REGIONAL fEATURES Of THE ALTITUDINAL GRADIENTS IN NORTHERN TRANSBAIKALIA VEGETATION COVER

According to the the biome concept, the idea of the orobiome and its significance in the evaluation of the biodiversity for mountain territories are disclosed. Altitudinal gradients of vegetation with certain altitudinal limits of development are the basis for analysing the floristic and coenotic diversity of the orobiome and the ecological and geographical patterns of its spatial organization at the regional level. Based on the example from Kodar-Kalar orobiome, an altitudinal composition of the vegetation of the Northern Transbaikalia has been identified using thematic maps. The statistical evaluation of the altitudinal distribution of 4 vegetation belts (the upper tundra belt, the tundra belt, the sub-tundra belt and the mountain taiga belt) has been made. The regional features of the altitude position of the basic vegetation types forming the belts have been determined for the orobiome. They are reflected in three geographical variants. Orographic conditions and the history of the territory development have been discussed in the analysis of regional features of altitudinal spectra difference. KEY wORDS: orobiome, altitudinal structure of vegetation cover, vegetation belts, the


INTRODUCTION
According to the altitudinal gradient of bioclimatic conditions in the mountains, an altitudinal structure of vegetation cover forms.It is associated with regular changes in species richness (Sang 2009;Wiesmair et al. 2017), coenotic diversity (Hemp 2006;Molozhnikov 1986) and spatial structure (Nakashizuka et al. 2016).These particularities have regional features that determine the separation of the altitudinal spectra of vegetation, which is reflected in the typology of altitudinal zonation, with the identification of its groups and classes (Ogureeva 1991).The geography of the botanical diversity of mountains is revealed on the basis of the biome concept (Walter and Breckle 1999).The idea of biomes is based on the concept of geographic dimensions of geosystems at the global, regional, and local levels.The biome is considered to be a combination of ecosystems of different levels, including the biota that most effectively uses the abiotic components of the environment as a result of a specific, historically conditioned adaptation to them.
The biome concept was used as a strong basis for creating the map «The Biomes of Russia» (2018).The map legend was based on the classification of terrestrial ecosystems-biomes, which includes three major categories, namely the zonobiome, the orobiome (altitudinal vegetation belts spectra in the mountains) and the pedobiome, where there are large edaphic variants in the zonal types of ecosystems.For each orobiome, the regional specificity of mountain biota was shown.Its role in the belt structure of the vegetation cover as the basic component of structure and diversity in mountain ecosystems was determined (Ogureeva and Bocharnikov 2017).
The botanical diversity of orobiomes is revealed through the altitudinal structure of the vegetation cover and includes floristic and coenotic components.Taxonomic and coenotic diversity is considered by taking into account the basic vegetation formations that have certain altitudinal limits.
So, in the regional evaluation of the botanical diversity of orobiomes, one of the key problems is the identification of the altitudinal spectra of vegetation and the altitudinal limits of the distribution of their divisions.This allows for a comparative geographic evaluation of diversity and the identification of key factors that determine the differentiation of biota at the regional level.This analysis becomes especially valuable for infrequently studied mountain areas, one of which is the Northern Transbaikalia.
The main objective of this investigation was the identification of the belts structure and biodiversity of the Kodar-Kalar orobiome and its geographic variants, developing in the conditions of the mountain systems of the Northern Transbaikalia.The characterization of the typological diversity in the structure of altitudinal zonation vegetation at high hierarchical levels, the statistical evaluation of the altitudinal limits of vegetation belts and an analysis of altitudinal zonation within the different geographic variants of the Kodar-Kalar orobiome were the main tasks of this work.The Kodar-Kalar orobiome and its three geographic variants (the North Baikal, the Patom and the Kodar-Kalar) developed in the vast mountainous territory of the Northern Transbaikalia within the North Baikal, Stanovoy and Patom highlands (Fig. 1).The largest ridges are 2500-3000 m above sea level and have a sub-latitudinal strike (Upper Angarsk, North and South Muisky, Kodar).The vast surfaces of the intermountain depressions (Upper Angara, Muya-Kuanda, Chara) are confined to the Baikal rift zone (Fig. 2).

MATERIALS AND METHODS
The Kodar-Kalar orobiome refers to the Transbaikalian group of orobiomes.It is characterized by the meanings of the bioclimatic characteristics (average annual air temperature, sum of active temperatures and the average annual rainfall), number of species of the main groups of terrestrial organisms (vascular plants, bryophytes and lichens; mammals, birds, reptiles and amphibians).The floristic diversity of the Kodar-Kalar orobiome is represented by more than 800 species of vascular plants and more than 300 species of bryophytes in each geographic variant (map «The Biomes of Russia» 2018).With a similar character of the altitudinal zonality of vegetation, their differences should be sought in the altitudinal limits of the belts and their biodiversity.
Investigations of the spatial structure and biodiversity of mountain vegetation were carried out on the basis of concepts of the types of altitudinal zonation and their classification (Ogureeva 1991) and the biome ecosystem concept (Olson et al. 2001;Walter and Breckle 1991).The vegetation cover of orobiomes was considered through the ecologicaldynamic connections of plant communities within each belt and on the whole for the entire altitudinal spectrum.The regional analysis of the botanical diversity of orobiomes allowed us to understand the uniqueness of orobiomes and the features of their geographical variants.
The investigation was based on the analysis of cartographic works and remote sensing data which can be used to determine the vegetation structure (Litinsky 2017).As the initial map data, at the first stage a digital map of Russia's vegetation cover, based on the processing of MODIS images with a spatial resolution of 230 m (Bartalev et al. 2011) was used.At the second stage a smallscale map of vegetation in the south of Eastern Siberia (scale 1: 1 500 000), executed at the Institute of Geography of the SB RAS (Belov 1973), was used.The legend of this map was based on a geographic-genetic basis, taking into account the dynamic trends in the vegetation cover (for a number of root types of communities, their derivative variants are given).This map was digitized and used as a shp-file.
A statistical analysis of the connection between the basic subdivisions of the vegetation cover and the absolute height of the terrain was carried out.Basic plant communities in the mountains are determined by the position on the indigenous slopes in different exposition and steepness.They have a phytocoenotic optimum at a certain altitudinal levels on which the construction of the altitude spectrum is based (Ogureeva 1991).
The absolute altitude values were derived from the digital elevation model used to create the WorldClim bioclimatic layers (Hijmans et al. 2005).It was represented by a raster surface with a spatial resolution of 0.0087°.This resolution was used as the basis for assessing the connection of vegetation cover with altitude (meters above sea level), which is optimal for a small-scale survey.
For the statistical analysis, the raster layer of absolute heights was trimmed by the mask of the surface layer of the Kodar-Kalar orobiome (Spatial Analyst module, Extract by Mask tool).Geographical reference of the vegetation map of the southern part of Eastern Siberia was carried out on the basis of reference points using a 6th degree polynomial model (WGS-84 coordinate system).
The statistical estimation of the altitudinal distribution of vegetation was carried out by means of the conjugate analysis of vector layers of vegetation units using a raster model of the relief on the basis of its spatial resolution.The main statistical indicators of absolute heights were used: mean, median, standard deviation, maximum and minimum values, and coefficient of variation (Zonal Statistics tool).Along with the descriptive statistics, regression analysis techniques were used to estimate the change in the frequency of occurrence of vegetation units throughout the entire range of absolute heights.The changes were determined by the trend line constructed by the linear filtration method with a smoothing of 50 points.The mean and standard deviation of the basic vegetation for the belts served as the basis for the identification of optimal conditions for the development of vegetation units for each belt.The boundaries between belts and sub-belts were determined on the basis of the weighted average of absolute altitudes, within which basic plant communities are common for vegetation belts.The significance of the absolute heights for vegetation belts was determined by Student's t-test.
All operations with cartographic materials were conducted in the ArcGis 10.0 program.The statistical analysis was performed using the thematic tools of ArcCatalog, as well as SPSS 11.5.

RESULTS AND DISCUSSION
The botanical diversity of the Kodar-Kalar orobiome is formed under conditions of pronounced altitudinal-belt differentiation by a significant gradient of absolute heights (from 200 to 3000 m).(Florensov 1968).The continental cold climate with pronounced altitudinal differentiation of the heat and moisture content parameters determines the key bioclimatic conditions for the formation of the altitudinal vegetation spectrum.
Three geographical variants reflect the differences in the structure of the altitudinal zonation of vegetation in the orobiome.They are associated with the regional morphostructural features of the territory, which are reflected in the vegetation cover.
The relief of the Stanovoy highland, which is associated with the development of the North Baikal and the Kodar-Kalar variants, is determined by the conditions of the Pliocene-Holocene orogenesis (Florensov and Olyunin 1965).The modern relief was influenced by the ancient glaciation, which is associated with the alpine type of relief of the highlands.In the conditions of the continental climate (Kodar, Udokan, South Muya ridges), the high-mountain (tundra) type of highland, dominated by the continental regions of the boreal zone with development of cryogenic processes, is formed (Korner 2013;Tolmachev 1948).The intermountain depressions are confined to the rift zone.The vast surfaces of depressions are composed of thick layers of loose lake and alluvial sand deposits (Zorin 1971).The Patom highland, developed on a folded base with well-defined areas of ancient equalization surfaces, has a prevailing height of 1200-1300 m (up to 1771 m).The Patom highland is rather poorly transformed by the latest tectonic movements.The erosiondenudation middle-mountain relief with narrow, deeply incised valleys predominates.
The Kodar-Kalar orobiome belongs to the group of Transbaikalian boreal (taiga) orobiomes (map «The Biomes of Russia» 2018).It is characterized by a generality in the structure of the biota and vegetation cover.
The vegetation cover of the highlands refers to the tundra type.It is represented by complex combinations of communities of larch, spruce (Picea obovata Ledeb.) and birch (Betula lanata (Regel) V.N.Vassil.)sparse forests, Pinus pumila (Pall.)Regel communities and high-mountain tundra.
Analysis of the vegetation map of Russia (Bartalev et al. 2011) At the first stage of revealing the Kodar-Kalar orobiome vegetation structure, an analysis of the digital map «Vegetation cover of Russia» (Bartalev et al. 2011) was carried out.The legend of the map includes 20 typological units within the Kodar-Kalar orobiome.Seven units are interpreted as basic in the composition of the vegetation belts.Using the frequency of occurrence, an altitudinal evaluation of the units was determined (Table 1).Pine and larch forests, cedar pine and shrub tundra are characterized by the unimodal normal distributions of their occurrence in absolute heights (based on the spatial resolution of the digital elevation model) (Fig. 3).These typological units are quite strictly gravitating to a specific altitude level within the orobiome, forming belts of vegetation with a predominance of mountain taiga, Pinus pumila communities, and mountain tundra communities.The values of the standard deviations characterize the area of their optimum distribution.The larch forests (Larix gmelinii) are confined to heights of 550-1100 m.In general, this is in agreement with the data on the altitudinal distribution of larch forests, which form the mountain taiga belt in the structure of the altitudinal zonation of the Stanovoy highland (Peshkova 1985).Pine (Pinus sylvestris L.) forests, confined to the lower part of the mountain taiga belt (500-600 m), have small deviations from the normal distribution at several altitude levels (Fig. 3).This is due to their distribution in the intermountain depressions.In the bottoms of these depressions at altitudes of 600-700 m, they widely predominate on sand deposits.
Table 1.The statistical values of the altitudinal distribution of the typological vegetation units for the Kodar-Kalar orobiome and its geographic variants (according to the vegetation map of Russia).The identification of the generalized spectrum of altitudinal zonation of vegetation and the specification of the altitude limits of the distribution of plant communities within the Kodar-Kalar orobiome and its geographical variants were carried out on the basis of the conjugate analysis of the vegetation map of the south of Eastern Siberia (Belov 1973) using a digital elevation model.The coenotic diversity of the orobiome was determined at the level of 30 typological units, allocated on the basis of a geographicgenetic classification taking into account the dynamic state of vegetation.According to their typological composition, they are classified into 4 belts, including 6 subbelts (Table 2).In connection with the absolute height, they are characterized by significant differences in the values of the basic descriptive statistics.Significant intersections of vegetation formations that form different belts on an altitudinal gradient are revealed in the analysis of standard deviations from occupied average heights, which is expressed in the active interpenetration of communities of different belts along the altitudinal gradient.

I -the
The typological units of vegetation cover, ranked at medium height, are characterized by a distribution that is best explained by exponential dependence, with the index R² = 0.97, because the Kodar-Kalar geographical variant has the highest value on a linear trend (R² = 0.98) (Fig. 5).This type of distribution of vegetation along the altitudinal gradient is associated with a decrease in the coenotic diversity in the mountain taiga belt.There are coenotic poorly herbaceous and shrubby-lichen pine forests developed in the lower part of the mountain taiga belt.They are developed in the Chara intermountain depression and grow here in combination with birches, meadows and grassy marshes (Garashchenko 1993).The altitudinal limits of the belt were determined from the weighted average heights, on which the basic vegetation communities of each belt find optimal development (Table 3).The use of mean values on the interval between the weighted average values of neighbouring belts made it possible to determine the altitude amplitudes of their development, as well as the boundaries between the belts (Table 4).The regional specifics of the spectra within the Kodar-Kalar orobiome were reflected in the altitudinal spectra -generalized models of the altitudinal vegetation organization, showing the general features of its structure (Fig. 6).
The dominant larch mountain-taiga belt, the fragmented development of dark coniferous-taiga forests, the formation of the high-mountain vegetation system with the participation of the Siberian dwarf pine communities, mountain tundra and the extremely limited participation of alpine vegetation are the system-forming characteristics of the revealed altitudinal belt structure.
Table 3.The weighted average of absolute altitudes and their standard errors for altitudinal belts and sub-belts of vegetation for the Kodar-Kalar orobiome and its geographic variants (by basic vegetation communities in altitudinal subdivisions) (geographic variants names -see Table 1) Table 4.The structure of altitudinal spectra of vegetation of geographical variants of the orobiome is associated with the orographic structure of the territory.With an increase in the average altitudes of the ranges, the proportion of the sub-tundra and tundra belts in the vegetation cover increases (the Kodar-Kalar geographic variant).The expansion of the mountain taiga belt and the increase in its coenotic diversity occur in conditions of predominance of middle relief (the Patom geographical variant).The increase in the area of belt development does not always entail an increase in the diversity of communities.
In a generalized form, the structure of the vegetation cover of the Kodar-Kalar orobiome is represented by 4 altitudinal belts and 6 sub-belts of vegetation, which have certain characteristics of distribution and diversity.
I. The upper tundra belt (1900-3000 m).This belt has fragmentary development on the highest ridges with a large altitude amplitude.Fragments of moss-lichen tundra and, in some places, alpine meadows prevail in the rare vegetation cover.II.The tundra belt (1330-1900 m).This belt is confined to the upper parts of ridge ranges.It can get down to the upper limit of the mountain taiga belt along rocky slopes.In the altitudinal spectrum of the vegetation of the Patom geographical variant, the firpine-spruce (Picea obovata, Pinus sibirica, Abies sibirica) forests sub-belt in the lower part of the mountain taiga zone is well developed.The greatest diversity is in the northern and north-western parts of the territory of the orobiome in contact with the taiga of the Central Siberian Plateau.In the altitudinal spectrum, the mountain taiga belt is developed up to an altitude of 800-900 m.The specificity of the variant is related to inversion within the sub-tundra belt.
The Siberian dwarf pine sub-belt is located bellow the sparse forests sub-belt.This is due to active contact below the tundra and mountain taiga vegetation along the slopes of ridges in the Patom highland.
The Kodar-Kalar geographic variant is characterized by the highest altitude amplitude of the high mountain vegetation due to ridges at great altitudes (BAM peak -3073 m), active modern glacial activity and the complex orographic structure.The variant has low typological diversity in the larch-pine and fir-pine-spruce forests sub-belts, which are formed in the Chara depression.It is characterized by a complex structure with small fragments of pine with Rhododendron dauricum forests, sedges (Carex lasiocarpa Ehrh., C. vesicata Meinsh., C. rostrata Stokes), and grass (Poa palustris L., Calamagrostis neglecta (Ehrh.)Gaertn., B. Mey. and Schreb.)meadows with fragments of mires (Garashchenko 1993).The upper boundary of the forest is located at altitudes of 1100-1200 m, and the tundra belt begins from an altitude of 1400 m.The specificity of the Kodar-Kalar variant is associated with the distance from the South Siberian and Baikal regions of the formation of floristic and coenotic diversity.

CONCLUSION
The revealed altitudinal structure of the vegetation cover of the Kodar-Kalar orobiome is the basis for the biodiversity evaluation.
The patterns of spatial differentiation of biodiversity within the orobiome are associated with the integrated effect of altitudinal zonality.This is reflected in the formation of the 4 belts of vegetation: the upper tundra belt, the tundra belt, the subtundra belt (the Siberian dwarf pine sub-belt, the sparse forests sub-belt) and the mountain taiga belt (the larch forests sub-belt, the larch-pine sub-belt and fir-pine-spruce forests sub-belt).The spatial organization of the vegetation of the Kodar-Kalar orobiome is determined by the regularities at the altitudinal belt level and in connection with regional features that are determined by orographic conditions (the size and orientation of the ridges, the presence of intermountain depressions) and the history of the territory development.Among the key features of the botanical diversity of the orobiome and its spatial structure at the regional level, the following should be noted.
Vegetation communities associated with the Baikal-Dzhugdzhur natural area are more important communities in the vegetation cover of the Kodar-Kalar orobiome.They participate in the formation of the mountain taiga belt (larch forests of the Angara (Eastern Siberian) geographic and genetic complex), the sub-tundra belt (the Siberian dwarf pine communities of the Beringian complex) and the mountain tundra belt.Dark coniferous forests have fragmentary development in river valleys, steppes are locally developed on the southern slopes of ridges.
The dominance of larch forests, the low position of the upper boundary of the forests, and the wide altitude amplitude of the tundra belt determine the key features of the altitudinal zonality of the vegetation cover in the orobiome and its regional specificity.
The most important altitudinal features in the vegetation cover fall to 1000 m, at which the sub-tundra belt is changing to the mountain taiga belt, and to 1300 m -the lower boundary of the upper tundra belt.
Geographical variants of the orobiome have the same divisions in the spectrum of altitudinal belts, but they differ in typological diversity and the altitudinal limits of their distributions.Variations of the boundaries of the belts and sub-belts between the variants is more than 300 m for the lower limits of the Siberian pine and mountain taiga belts.This reflects the regional specificity in the structure of the altitudinal zonality of the vegetation cover in the orobiome.The Patom geographical variant is characterized by the most specificity in the altitudinal structure of the vegetation cover.Its diversity is connected with the relatively low altitudes of the highlands and the geographical location on the periphery of the area of active formation of floristic and coenotic diversity.
fig. 1. fragment of the map «The Biomes of Russia» (scale 1: 7 500 000) (2018).51.1, 51.2, 51.3 -geographic variants of the Kodar-Kalar orobiome fig. 3. Distribution of frequency of pine forests (1), larch forests (2), the Siberian pine forests (3) and shrub tundra (4) occurrence in the Kodar-Kalar orobiome by altitudes.Continuous lines are trends.Dashed lines are standard deviations from the mean altitudesThe bimodal distribution is noted for shrubby and herb tundra.The deviation from the normal distribution can be caused by two reasons.First, vegetation units on the map can be heterogeneous in botanical-geographical and ecologicalphytocoenotic terms due to a wide range fig. 5.The distribution of vegetation units (names -see table 2) of theKodar-Kalar orobiome (1) and its geographic variants: the North Baikal (2), the Patom (3), the Kodar-Kalar (4), ranked by average altitudes, and their standard deviations from the mean values The structure of the altitudinal zonality of the vegetation for the Kodar-Kalar orobiome and its geographic variants (by the weighted mean altitudes and their standard errors for the basic vegetation communities of altitudinal belts and sub-belts) larch forests sub-belt 685-967 715-1006 578-859 824-1046 IV.2.The larch-pine and firpine-spruce forests sub-belt 178-685 460-715 178-578 455-824 The lower half of the spectrum is occupied by the typologically diverse communities of the mountain-taiga belt.Here, fir-spruce (Picea obovata, Pinus sibirica, Abies sibirica Ledeb.) and larch (Larix sibirica Ledeb.)herbaceous, shrubby-moss forests of the Ural-Siberian complex of formations predominate in the lower periphery of the orobiome (the Patom variant).They have small values of the standard deviation and minor altitude amplitude, forming the lower sub-belt of the mountain taiga belt (180-580 m).Pine (Pinus sylvestris) and larch (Larix gmelinii)pine shrubbery-lichen forests are confined to intermountain depressions and low mountains (450-820 m).Boreal forests of the Eastern Siberian geographic and genetic complex of plant formations participate in the composition of the upper sub-belt, the largest variety of which is found in larch communities.Larch scrub (Betula divaricata Ledeb., B. exilis Sukaczev), rhododendron (Rhododendron dauricum L.), shrubby (Vaccinium uliginosum L., Ledum palustre L.) moss forests grow at altitudes of 690-970 m.Highlands are occupied by sub-tundra and tundra vegetation communities.Larch and spruce with Siberian dwarf pine (Pinus pumila), alder (Duschekia fruticosa (Rupr.)Pouzar) moss-lichen sparse forests occupy the lower part of the sub-tundra belt at heights of 970-1130 m.Fragments of birch (Betula lanata) are developed at altitudes of 1130-1330 m.Shrub, shrubby, moss-lichen tundra form a mountain tundra belt (1330-1900 m).Sparse fragments of the tundra community form the upper tundra belt (1900-3000 m).