Ecological and phytocenotic characteristics of plant communities of Nitraria schoberi L. in Dagestan

For the first time, an ecological-phytocenotic classification of communities of Nitraria schoberi L., widespread in the territory of the Republic of Dagestan has been developed. 29 geobotanical descriptions were carried out on sample plots (SP) taking into account the floristic composition, as a result of which 7 formations, 14 groups of associations and 27 associations were identified. In the course of research, 179 species of higher vascular plants were identified in communities with the participation of Nitraria schoberi. The largest was the Nitrarieta schoberi formation with 7 groups of associations and 14 associations, in which 128 species of vascular plants grow.


Introduction
Increased unsystematic use of natural resources, disturbance of the condition of pastures and other negative factors contribute to the emergence of many environmental problems, in particular the process of desertification.
In this regard, it became necessary to study communities with the participation of the Red Data Book species Nitraria schoberi in Dagestan, one of the few fruits and berry plants capable of growing on salt marshes and well tolerating being covered with sand, which is a natural sand-strengthening agent. Modern studies on the study of communities with the participation of Nitraria schoberi are given in works E.V. Mavrodiev et all., I.A. Rukhlenko, E.V. Banaev et all., I.A. Goryaev [1][2][3][4][5][6].

Methods
The work used materials and collections of field research carried out in 2015-2018. as part of expeditions. In communities with the participation of Nitraria schoberi, test plots of 20 × 20 m were laid. The test plots were tied to a geographic grid using a personal GPS radio navigator. The names of syntaxa are given in accordance with the Code of phytosociological Nomenclature [7].

Formation Nitrarieta schoberi
Nitraria schoberi L. -halophytic shrub, xerophyte. The range of the species Nitraria schoberi L. is mainly made up of the Caspian and Turan lowlands, where saltpeter is found in large quantities. In the north, its distribution is limited by the line: 56 ° N (Omsk); in the west, it is known in Ergeny, on the territory adjacent to the Caspian Sea. Also, in the west are its severed locations in the eastern Crimea near Sudak, as well as in the Lower Danube lowland. The distribution area of Nitraria schoberi (according to literature data) is the Caucasus, Central Asia, Western Siberia, Iran and Western China [12][13][14][15]. There is an indication of the growth of Nitraria schoberi in the Ploiesti region of Romania in the "Flora of Romania" [16]. Its range covers the entire Ordos, the Alashan Desert, partly the Mongolian Gobbi, the foothills and low mountains of the Nan Shan and Altyn Taga, the eastern outskirts of the Tsaidam Basin with the surrounding foothill plains [17,18]. In the east it reaches the regions of Kashgar and Dzungaria. In the south, the range of N. schoberi reaches Afghanistan; so far only one locality is known (Khusan on Gerirud) [19]. The total projective cover in Nitraria schoberi in the shrub layer varies from 5 to 50%, and in the herbaceous layer from 10 to 45%.
The species composition of the communities of the Nitraria schoberi includes 129 species of higher vascular plants. In communities, species of the genus Tamarix often codominated. With saline soils, hyperhalophytes of Halimione verrucifera are abundant in them, less often Halocnemum strobilaceum and Nitraria schoberi.
Based on our own descriptions, we carried out an ecological-phytocenotic classification of communities of the Nitrarietae schoberi formation, widespread in the Republic of Dagestan. It includes 6 groups of associations and 14 associations.

Group of associations Artemisieta tschernievianae
The group of associations Artemisieta tschernievianae is rare, on the sandy ridges of the coastal lowland. The projective cover of the shrub layer is about 40%, of the herbaceous layer up to 25%.

Group of associations Botriochleta ischaemae
The group of associations Botriochleta ischaemae occurs on the rock taluses of Inter Mountain Dagestan. The projective cover of the shrub layer is 10%, herbaceous layer is about 30%.
Along with Nitraria schoberi, in the communities of this class of associations, the background species of the shrub layer are Clematis orientalis, Tamarix

Group of associations Botriochleta ischaemae-herbosae
Communities of the Botriochleta ischaemae-herbosae group of associations are found near saline lakes, hydrogen sulfide springs and depressions in the coastal part of the Primorskaya plain of Dagestan, on salt licks. The projective cover of the shrub layer varies from 25 to 50%, and of the grass layer 20-30%.
In the ravines of a temporary watercourse on the coastal part, the role of the background species, along with Nitraria schoberi, is assumed by Elaeagnus angustifolia, and at the outcrops of limestone plates, Rhamnus pallasii. The main dominants of the herbaceous layer are xero-holophytic perennials Artemisia santonica, A. annua, Limonium mejeri, Plantago scabra, Galium aparine, Teucrium polium, and Eryngium caucasicum.

Group of associations Artemisieta lerchianae
The group of associations Artemisieta lerchianae are found near salt lakes, in depressions of the Caspian lowland with a high groundwater table, on sands. The projective cover of the shrub layer is from 10 to 40%, and of the herbaceous layer 15-45%.
In the group of associations Artemisieta lerchianae, the background species of the shrub layer is Nitraria schoberi in rare cases, Rhamnus pallasii can be a together dominates. In the grass layer, the role of dominants in the communities located near salt lakes is assumed not only by Artemisia lercheana, but also by Plantago lanceolata, Galium aparine, Artemisia austriaca, Botriochloa ischaemum, and in the depressions of the Caspian lowland Anizantha rubens and Poa bulbosa. The constant species of this class of associations are Artemisia lercheana, Agropyron pectinatum, Medicago caerulea, Asparagus officinalis.

Group of associations Artemisieta marshallianae
Communities of the group of associations Artemiseta marshallianae are more often found on dry slopes with outcrops of salts, in ravines with a temporary watercourse. The projective cover of the shrub layer is from 5 to 12%, and of the herbaceous layer is 10-25%.
In the shrub layer of this of associations, the main dominant is Nitraria schoberi, in rare cases, Clematis orientalis. The main feature of the herbaceous layer is the occurrence of tap-root perennial plants Convolvulus arvensis, Artemisia marshalliana, Parietaria judaica, Gypsophila capitata, Erysimum meyerianum, Euphorbia virgata. Among cereals, Botriochloa ischaemum is a codominant.

Group of associations Artemisieta santonicae -nitrarieta schoberae
Communities of the group of associations Artemisieta santonicae -nitrarieta are rare, near saline lakes and depressions on salt licks. The projective cover of the shrub layer is up to 35%, and that of the herbaceous layer is up to 20%.
The background species of the shrub layer is Nitraria schoberi, and Teucrium chamaedrys, Eryngium caucasicum, and Centaurea squarrosa dominate in the herbaceous layer along with Artemisia santonica. Among cereals Botriochloa ischaemum and Bromus briziformis are together dominates.

Formation Artemisieta austriacae
Artemisia austriaca Jacq. -halophyte, with a creeping adventitious root system. The range of the species stretches from the territory of the Caucasus, Central Asia, Iran, Ukraine, Moldova, Crimea, Belarus to Northwest China. For the growth of Artemisia austriaca prefers old fallow lands, forest-steppe and steppe zones, alkaline meadows, pastures, steppe and steppe slopes.
The total projective cover in the communities of the Artemisia austriaca and in the shrub and grass layers reaches 40%.
The species composition of the Artemisia austriaca communities is very poor and includes up to 10 species of higher vascular plants. This is due to the fact that the soil is subject to water and wind erosion, so ephemeroids and annuals do not take root.
In these communities, the main place is occupied by the species Artemisia austriaca and Carex humilis, and among the shrubs Nitraria schoberi, Colutea orientalis, and Salsola daghestanica.
Based on our descriptions, an ecological-phytocenotical classification of communities of the Artemisietae austriacae formation, widespread in the Republic of Dagestan, was carried out. It includes 1 group of associations and 1 association.

Group of associations Artemisieta austriacae-fruticosa
Communities of the Artemiseta austriacae-fruticosa group of associations occur on dry slopes with loose shale, subject to constant water and wind erosion. The projective cover both in the shrub and grass layers reaches 40%. Colutea orientalis and Salsola daghestanica are the background species of the shrub layer, together with Nitraria schoberi; in the herbaceous layer Carex humilis codominates with Artemisia austriaca.

Formation Artemisieta tauricae
Artemisiа taurica Willd. -a perennial plant with a rod thick, upright, woody root system. Occurs from Crimea in the west to the Bogdinsko-Baskunchaksky nature reserve in the Astrakhan region in the east. On the territory of the range, Artemisiа taurica is distributed intermittently, and it is classified as a rare plant. However, at present, this Artemisiа taurica is expanding its range, actively spreading over fallows in the south of the steppe zone and in the desert zone [20].
The total projective cover in communities of Artemisiа taurica in the shrub layer varies from 8 to 40%, and in the herbaceous layer from 20 to 50%.
The Artemisiа taurica communities are rich in species composition, including 59 species of higher vascular plants. The  Based on the results of our own descriptions, we carried out an ecologicalphytocenotical classification of communities of the Artemisietae tauricae formation widespread in the Republic of Dagestan, which includes 2 groups of associations and 6 associations.

Group of associations Artemisieta tauricae-fruticosa
Communities of the group of associations Artemisieta tauricae-fruticosa occur on dry slopes with loose shale, subject to constant water and wind erosion in the ravines of a temporary watercourse. The projective cover of shrub and grass layers reaches 40%.
In the group of associations Artemisieta tauricae-fruticosa, the background species of the shrub layer is Nitraria schoberi, Spiraea hypericifolia, Colutea orientalis, Salsola ericoides, Salsola daghestanica. Rhamnus pallasii and Cerasus incana are also found. In the herbaceous layer, Artemisia taurica is the main dominant species. Medicago caerulea, Iris timofejewii, and Artemisia salsoloides are often found in such communities.

Group of associations Artemisieta tauricae
The group of associations Artemisieta tauricae is found on heavily eroded shale slopes in the ravines of a temporary watercourse, as well as on salt marshes with a salt crust, on the shores of salt lakes. The projective cover of the shrub layer is from 8 to 20% and of the herbaceous layer is from 20 to 50%.
In the Artemisieta tauricae group of associations, the background species of the shrub layer are Nitraria schoberi and Tamarix ramosissima. Tamarix laxa, Atraphaxis daghestanica are rare.
In the herbaceous layer, the dominant communities of this class of associations located on the shale slopes in the ravines of the temporary watercourse are played by the species Medicago caerulea, Convolvulus arvensis, Capparis herbacea, and Artemisia marshalliana. The communities of the class of associations Artemisieta tauricae located along the shores of salt lakes are dominated not only by Artemisia taurica, but also by Noaea mucronata, Halimione verrucifera, Carex distans, Calamagrostis caucasica, Phleum phleoides.

Formation Artemisieta santonicae
Artemisia santonica L. is a halophytic perennial plant with a rod-and-root system. The range of the species is the Black Sea-Northwest Caspian, it stretches from the Black Sea region (33º E) in the west, to North-Western Kazakhstan (45º E) in the east. The northern border reaches 52º N, the southern one -44º N. [21]. Artemisia santonica is a desert-steppe species [22,23].
The projective cover of the shrub layer is up to 10%, of the grass layer is 30%. The species composition community of the Artemisia santonica is scanty (10 species of higher vascular plants). The communities are often dominated by shrubs of Nitraria schoberi and species of the genus Tamarix. In the herbaceous layer, the main role is played by Artemisia santonica, Noaea mucronata, Halimione verrucifera.
Based on the results of our own descriptions, we carried out an ecologicalphytocenotical classification of communities of the Artemisieta santonicae formation, widespread in the Republic of Dagestan, which includes 1 group of associations and 1 association.

Group of associations Artemisieta santonicae
Communities of the Artemisieta santonicae group of associations are found on salt marshes along the shores of salt lakes of the coastal plain. The projective cover of the shrub layer reaches 10%, of the herbaceous layer 30%.
The background species of the shrub layer is Nitraria schoberi and Tamarix ramosissima, rarely Salsola glauka. The main dominants in the communities of the group of associations Artemisieta santonicae are Artemisia santonica, Noaea mucronata. These communities also contain Artemisia taurica, Alhagi pseudalhagi, Gypsophila paniculata, and one of the hyperhalophytes, Halimione verrucifera, is often found.

Formation Tamariсeta laxae
Tamarix laxa Willd. -a large, highly branched shrub or in the form of a small tree up to 5 m tall. Grows in the lower reaches of the Volga, Central Asia, Mongolia, Northwest China, Northern Iran, Afghanistan. In Dagestan, it grows on the Terek-Sulak lowland to the lower mountain belt [7]. It is very unpretentious to soil conditions, tolerates salinity well, and is insensitive to drought. It is used in single and group plantings as an ornamental and sandfixing plant in the south and southeast of the European part of Russia.
The projective cover of the shrub layer varies from 10 to 35%, and of the herbaceous layer from 25 to 55%.
The species composition of the communities of this formation includes 40 species of higher vascular plants. The communities are often dominated by shrubs of Nitraria schoberi and species of the genus Tamarix laxa. In the herbaceous layer, the main role is played by Artemisia taurica, Medicago caerulea, Medicago minima, Leymus racemosus, Poa bulbosa, Hordeum leporinum, Silene conica, Aira notarisiana, Carduus cinerus.
Based on the results of our own descriptions, we carried out an ecologicalphytocenotical classification of communities of the Tamariceta laxae formation, widespread in the Republic of Dagestan, which includes 2 groups of associations and 3 associations.

Group of associations Tamariсeta laxae
Communities group of associations Tamariseta laxae are found on the Terek-Sulak lowland to the lower mountain belt, on sands and salt marshes.
The projective cover of the shrub layer is 35%, of the grass layer 25%. In the group of associations Tamariсeta laxae, the background species of the shrub layer is Nitraria schoberi, Tamarix laxa, Salsola glauka. Artemisia taurica, Leymus racemosus, Medicago caerulea, Frankenia hirsuta, Phleum phleoides take on the role of dominants of communities of this class of associations in the herbaceous layer.

Group of associations Medicageta minimae
The group of associations Medicageta minimae is found on the salt marshes of the Terek-Sulak lowland to the lower mountain belt.
The projective cover of the shrub layer ranges from 10 to 20%, and of the herbaceous layer from 50 to 55%. In the communities of this group of associations, the background species of the shrub layer are Nitraria schoberi and Tamarix

Discussion
According to the conducted studies using the ecological-phytocenotical method of communities with the participation of Nitraria schoberi 5 formations, 12 groups of associations and 25 associations were identified in Dagestan.
No one has studied the communities with the participation of Nitraria schoberi on the territory of Dagestan. Work was carried out to study a similar flora using the ecologicalphytocenotical method on the territory of Kalmykia [4,23]. Studies have also been carried out from the standpoint of the ecological-floristic approach to study the communities of steppe vegetation where Nitraria schoberi directly grows [24][25][26]. Based on the results of both their own studies and the results of other authors, it is necessary to carry out a comparative assessment of the species richness of communities with the participation of Nitraria schoberi.

Conclusion
There are many species in need of protection in the populations of Nitraria schoberi, which have a high phytosociological value, as they are represented by rare and endemic vegetation types of Dagestan.
For the first time, an ecological-phytocenotic classification of communities with the participation of Nitraria schoberi widespread in the Republic of Dagestan has been developed. The current state of these communities with the participation of the Dagestan Red Data Book species Nitraria schoberi at the present time remains unsatisfactory. On the basis of the classification, more valuable and rare communities will be recommended, the study and monitoring of which will allow preserving and predicting the further development of areas that are on the verge of extinction and are subject to constant anthropogenic pressure.