Labor consumption of phytomass measurements on sample plots hinders the extrapolation of point data to areas comparable to commercial lands or landscape units. Vegetation indices calculated from satellite images are usually considered indicators of green phytomass; they are used for its areal estimates. The task of this study is to establish the informativity of the normalized differential vegetation index (NDVI) depending on the fractional structure of living and dead aboveground phytomass, seasonal dynamics of the biological cycle, hydrothermal conditions, and landscape position. The results of monthly measurements of aboveground phytomass fractions on 13 sites in phytocenoses of forest feather grass and feather grass formations in the Burtinskaya steppe (Orenburg Nature Reserve) from May to September 2015–2020 were used. The NDVI values were calculated for each period from Landsat satellite images at all sites. Hypotheses about geobotanical, hydrothermal, phonological, and landscape factors of NDVI informativity were tested by calculating the Spearman correlation coefficients using the dispersion and multiregression analysis. The discrepancy between the seasonal peaks of the NDVI and green phytomass is not consistent with the common concept of a direct indicator value of the NDVI. The total live biomass correlates more clearly with the index in June and July; the correlation is lower in the end of the season. The NDVI index turned out to be sensitive not so much to the reserves of green phytomass, but more to the mass and proportion of forbs and the ratio of live and dead phytomass. In late spring and early summer, the NDVI is most closely associated with forbs and, in July, with cereals. The hypothesis about the possibility of screening green mass with standing dead biomass was confirmed, which leads to a decrease in the NDVI despite the preservation or growth of green phytomass. The NDVI may underestimate the real green phytomass if there is a sharp increase in the mass of standing dead biomass, usually in the second half of summer and early autumn. The NDVI more adequately reflects the state of the aboveground phytomass of steppe communities that have not been exposed to fires for a long time when compared with burned communities and fallows.

Аннотация.Влияние пожара на химический состав надземной фитомассы степей изучалось в 2015-2016 гг.на территории участка «Буртинская степь» ГПЗ «Оренбургский».В статье приведены данные по содержанию некоторых органических веществ в живой надземной фитомассе разнотравно-типчаково-ковылкового сообщества с Artemisia marschalliana -одного из распространенных типов сообществ на данной территории.Прослежена динамика накопления основных химических веществ в надземной фитомассе на контрольных и сгоревших площадках: сырой протеин, сырая клетчатка, сырой жир, углеводы (сахар, крахмал)

In recent years, in the arid regions of Russia, there has been a catastrophic increase in the area and frequency of fires in the steppes. At the same time, the entire above-ground part of phytocenoses burns out, which significantly reduces the reserves of the live above-ground phytomass, the productivity of communities, and changes the structure and composition of steppe phytocenoses. The purpose of our work was to study the effect of the pyrogenic factor on the stocks of the live aboveground phytomass and determine the timing of its recovery. In the Burtinskaya Steppe area of the Orenburgsky State Nature Reserve six monitoring sites were laid in 2015 after a fire, each included a control (unburnt) site and a burnt site. To identify the features of the dynamics of the stocks of live aboveground phytomass, standard geobotanical methods and the method of cutting areas were used. The studies were carried out in the 2015–2020 period. As a result of studying the effect of the pyrogenic factor on the vegetation cover of the steppes, it was found that the reserves of live aboveground phytomass (g/m 2 ) reach the value of the control communities in the second year of the study. The seasonal dynamics of live phytomass stocks from 3–4 years after the fire depends more on the composition and type of the community and not on whether it was exposed to a pyrogenic factor. Over the entire period of the study the share of live phytomass reserves in the total aboveground phytomass of burned communities approached the values of control phytocenoses; however, there was always more in the control, which indicates incomplete restoration of the structure of the aboveground phytomass in the burnt areas.

The map of the current vegetation on the territory of the present and expected distribution of the Saiga population in the North-Western Caspian region is presented. The map was created due the research work under an agreement of the World Wide Fund for Nature (WWF) at a scale of 1 : 200,000 in the ArcGIS. The legend contains 61 numbers, which are combined into 11 groups according to the dominant formation. In the steppe zone fallow lands and pasture fields of different ages on slightly undulating and undulating plains with light chestnut soils (Kastanozem by WRB) are represented by Stipa sareptana, Artemisia lerchiana communities on loamy and sandy loam soils in complexes with Artemisia lerchiana and Leymus ramosus, Poa bulbosa, Agropyron desertorum communites on solonetzes (I); Stipa sareptana, S. lessingiana, Festuca valesiaca, Agropyron desertorum, Poa bulbosa, Artemisia lerchiana, Tanacetum achilleifolium communities on loamy and sandy loam soils in complexes with Artemisia lerchiana, A. pauciflora, Tanacetum achilleifolium communites on solonetzes (II); Festuca valesiaca, Agropyron desertorum, Stipa sareptana, Leymus ramosus, Artemisia lerchiana communities on loamy and sandy loam saline soils in complexes with Artemisia lerchiana, A. pauciflora, Tanacetum achilleifolium, Poa bulbosa, Leymus ramosus communites on solonetzes (III); Poa bulbosa, Agropyron desertorum, Stipa sareptana, Leymus ramosus, Artemisia lerchiana, A. taurica, Tanacetum achilleifolium communities on loamy and sandy loam saline soils in complexes with Artemisia taurica, A. lerchiana, A. pauciflora communites on solonetzes (IV); Artemisia lerchiana, A. austriaca, Festuca valesiaca, Agropyron desertorum, Leymus ramosus and Festuca valesiaca, Poa bulbosa, Artemisia austriaca communities on loamy and sandy loam saline soils in complexes with Artemisia pauciflora, A. santonica communites on solonetzes (V). In the desert zone pasture fields on hilly sands, on undulating plains with brown desert (Calcisol by WRB) sandy and sandy loam soils are represented by Artemisia lerchiana, Poa bulbosa and Poa bulbosa, Artemisia lerchiana communities (VI); Artemisia lerchiana, Poa bulbosa and Poa bulbosa, Artemisia lerchiana communities on brown desert saline soils of light granulometric composition in complexes with Artemisia pauciflora, Poa bulbosa communites on solonetzes (VII); complexes of Artemisia lerchiana, Poa bulbosa and Artemisia taurica, Poa bulbosa communities on brown desert saline soils of light granulometric composition (VIII); complexes of Poa bulbosa, Artemisia lerchiana and Poa bulbosa, Artemisia taurica communities on brown desert saline soils of light granulometric composition (IX); Artemisia lerchiana, Poa bulbosa communities on undulating and wavy sands, Calligonum aphyllum on hilly sands (X); Poa bulbosa, Stipa sareptana, S. caspia, Agropyron fragile, Sporobolus cryptandrus, annual ( Ceratocarpus arenarius , etc.) communities on intensive pastures with brown desert sandy soils (XI).

We carried our investigationsin one of the typical phytocenosesof the Trans-Volga-Kazakhstan herb bunchgrass steppes underprotected regime conditions. Forb-fescue-feather grass steppe community (Stipa zalesskii, S. lessingiana, Herbae stepposae) with Helictotrichon desertorum (Less.) Nevski and petrophytous elementswere considered as a model. The dynamics of the above-ground phytomass stocks of this community was on the “Burtinskaya steppe” site in the Orenburg State Nature Reserve using thesquare sample cut method. The content of the main macroelements N, K, Na, Ca, P, and Mg is determined. The Federal State Budgetary Institution and the State Agrochemical Service Center “Orenburgsky” conducted the analysis of the plant samples.The resultsobtained were compared with the available literary data. Statistical analysis using the nonparametric Mann-Whitney U-test (α=0.05) in Statistica 6.1 revealed significant differences in the content of some macroelements between the drought year 2015 and the wet year 2016. The share of cereals (dominant community Stipa zalesskii Wilensky, codominant S. lessingiana Trin. & Rupr.), both in living above-ground phytomass and in dead grass, have been prevailing. The following series of accumulation of elements: N>K>Na>Ca>P>Mg was common for both fractures in most reference periods. The above-ground phytomass stocks in the examined community ranged from 335 g/m² to 404 g/m² in 2015 and from 525 g/m² to 678 g/m² in 2016. The findings obtained complement the available data for grasslands and pastures, present the opportunity to assess them comparatively with reference to standard and steppe zones, and serve as the foundation for further monitoring.

The article reports the first finding of Hammarbya paludosa (L.) Kuntze in the Orenburg Region. The species was found in 2014 in the “Buzulukskiy Bor” National Park, in location called “Losinaya Pristan”, which represents a refuge for many extremely rare in the Orenburg Region boreal plants. This orchid was earlier mistakenly determined as Herminium monorchis (L.) R. Br. We recommend to include Hammarbya paludosa in the Red List of the Orenburg Region.

The aim of this work was to identify and analyze the ontogenetic and spatial structure of steppe plant Clausia aprica (Stephan) Korn.-Tr. (Brassicaceae) cenopopulations at the border of distribution. The study of cenopopulations and their habitat conditions was conducted at 2006–2021 in Samara, Volgograd, and Orenburg Oblasts (Russian Federation). For the first time determined the polyvariance of development of individuals, the duration of ontogenetic stages and complete ontogenesis, peculiarities of spatial location and evaluation of running window methods. A table of prohibitions and resolutions of transitions between ontogenetic states was compiled for C. aprica ontogenesis. It was found that permissions of transitions between ontogenetic states are 37.8%. In natural cenopopulations, mutual transitions of individuals from one ontogenetic state to another has adaptive significance and determines the dynamics of the ontogenetic structure. At intervals of 6-8 years, a slight increase in the number of C. aprica individuals is observed in the populations, which is ensured by the efficiency of seed reproduction. Thus, self-maintenance and self-renewal of species populations is possible in case of low level of anthropogenic impact on vegetation cover of territories.