The study of the floristic and coenotic diversity of Daghestan forests was being conducted for about a century. It was started by N. A. Bush (1905) and N. I. Kuznetsov (1911). Later A. A. Grossheim (1925) gave a brief description of birch, pine and mixed forests in the limestone region of internal mountain Daghestan. A significant contribution to the study of these forests was done by I. I. Tumadzhanov (1938), M. M. Magomedmirzayev (1965) and P. L. Lvov (1964). However, despite of the large number of papers on the forest vegetation of Daghestan, the Koch pine (Pinus kochiana Klotzsch. ex C. Koch) forests, which occupy about 75 000 hectares (17 % of the forest area of the Daghestan), were studied poorly.
The present study is based on the data of field study by the authors in several districts of foothill Daghestan, internal mountain Daghestan and high mountain Daghestan in 2012–2016 within key-areas. The releves were carried out using the standard methods (Methods…, 2002) on 99 sample plots of 20×20 m. In addition, relevйs collected by Tumadzhanov (1938) and Magomedmirzayev (1965) were used for the syntaxa characteristic. Totally 140 relevйs were included into analysis. The classification of Pinus kochiana communities was made using the dominant-determinant approach of Russian geobotanical school founded by V. N. Sukachev. Syntaxa names are given according to the «Draft Code of Phytocoenological Nomenclature» (Neshataev, 2001).
The Prodromus and the diagnostic features of the syntaxa are presented. The entire set of 140 releves was referred to the formation Pineta kochianae differing fr om Pineta sylvestris, not only by dominant species, but also by species composition and community structure. The most constant species occuring in the majority of associations are Juniperus oblonga in the shrub layer; Calamagrostis arundinacea, Fragaria vesca, Galium valantioides, Thalictrum foetidum in the herb and dwarf-shrub layer; Rhytidiadelphus triquetrus in the moss one. Six groups of associations and 28 associations were distinguished. The main diagnostic features of association groups (Table 1), phytocoenotic and synoptic tables for associations (tables 2–13) are presented.
The density of tree layer in Pinus kochiana stands varied from 0.3 to 0.9. The pine trees at the age of 100 years have a height from 5 to 25 m (usually 10–15). The Pinus kochiana stand yield class (bonitet) varies from Va to III class; stands of IV class predominate. In the tree layer the following species occur in different associations: Acer platanoides, A. trautvetteri, Armeniaca vulgaris, Betula litwinowii, B. pendula, B. raddeana, Carpinus caucasica, Fagus orientalis, Fraxinus excelsior, Juniperus oblonga, Malus orientalis, Populus tremula, Pyrus caucasica, Quercus macranthera, Q. petraea, Q. pubescens, Q. robur, Salix caprea, Sorbus aucuparia, Taxus baccata, Tilia begoniifolia, T. cordata. In the understory the young growth of Betula litwinowii, B. pendula, B. raddeana, Juniperus oblonga, Sorbus aucuparia, Taxus baccata, Ulmus glabra occur. The shrub layer is usually well developed; its density is up to 60 %. The most constant species of the shrub layer in different associations are Berberis vulgaris, Cotinus coggygria, Cotoneaster integerrimus, Daphne glomerata, D. mezereum, Juniperus oblonga, Lonicera xylosteum, Rhododendron caucasicum, R. luteum, Rosa oxyodon, R. pimpinellifolia. On the upper border of forest belt wild raspberry (Rubus idaeus) and dwarf-shrubs (Empetrum caucasicum, Vaccinium myrtillus, V. vitis-idaea) often occur.
Altogether 487 species of herbaceous plants were found in studied communities. Perennial forbs and grasses predominate. Ecological-cenotic groups of species (mesophytes, xerophytes and mesoxerophytes) are represented equally. 107 species of Bryopsida and 3 of Marchantiophyta are found, the moss cover varies from single individuals to 90 %. Only few species of epiphytic lichens and single lichens on wind fallen trunks are met.
Koch pine forests which are widely spread on the northern slopes at the altitude more than 1200 m above the sea level, occur mainly on rocky slopes, formed by sandstones, limestones or clay slates in regions with different climatic conditions — from the dry climate of the foothills to the humid and cold climate of the high mountain Daghestan. Their species composition, set of dominants and community structure depend on the soil type, altitudinal position and the type of underlying rock. Three ecological groups are distinguished: 1) mesophytic pine forests, including moss-rich, rhododendron-rich and mesophytic-grass-herb-rich, 2) xeromesophytic ones with Carex humilis and Brachypodium pinnatum and 3) mezoxerophytic with Quercus pubescens, Cotinus coggygria, Poa bulbosa, etc. (Abdurakhmanova et al., 2015).
Within the area of shale part of high mountain Daghestan most common are moss-rich and herb-rich pine forests with boreal, nemoral and Caucasian mesophilic species dominance, which occur at the upper forest lim it. The petrophyte group of associations on rocky sites was first revealed. The Salvia-Onobrychis-rich Koch pine forests (with Salvia canscens and Onobrychis cornuta) are similar to the phryganoid communities on limestone rocks influenced by overgrazing and selective cutting. Koch pine forests of Southern and Foothill Daghestan are characterized by the absence of boreal species common for the forests of high mountain Daghestan.
The replacement of pine by other tree species mostly depends on soil conditions and altitudinal position. In the broad-leave forest belt pine is replaced by deciduous tree species better on deep fertile soils than on the shallow soils with low humus content. In contrast to the Western Caucasus, the replacement of pine by spruce (Picea orientalis) and fir (Abies nordmanniana) is never observed in Daghestan due to the absence of these species in it flora.
Currently, the climate conditions of Daghestan are quite favorable for the distribution of pine forests. In comparison with other tree species the expansion of Pinus kochiana, supported by a decrease in livestock grazing and decrease in agricultural use, has increased.
Comparative analysis of Scots pine homogeneous stands bioenergetic productivity in European North
