Aeolian forms of relief in the Orenburg Region occupy limited territories (Ryabukha, 2014). Sandy landforms in the region are distributed on terraces of the rivers Samara, Ural, Ilek, Irtek, Borovka, Bolshoy Uran, Malyy Uran, Or, Kumak, etc., and mostly are spread along the right banks of these rivers. They were formed generally as a result of redeposition of quaternary alluvial sands which average depth varies fr om 2 to 8 m. Two periods of degradation are known for sandy landscapes in the 1950–1960th (Gael, Smirnova, 1999; Chibilyov, Ryabukha, 2016). After the 1990th there was a decrease in a livestock that caused a decrease in the load on pastures and vegetation restoration. Currently, aeolian sands have local distribution and exist near settlements; the largest of them are noted at Burannoye, Izobilnoye, Novoiletskoyr, Kumakskoye, Linevka, etc.
Despite considerable number of publications devoted to steppes of the Orenburg Region (Chibilyov, 1996; Ryabinina, 2003; Chibilyov et al., 2004; Ryabukha, 2014; etc.), the psammophyte vegetation was poorly characterized (Ryabukha, 2013; Chibilyov, Ryabukha, 2016).
The aim of our study is to describe sandy steppe plant communities of the Orenburg Region and to define their syntaxonomical position. The paper is based on analysis of 122 releves performed in the course of the field studies in 2015–2016 at six areas in Sorochinsk, Tashly, Ilek, Akbulak and Sol-Iletsk districts of the Orenburg Region (Fig. 1–3).
The vegetation of sandy areas of the Orenburg Region was classified into 2 associations, 2 subassociations and 2 communities belonging to the class Festucetea vaginatae Soу ex Vicherek 1972, the order Festucetalia vaginatae Soу 1957 and the alliance Festucion beckeri Vicherek 1972 (Table 1). Among the species pool of the class Artemisia marschalliana, Carex colchica, Euphorbia seguieriana, Gypsophila paniculata, Helichrysum arenarium, Koeleria glauca, Kochia laniflora, Silene borysthenica (Fig. 5), Stipa borysthenica are registered with high constancy and often as dominants. The alliance is marked by four species with high constancy — Achillea micrantha, Festuca beckeri, Scorzonera ensifolia (Fig. 4), and Syrenia montana.
Ass. Asperulo diminutae–Festucetum beckeri ass. nov. hoc loco (Table 1, column 1; Table. 2, releves 1–34; nomenclature type (holotypus hoc loco)— releve 1 (Table 2): field releve number — 15–167, author — А. Yu. Korolyuk, coordinates: 52.56958° N, 53.08936° E, height 100 meters above sea level, 20/06/2015, Orenburg Region, Tashla district, 6km south from the village Kuzminka, the valley of the Irtek River, the bottom of blowing basins) represents communities of two sandy areas, isolated and remote from settlements, in valleys of the rivers Malyy Uran (Sorochinsk district) and Irtek (Tashla district). These communities occupy tops and slopes (4–30°) of low dunes, boards and the bottoms of blowing basins and the leveled interdune surfaces. Diagnostic species of association, such as Asperula diminuta, Centaurea sumensis, Tragopogon ruthenicus,are poorly resistant to a pasture regime.
Communities of ass. Helichryso arenarii–Achilleetum micranthae ass. nov. hoc loco (Table 1, column 2–3; Table 3, releves 1–29; nomenclature type (holotypus hoc loco) — releve 17 (Table 3): field releve— ml16–043, author — M. V. Lebedeva, coordinates: 51.39666° N, 53.62691° E, height 70 meters above sea level, 29/05/2016, Orenburg Region, Ilek district, 3.5 km southeast from the village Zatonnoye, the top of dune) are found in all sandy areas of the southern part of the Orenburg region (Tashly, Ilek, Sol-Iletsk and Akbulak districts). They occupy the leveled surfaces, tops and slopes (up to 8°) of dunes, the bottoms of blowing basins. Floristic composition includes groups of perennial (Achillea micrantha, Artemisia austriaca, Carex supina) and annual (Kochia laniflora, Poa bulbosa s. l., Polygonum aviculare agg., Secale sylvestre) species that are resistant to grazing. Their distribution is closely related with intensive pastures.
Subass. H. a.–A. m. typicum subass. nov. hoc loco (Table 1, column 3; Table 3, releves 13–29; nomenclature type (holotypus hoc loco) — releve 17 (Table 3)) represents the digressive variants of sandy steppes. In the southern part of the Orenburg Region (Ilek, Sol- Iletsk districts) they tend to occupy the leveled surfaces, tops and slopes of dunes as well as the bottoms of blowing basins.
Subass. H. a.–A. m.potentilletosumarenariae subass. nov. hoc loco (Table 1, column 2; Table 3, releves 1–12; nomenclature type (holotypus hoc loco) — releves 1 (Table 3): field releves — 16–027, author — А. Yu. Korolyuk, coordinates: 51.03627° N, 55.92618° E, height 170 meters above sea level, 27/05/016, Orenburg Region, Akbulak district, vicinity of the village Novoprivolnyy, a slope of gentle sandy ridge) is widely distributed in the valley of Ilek river (Akbulak and Sol-Iletsk districts). Coenoses occupy the leveled interdune surfaces, tops and slopes (to 5°) of flat dunes, the bottoms of blowing basins.
The community type Spiraea hypericifolia (Table 1, column 4; Table 3, releves 30–31) unites coenoses with well-developed shrub layer. They occur on sands only in Tashla district near the village of Kuzminka wh ere occupy the lowered sites of aeolian relief (the ravine and the bottom of blowing basins).
The community with dominance of Scirpoides holoschoenus (Table 1, column 5; Table 3, releves 32–33) form complexes with birch groves in little depressions that characterized by close bedding of ground waters.
Thus, there are clear patterns generated by pasture digression in psammophyte communities. With increasing of grazing, patterns of the prevailing life forms in the communities are changing: the cover of bunchgrasses (Festuca beckeri, Koeleria glauca, Stipa borysthenica) decrease, whereas species number and abundance of annual species (Chenopodium acuminatum, C. album, Lappula patula, Poa bulbosa s. l., Polygonum aviculare agg., Secale sylvestre) increase. The total cover of clonal plants increase, but without species number increasing. The overgrazing in sandy landscapes indicates by such species as Achillea micrantha, Artemisia austriaca, Carex supina, Secale sylvestre, Poa bulbosa s. l., Polygonum aviculare agg., and Kochia laniflora. It’s important to mention that under the increasing/reduction of deflation there are no concurrent increasing/reduction of a number of obligate psammophytes. Domination of obligate and facultative psammophytic bunchgrasses in plant communities demonstrates decrease of human impact during the last two decades, especially caused by reduction of a livestock.
Flora of toxic depots in selected industrial zones