; Fig. 26; holotypus hoc loco: Table 10, rel. no 20 (GY15-047)), Russian Federation, Orenburg region, Sol-Iletskiy district, Troitsk Chalk Mountains, 10 km NW vil. Troitsk, 50.65267° N, 54.54217° E, 06.06.2015, collector Golovanov Ya. M.); Onosmo simplicissimae–Anthemietum trotzkianae ass. nov. hoc loco (Table 3, syntaxon 9; tab. 12; Fig. 27); holotypus hoc loco: Table 12, rel. no 1 (GY19-011)), Republic of Kazakhstan, Aktyubinsk region, Uilskii district, Terektytau, 10 km NE vil. Akshatau, 49.43507° N, 54.60127° E, 15.05.2019, collector — Golovanov Ya. M.). There are 2 associations in the class Festuco-Brometea. Within the dry steppe order Tanaceto achilleifolii–Stipetalia lessingianae this is Bassio prostratae–Agropyretum desertorum ass. nov. hoc loco (Table 3, syntaxa 10, 11; Table 13), holotypus hoc loco: Table 13, rel. no 8 (GY19-004)), Republic of Kazakhstan, Aktyubinsk region, Uilskii district, Terektytau, 10 km NE vil. Akshatau, 49.42942° N, 54.60047° E, 15.05.2019, collector Golovanov Ya. M.); within the true steppe order Helictotricho-Stipetalia this isass. Anthemido trotzkianae–Thymetum guberlinensis ass. nov. hoc loco (Table 3, syntaxon 12; Table 14); holotypus hoc loco: Table 14, rel. no 8 (GY14-012)), Russian Federation, Orenburg region, Gayskii district, chalk mountain Dyurtel, 4 km NE vil. Starohalilovo, 51.504° N, 58.157° E, 27.06.2014, collector Golovanov Ya. M.). The result of the research of chalk outcrops ve­getation of Sub-Ural plateau and adjacent territories is new class Anabasietea cretaceae which includes 1 order, 3 alliances, 6 associations, 3 subassociations, 2 variants and 9 facies.