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The current state of the steppe vegetation classification system in the Volga region

Steppe vegetation in the Volga region is one of the predominant types of vegetation. At present, it has survived only in areas inconvenient for human economic and recreational activities. Its research is necessary to understand the structure and composition of zonal vegetation and distribution patterns to predict changes in the modern vegetation cover. The relevance of studying the steppe vegetation of the Volga region is also due to the creation of the project “Vegetation of Russia”. We studied the steppe vegetation of the Volga region in the period from 2011 to 2020 from the standpoint of the J. Braun-Blanquet approach. Field studies covered all the diversity of the steppe vegetation represented in the region-herb-rich grass steppes, herb-grass steppes, grass steppes and desert and their psammophytic, petrophytic and halophytic edaphic variants within Ulyanovsk, Penza, Samara, Saratov, and Volgograd Oblasts, the western part of Orenburg Oblast and the northern part of Astrakhan Oblast. The syntaxonomic analysis of our own materials and literature data made it possible to establish 65 associations, 47 subassociations and 2 variants. They are assigned to the class Festuco-Brometea, the orders Festucetalia valesiacae, Helictotricho-Stipetalia, Tanaceto achilleifolii-Stipetalia lessingianae and the alliances Festucion valesiacae, Agropyrion pectinati, Centaureion sumensis, Stipion korshinskyi and Tanaceto achilleifolii-Stipion lessingianae.


Introduction
The steppe vegetation in the Volga region is one of the predominant types of vegetation. However, at present, it has survived only in areas inconvenient for economic and recreational human activity. Its research is necessary to understand the structure and composition of zonal vegetation and the patterns of their distribution in order to predict changes in the modern vegetation cover. The relevance of studying steppe vegetation in a large region of Russia -the Volga region -is also due to the creation of the project "Vegetation of Russia" [1].
Our studies covered all the diversity of the represented in the region steppe vegetationherb-rich grass steppes, herb-grass steppes, grass steppes and desert and their psammophytic, petrophytic and halophytic edaphic variants within Ulyanovsk, Penza, Samara, Saratov, and Volgograd Oblasts, the western part of Orenburg Oblast and the northern part of Astrakhan Oblast.

Materials and Methods
We studied the steppe vegetation of the Volga region in the period from 2011 to 2020 from the standpoint of the approach by J. Braun-Blanquet [2]. 727 geobotanical relevés were made for the 25-100 m 2 sites using standard techniques [3]. The total grass projective cover was estimated as a percentage (%). The abundance scale by B.M. Mirkin was applied to assess the abundance of plant species on the survey sites [4]. The relevés were then introduced into a database "Vegetation of the Volga and Ural rivers basins" [5] developed on the basis of the TURBOVEG program [6] and processed using the JUICE program [7]. Syntaxonomic analysis was performed using the approach suggested by J. Braun-Blanquet [2].
The alliance Centaureion sumensis includes the continental relict stony steppes. The coenoses are described on the chalk slopes of the Privolzhskaya Upland (Stavropolsky District, Samara Oblast; Khvalynsky District, Saratov Oblast).

Conclusion
The modern syntaxonomical system of the steppe vegetation in the Volga region, one of the regions of Eurasia, in which the steppe type of vegetation prevails, currently numbers 123 units. It is prepared for inclusion in the classification system of vegetation in Russia [1] and international classifications of vegetation in Europe and Eurasia. Pre-allocated syntaxa will be included in the system after publication.