Forest ecosystems in the upper reaches of the Malka River (Central Caucasus): typology, floristic composition, current state

According to the results of the study, it found that in the upper reaches of the Malka River, the most common is the group of birch forests with tallgrass vegetation cover, including Betuletum calamagrostioso-herbosum. Smaller areas occupied by group of complex herbaceous birch forests, represented by Pineto-betuletum calamagrostioso-herbosum and a group of pine forests with herbrich vegetation cover, including Pinetum calamagrostioso-herbosum. Forest stands are mainly singlestorey, medium and low-density, bonitet classes II-IV. The floristic composition of the Malka River basin forests includes 101 species from 68 genera and 38 families. Forest ecosystems of the study area are home to four species of vascular plants included in the list of protected taxa of the KabardinoBalkarian Republic: Betula raddeana Trautv, Vaccinium myrtillus L., V. vitis-idaea L., Allium victorialis L. Among protected lichen species, we found – Leptogium burnetiae C. W. Dodge, Letharia vulpina (L.) Hue, Lobaria pulmonaria (L.) Hoffm.), Lobarina scrobiculata (Scop.) Nyl.), Sticta sylvatica (Huds.) Ach. and Usnea florida (L.) Weber ex F. H. Wigg. The article analyzes the geographic spectrum of the forest flora of vascular plants and lichens, including 12 geographic elements, with the boreal geoelement predominating. The lichen flora dominated by boreal geoelements.


Introduction
The Malka River originates on the northern slopes of Mount Elbrus from the confluence of the Kyzylsu and Karakayasu Rivers, taking tributaries of mountain streams, rivulets. The basin of the river in its upper course covers the northern part of the National Park " Prielbrusie" and adjoining territories -the reserve "Malkinskiy", vicinities of the village Khabaz. Relatively steep nearvalley slopes are covered with forest vegetation. In contrast to the forests of the southern Prielbrusie (valley of the Baksan River), the northern forests are rather wellpreserved, which is due to an insignificant anthropogenic load in the absence, until recently, of federal road communications. Only in 2010, a road was built that goes to the upper river to the mineral springs, which increased the recreational impact on the surrounding ecosystems. During the season, more than a thousand unorganized tourists camp at the springs of Dzhily-Su.
Subalpine forests in the upper reaches of the Malka River, which are of great ecological importance, represented by both pure and mixed birch and pine forest stands. On the one hand, they fulfil an anti-erosion and environmental protection role and, on the other hand, they provide habitat for a number of mammal and bird species, in particular, those listed in the Red Books of Russia [1] and the Kabardino-Balkarian Republic [2]. The forests of the northern Prielbrusie are considered unstudied. We could not find any publication devoted to their study.
Complex orographic conditions of the area contribute to a great diversity of plant, including forest, communities. In this regard, the establishment of the typological structure of forests in the upper reaches of the Malka River, assessment of their species diversity and current state are relevant.
In connection with the above, the purpose of this work is to assess the typological structure, floristic composition, and current state of birch and mixed forests in the basin of Malka River.

Study area
Were the studies carried out in 2016-2019 by a detailed route method in the basin Malka River within the altitudes of 1100-2000 m above sea level (figure). Landscapes are relatively steep near-valley slopes of ridges, under pine and birch forests on mountain-meadow and mountainbrown forest soils. The total forested area of the upper Malka River is 311 km 2 .
We conducted studies the studies in the Central Caucasus (between 42°54'-44°01' N and 43°52'-43°03' E) within the elbrusskiy variant of vertical zonation of the northern macroslope in the Central Caucasus in 2016-2019. The lack of broad-leaved forest belt and pronounced xerophytization of landscapes determine the peculiarities of the elbrusskiy variant of vertical zonation [7]. Its belt spectrum consists of meadow steppes (foreststeppes), steppe meadows, subalpine, alpine, subnival and nival belts.
The mountainous relief, altitude above sea level, and the arrival of western air masses from the Atlantic form a relatively cold and humid continental climate of the study area in mountain regions. The climate of the lowland regions is continental, relatively hot and dry.

Data collection and measurements
To study the composition and structure of the forests of the study area, we carried out geobotanical descriptions on sample plots of 30×30 m in size using standard methods accepted in geobotany and forest inventory [8][9][10][11]. We established 31 model plots. Based on the tier structure of vegetation, a complete floristic list compiled, and forest taxation characteristics were determined. The stand structure, stand shape, crown density, average height, average diameter, number of trunks, and fullness were evaluated. The species affiliation of vascular plants was determined according to A.I. Galushko [12].
In addition to species composition and projective cover, the average height and the number of specimens of each species on the site recorded for the undergrowth. The total projective cover, species composition, and projective cover of individual species were determined in the study of the dwarf shrub-herb layer.
The dominant approach used to classify forest vegetation, and forest type considered as a type of forest biogeocenosis. Groups of forest types distinguished by the species composition of the stand, as well as by the groups of dominant species in the herb-bush and moss tiers. One forest type included phytocenosis that were similar in the species composition of the stand tiers [10,11]. Latin names of vascular plants and mosses given according to PlantList [13].
The lichen flora of the sample areas derived from woody and soil substrates. The collected material cameralized using comparative-morphological and comparative-anatomical methods using light microscopy. The lichens nomenclature of taxa generally follows recently published checklists for Scandinavia and North America [14,15].
For the phytogeographic analysis of the flora of vascular plants, the geographic element spectrum in the work based on the scheme compiled by N.N. Portenier for the Northern Caucasus [16]. The geographic elements of the lichen flora distinguished based on the zonal principle developed by Oxner [17,18] and developed in the works of several authors [19,20].
The study of understory regeneration of forestforming species on the territory of the northern section of the National Park "Prielbrusie" conducted by laying test plots of 3×3 m, laid one by one along the diagonal of the test area, for 40-45 per one ha. The number, height, diameter, and age of shoots and undergrowth were recorded [21]. When undergrowth and shoots were recorded, they were distributed by height into four groups: I -0-0.50 m; II -0.51-1.00 m; III -1.01-1.50 m; IVmore than 1.50. We visually evaluated its distribution in the sample area, as well as its qualitative condition. To assess natural regeneration, we used the scale proposed by S.M. Bebia [22].

Floristic composition and ecosystem diversity of forests in the Malka River basin
The studied forest biogeocenoses, located in the conditions of a specially protected natural area, did not experience logging, but asubjected to recreational pressure. According to the results of the studies, it found that in the upper reaches of the Malka River; most of the area is birch forests, represented by a group of high-grass birch forests. Forest massive areas are located on slopes of western, northern and north-western exposures. We found 3 species of birch trees: Betula litvinowii Doluch., B. pendula L., B. raddeana Trautv. The accompanying species is Pinus sylvestris L. Undergrowth is almost absent, with isolated sightings of Salix caprea L., Sorbus aucuparia L., Rubus idaeus L., Lonicera steveniana Fisch. ex Pojark. The ground cover is rich in species, multilayer.
In the group of birch forests with tallgrass vegetation cover, according to the results of the research, one type of forest described: Betuletum calamagrostioso-herbosum.
A group of complex herbaceous birch forests, including Pineto-betuletum calamagrostioso-herbosum, occupies small areas in the study area. Forest areas of complex birch forests are located on slopes of western, northern and northwestern exposures, with a steepness of 20°-30°. The stands of complex composition, in addition to Betula raddeana, B. litwinowii, B. pendula in its formation involves Pinus sylvestris. Plantations of different age, two-tiered, III-IV bonitet classes, crown closeness -0.5. Undergrowth is rare (projective coverage -10%), formed by Salix caprea, Lonicera steveniana.
The background vegetation in the Malka River gorge also created by small area pine forests, the main massifs are represented by a group of pine forests with herb-rich vegetation cover, including Pinetum calamagrostiosoherbosum.
Forest stands are clean, single-tiered, formed by Pinus sylvestris, single B. pendula noted. Forest areas are located on slopes of northern and north-eastern exposures, with a steepness of 20°-40°. Closure of crowns -0.6.
The undergrowth layer is not expressed, projective cover is less than 10%, includes Juniperus communis L., Rhododendron luteum Sweet. Forest regeneration is very weak; the undergrowth is reliable, represented by Pinus sylvestris.
Below are the taxation characteristics of the sample areas of the selected forest types (Table 1). A comparison of the identified forest types in terms of floristic similarity shows that the closest forest types are Betuletum calamagrostioso-herbosum and Pineto-betuletum calamagrostioso-herbosum, which explained by similar growing conditions. Pinetum calamagrostioso-herbosum, occupying the slopes of the northern exposition, differ in their floristic composition, and the similarity coefficient between this type of forest and Betuletum calamagrostiosoherbosum and Pineto-betuletum calamagrostioso-herbosum is rather low (Table 2).
In the flora of birch and pine forests of the Malka River basin, according to the results of our studies, 101 species of vascular plants from 68 genera and 38 families identified.  (1) The lichen flora of the Malka River headwaters forests represented by 37 species (Table 3). Most of them are epiphytes -78% of the total number, followed by epigeous and epilithic species -15 and 7%, respectively. The following protected species found:
4. Circumboreal element. One of the smallest by number of species element of forest flora, Malka river basin, presented by one species (0.99%) -Linnaea borealis.
5. Panboreal element. One species -Gymnocarpium dryopteris found in the forest flora of the studied area.
6. Euro-Siberian element. In the forest flora of the studied area, we noted 25 such species ( 9. Euxine element. We recorded one species (0.99%) -Carum meifolium in the forests of the upper Malka River.
12. Caucasian-Armeno-Iranian element. One such species, Juniperus communis var. saxatilis Pall., recorded in the forest flora of the Malka River basin.
The core of the studied lichen flora is the boreal element -18 species (Figure 2). Among boreal lichens, the Holarctic distribution group is represented by nine species, eight of which are distributed circumboreally: Evernia divaricata, Imshaugia aleurites, Melanelia olivacea, Vulpicida pinastri, Usnea cavernosa, U. dasopoga, U. hirta, U. florida. Hypogymnia tubulosa is a species with considerable disjuncture of areal in Holarctic, its range covers Europe, Asia, North America, in its distribution gravitates to oceanic areas.
Boreal species of multiregional distribution are bipolar. Species of this group are widely distributed in green-moss forest type, where they play an important phytocenotic role, being subdominants in epiphytic, epixilic and epigeic communities. Such species as Bryoria fuscescens, Hypogymnia physodes, Platismatia glauca form trunk sinusia. Cetraria islandica, Cladonia rangiferina, Peltigera malacea, Stereocaulon paschale dominate in the ground cover. On decaying wood the above mentioned H. physodes, and also Leptogium saturninum occur. Pseudevernia furfuracea selects habitats with favorable temperature conditions.

Undergrowth accounting in forest areas of the Malka River basin
It is known that the number of undergrowth depends on many factors [23,24], including the type of forest and crown cover [25], in this regard, the intensity of reforestation was evaluated in the most common types of forests in the study area. When studying regeneration, we evaluated the quantitative and qualitative condition of the undergrowth on the sample plots, its age structure, and the nature of distribution on the sample area. According to the results of the studies, it was found that forest regeneration in forest areas of Malka river basin is very weak ( Table  4). The ability of forest forming species to natural regeneration, along with climatic parameters of environment and soil conditions, is influenced by relationships between species of forest biocenosis tiers. In our opinion, the very weak forest regeneration on the sample plots of the study area is due primarily to the fact that the well-developed multilayer ground cover (total projective cover -up to 80%), prevents the emergence of seedlings or inhibits their growth.Low density of the stand on these plots contributes to the good development of the grass layer.
The quality of undergrowth subdivided into reliable, doubtful, and shrunken. For the majority of sample plots, we noted the growth of reliable undergrowth. Undergrowth distribution on forest plots predominantly clustered, confined to natural "windows" of the stand, to forest edges.

Conclusions
The main diversity of forests in the upper reaches of the Malka River represented by three forest types, which are included in three groups. The types of birch and pine forests differ in the species composition and dominants of the lower tiers of stands, which reflects the peculiarities of habitats. The most widespread in the territory of the Malkinskiy Zakaznik is a group of birch forests with tallgrass vegetation cover, formed by Betula raddeana, a species included in the Red Book of the Russian Federation, the Red Book of the KBR, status -rare species. The ground cover in this group is formed representatives of forest tall grasses -Calamagrostis arundinacea, Aconitum nasutum, Geranium sylvaticum and others. S.Kh. Shkhagapsoev and L.B. Kurasheva [6] also distinguish birch forests with rhododendron undergrowth and subalpine bilberry forests for the territory of Kabardino-Balkaria, which not found in the upper reaches of the Malka River.
The lichen flora is dominated by the boreal geoelement (48.65%), indicating that, despite the relatively southern location of the mountainous part of Kabardino-Balkaria, a pronounced connection with the lichen flora of more northern regions is typical.
The obtained data characterize the current state and typological diversity of forests in the upper reaches of the Malk River and can subsequently serve as a basis for the assessment of successional changes in the forest cover and the dynamics of vegetation diversity.
Flora of birch and pine forests of the Malka River basin includes relicts, endemics, protected species of plants and animals; therefore, their preservation is the most important nature protection task. Large mammals such as bears, wild boars, roe deer, and a considerable number of bird species (snake eagle, peregrine falcon, golden eagle, black vulture, and Caucasian grouse) found in birch forests bordering the belt of broad-leaved forests. A number of bird species nesting, others are migratory. Suitable habitats are preserved here for such rare mammal species as the Caucasian otter and the European mink, as well as, numerous in the past, the red deer, the Caucasian tour.
The studies were carried out as part of state assignment no. 075-00347-19-00 on the topic "Patterns of the Spatiotemporal Dynamics of Meadow and Forest Ecosystems in Mountainous Areas (Russian Western and Central Caucasus)."