ISSN 2079-0864, Biology Bulletin Reviews, 2017, Vol. 7, No. 3, pp. 229–237. © Pleiades Publishing, Ltd., 2017. Original Russian Text © N.B. Ermakov, A.V. Larionov, M.A. Polyakova, Yu.V. Plugatar, 2016, published in Zhurnal Obshchei Biologii, 2016, Vol. 77, No. 4, pp. 293–302.

Ecological Interpretation of Higher Units of Steppe Vegetation in the Mountains of Southern Middle Siberia by Quantitative Ordination N. B. Ermakova, *, A. V. Larionovb, **, M. A. Polyakovaa, *, and Yu. V. Plugatarc, *** aCentral

Siberian Botanical Garden, Siberian Branch, Russian Academy of Sciences, ul. Zolotodolinskaya 101, Novosibirsk, 630090 Russia b Lyceum Municipal Educational Institution, ul. Lermontova 12, Abakan, 655016 Russia cNikita Botanical Garden, settl. Nikita, Yalta, Republic of Crimea, 298648 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] Received May 12, 2015

Abstract⎯An ecological ordination model of higher units of steppe vegetation in the mountains of the southern Middle Siberia was created based on indirect ordination (detrended correspondence analysis) of 326 complete geobotanical descriptions and on a correlation analysis of the values of main axes with climatic, soilground, and geographical parameters. Ecological series of coenofloras of the steppe vegetation are observed in the space of the two first leading axes of ordination. They are oriented by climatic factors of the annual and seasonal precipitation amounts, temperature, oceanity–continentality, and substrate rockiness. A syntaxonomic interpretation of the observed ecological-geographical steppe types is given, and a hierarchy of higher classification units is substantiated from ecological positions. DOI: 10.1134/S2079086417030033

INTRODUCTION A deep understanding and modeling of the regularities of its ecological–biological and geographical organization are the basis for solving modern problems on the preservation of vegetation diversity. At present, a significant number of diverse portrait, cartographical, and descriptive models have been created for the territory of Siberia and Northern Eurasia; they reveal (with different degrees of accuracy) different aspects of the complex process of the development of spatial vegetation organization, which are mainly due to climatic factors (Box, 1981; Prentice et al., 1992; Tchebakova et al., 1994; Nazimova and Polikarpov, 1996; Ermakov et al., 2000; Ermakov, 2003; Tchebakova et al., 2003; Tchebakova and Parfenova, 2006; Nazimova et al., 2006; Krestov et al., 2009, 2010). However, almost all of them were developed for forests, while the developmental patterns of the steppe biome for geographically integral regions do not attract the attention of researchers of Northern and Central Asia, where a center of steppe-vegetation phytocenotic diversity is located and where large botanical-geographical boundaries pass. The problem of steppe vegetation classification underlies this scientific task. The low integrity and openness of the plant

communities requires the choice of a classification method that would result in the clearest establishment of relationships between the categories of vegetation of different sizes and a hierarchy of ecological and geographical factors. At present, the use of the indication potential of communities’ floristic composition to establish ecologically substantiated phytocenotic categories is considered to be one of the most promising methodologies; this was most completely reflected in the Braun–Blanquet approach. However, such important classification possibilities are not always realized, since the floristic composition is an indicator of states and processes in the community that differ in scale; this results in a controversial interpretation of the significance of some indication traits and, as a consequence, in the possibility of multiple syntaxonomic solutions during the creation of the classification hierarchy (Mirkin et al., 1989). This also concerns the recently created concept of steppe vegetation classification in Southern Siberia and Central Asia by the Braun–Blanquet method (Mirkin et al., 1985; Hilbig, 1990, 1996; Korolyuk, 2002; Makunina, 2006; Ermakov et al., 2009, 2012; Korolyuk and Makunina, 2009; Ermakov, 2012a, 2012b). In these works, the description of higher units and their diagnostic traits was mainly conducted based on the traditional table pro-

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rn ste an Say

0

Ri ve r

Ea

tau Ala tsk zne Ku 1 2

Ye nis ei

3 4 5

64 km

Western Sayan

Fig. 1. Placement of geobotanical descriptions in the study region. Designations: vegetation belts (1, forest–steppe belt; 2, steppe belt; 3, forest belt; 4, high mountain belt), 5, localization of geobotanical descriptions.

cessing of geobotanical descriptions and was accompanied by an empirical interpretation of the ecological-geographical properties of syntaxa. According to current requirements, the conceptual affirmation of syntaxonomic systems is accompanied by special quantitative studies on the establishment and testing of ecological-floristic integrity and indication traits of units and their hierarchical status. Multidimensional ordination analysis (detrended correspondence analysis, canonical correspondence analysis) based on the study of variation in the floristic composition of plant communities (observed along the ordination axes, interpreted as the manifestation of simple and complex gradients of ecological factors) serves as an efficient approach to the solution of these tasks. However, despite the quite long history of the use of these methods in phytocenology, their application in the study of ecological properties of the steppe vegetation in Southern Siberia and Central Asia was not widely used (including for substantiation of the results of classification). The goals of the present study were to perform ecological ordination modeling of the diversity of steppe communities in a geographically integral region (the Minusinsk intermountain basin and its mountain framework, Western Sayan and Kuznetskii Alatau (southern Middle Siberia)) based on geobotanical descriptions with a complete species composition and the parameters of leading ecological factors and to analyze the ecological content and floristic integrity of higher classification steppe categories described in this region by the Braun–Blanquet method. MATERIALS AND METHODS The use of the indication potential of communities’ species composition as a main trait in ordination vegetation modeling is the methodological basis of this study. In this regard, floristically complete geobotanical descriptions were used as a primary data for the

ordination, while syntaxonomic interpretation of the results was conducted based on the ecological–floristic Braun–Blanquet method (Westhoff and van der Maarel, 1973). Altogether, 326 complete geobotanical descriptions oriented along the series of geographical transects that cross all main geomorphological (and topographic) relief subdivisions from the mountain ranges of Kuznetsk Alatau and Western Sayan to the center of Minusinsk intermountain basin (Fig. 1), as well as bioclimatic facies (from humid cyclonic to insufficiently humid continental), were used (Nazimova et al., 1987). Geobotanical descriptions were conducted according to a standard method (Polevaya geobotanika, 1964; Westhoff and van der Maarel, 1973) at 100 m2 size areas. The seven-point Braun–Blanquet scale (r, +, 1, 2, 3, 4, and 5) was used to reflect the involvement of species in the descriptions. All geobotanical descriptions were entered in a standard Turboveg European package of phytosociological data (Hennekens, 1996). A methodical approach to the construction, explanation, and testing of the ordination model of ecological-geographical relationships of the steppe vegetation was implemented in stages. At the first stage, the qualitative ordination of the steppe vegetation coenofloras was carried out based on the complete “species composition × geobotanical descriptions” matrix by the DCA ordination method presented in the DECORANA package (Hill, 1979). The syntaxonomic interpretation of geobotanical descriptions grouped on the ordination axes was conducted based on the Braun–Blanquet system developed for Southern Siberia and Mongolia (Mirkin et al., 1985; Hilbig, 1990, 1996; Korolyuk, 2002; Makunina, 2006; Ermakov et al., 2009, 2012; Korolyuk and Makunina, 2009; Ermakov, 2012a, 2012b). At the second stage of the study, a quantitative determination of the ecological content of the steppevegetation higher subdivisions (detected according to the results of DCA ordination) was conducted. The analysis was performed in the statistical SPSS package via calculations of Pearson correlation coefficients for the leading DCA ordination axes and climatic, geographical (geographical latitude, longitude, height above the sea level), and soil-ground (habitat rockiness) indices obtained for each of 326 geobotanical descriptions. The passive projection of factor axes was constructed by means of multiple linear regression. For these purposes, a cartographic climatic model was created for the territory of mountains of southern Middle Siberia with special ArcGis-9.0 features, as well as digital relief model, weather station data (Spravochnik po klimatu SSSR, 1967), and the gradients of changes in the temperature and precipitation indices developed by climatologists for mountains of Southern Siberia (Polikarpov et al., 1986). The climatic model includes the following thematic layers: annual and average monthly air temperatures, differBIOLOGY BULLETIN REVIEWS

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ences in temperatures between the coldest (January) and the warmest (July) months, and precipitation (annual, monthly, during the warm (April–October) and cold (November–March) periods). The spatial resolution of the climatic model was determined by the digital relief model and is 30 m. The method of this model construction was described in the article by Chytrý et al. (2007). The construction of a climatic raster model made it possible to associate each geobotanical description with specific parameters of climatic factors by three geographical indices (latitude, longitude, and absolute height). To estimate the influence of the factor of soil-ground conditions, an index of crushed stone, gruss, and nude parent-rock covering (visually fixed under the field conditions) was used. The habitat rockiness (“petrophycity”) for each geobotanical description was estimated by the percentage of the involvement of the obligate petrophyte group. The nomenclature of syntaxonomic units is given according to the Code of Phytosociological Nomenclature (Weber et al., 2000), the taxonomic names of vascular plants are given according to Cherepanov (1995), and the mosses are named according to Ignatov and Afonina (1992). RESULTS AND DISCUSSION The created two-dimensional ordination model (Fig. 2) demonstrated the presence of eight clearly pronounced groups of geobotanical descriptions that represent steppe-vegetation coenofloras of different ranks that are oriented along the main variation axes (axes 1 and 2). According to the results of syntaxonomic analysis of complete series of descriptions, higher classification units (class, order, union, and subunion) were selected as basic categories during the consideration of the results of ordination. The list of units is given below: Festuco–Brometea Br.-Bl. et Tx. ex Soo 1947 class Stipetalia sibiricae Arbuzova et Zhitlukhina ex Korolyuk et Makunina 2001 order Aconito–Poion Korolyuk et Makunina 2001 union Veronico–Helictotrichion Korolyuk 2010 union Veronico incanae–Helictotrichenion desertori Korolyuk et Makunina 2006 subunion Youngio tenuifoliae–Helictotrichenion desertori Korolyuk et Makunina in Korolyuk 2006 subunion Cleistogenetea squarrosae Mirkin et al. 1992 class Festucetalia lenensis Mirkin in Gogoleva et al. 1987 order Festuco valesiacae–Caricion pediformis Ermakov, Larionov et Polyakova 2012 union Eritrichio pectinati–Selaginellion Ermakov, Chytry et Valachovič 2006 union Kitagawio baicalensis–Caricenion pediformis Korolyuk et Makunina in Makunina 2006 subunion BIOLOGY BULLETIN REVIEWS

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Kobresio filifoliae–Caricenion pediformis Larionov prov. subunion Kochio–Stipetalia krylovii Ermakov 2012 order Kochio–Stipion krylovii Ermakov 2012 union Stipion orientalis Korolyuk et Makunina 2009 union. The conducted analysis on the ecological content of the species composition of coenofloras of the vegetation units placed along axis 1 demonstrated the possibility of its interpretation as a gradient of climate humidity change. The gradient is spatially oriented from the more humid forest–steppe foothill of Western Sayan and Kuznetskii Alatau to the semiarid central part of Minusinsk basin as a result of the manifestation of the “rain barrier” and “rain shadow” effects typical for all large mountain systems. A sequential substitution of the four main ecological–geographical categories of the steppe vegetation (which correspond to the class–order–union ranks in syntaxonomic interpretation in the Braun–Blanquet system) is observed along the main ordination axis 1. Geobotanical descriptions of moderately mesophytic meadow steppes of Western Palearctic type (the Festuco–Brometea class represented by a single Stipetalia sibiricae order in the mountains of Middle Siberia) were located in the left part of the axis 1 in the range of values 0–2. It was divided into two unions (more humidified Aconito–Poion meadow steppes and less humidified Veronico–Helictotrichion meadow steppes). Communities of more xerophilous steppes of the Eastern Siberian–Central Asian geographical type (the Cleistogenetea squarrosae class) occupied the right part of the axis 1 in the range of values 2–5. Geobotanical descriptions of this class were divided along the axis into two groups by their order rank: moderately humid Festucetalia lenensis steppes and dry and desertified Kochio–Stipetalia krylovii steppes (Fig. 2). This clearly observed series of coenofloras corresponds to patterns of global sublongitudinal zonal–sector and subzonal substitution of the steppe vegetation. It is observed in the mountains of Southern Siberia, where meadow steppes of the Festuco–Brometea class are confined to the moderately humid cyclonic north macroslope of the Altai–Sayan mountain region (playing the role of the “rain barrier”). Steppes of the Cleistogenetea squarrosae class replace them as they move to the south in drier and continental internal regions of the southern macroslope of the Altai–Sayan mountain region (with a pronounced climatic “rain shadow” effect) and then in Mongolia. The detected patterns indicate an ecological originality and ecological–floristic integrity of the steppe-vegetation categories and provide the basis for bioclimatic interpretation of the content of higher units in the Braun–Blanquet system of the steppe biome in the mountains of the south of Middle Siberia. To confirm the results of the analysis of ecological patterns of syntaxon distribution along axis 1, the correlation coefficients of its values with a

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4

T_Ju Amp T_ann

DCA ordination axis 2

3

Lon

2 Syntaxa 1 2 3 4 5 6 7 8

Lat

St 1

T_Jan

Pwp A_h

P_ann Pcp 0

PC_r P_pet 1 0

1

2 3 DCA ordination axis 1

4

5

Fig. 2. DCA ordination diagram by axes 1 and 2 of descriptions of steppe communities in Minusinsk basin with passive projection of ecological and geographical parameters. The parameter values are increased along the direction of arrows. Syntaxa: 1, Aconito barbati–Poion transbaicalicae union; 2, Veronico incanae–Helictotrichenion desertorum subunion; 3, Youngio tenuifoliae–Helictotrichenion desertorum subunion; 4, Festuco valesiacae–Caricion pediformis union; 5, Kobresio filifoliae–Caricenion pediformis subunion; 6, Kitagawio baicalensis–Caricenion pediformis subunion; 7, Stipion orientalis union; 8, Kochio prostratae–Stipion krylovii union. Ecological and geographical parameters: St, slope steepness; A_h, absolute height; T_Ju, average temperature of the warmest month (July); T_Jan, average temperature of the coldest month (January); T_ann, average annual temperature; Amp, average annual temperature amplitude (July–January); Pwp, average precipitation amount in warm period (April–October); Pcp, average amount precipitation amount in cold period (November–March); P_ann, sum of precipitation per year; PC_r, soil rockiness (projective covering of gruss and nude of parent rock); P_pet, percentage of petrophytes; Lat, latitude; Lon, longitude.

number of climatic, soil-ground, and geographical parameters (presented in each geobotanical description) were calculated. It is obvious from the results given in the table that the largest values of the correlation coefficient of the axis 1 values are demonstrated with precipitation indices, and the association with the amount of precipitations is higher in the warm period than in the cold period. At the same time, the correlations of the axis 1 values with the temperature parameters were insignificant, which is explained by their smaller variability as compared with the amount of precipitation due to the relatively small latitude stretch of the study region and small range of absolute heights of the steppe vegetation distribution. This is also confirmed by the low correlation coefficients of the axis 1 values with geographical indices (latitude, longitude,

and absolute height). Such axis 1 values were demonstrated by high negative correlation values with substrate rockiness and the percentage of the involvement of petrophytic plants in the community associated with it (table). This is also indirectly associated with the main macroclimatic content of axis 1. An increase in the aridity and continentality of the climate in the mountains of Southern Siberia and Mongolia results not only in substitution of the background type of steppes of the Festuco-Brometea class on the Cleistogenetea squarrosae, but is also accompanied by more intensive erosional processes in the relief of the mountain–steppe landscapes. As a consequence, the communities of the steppes of Eastern Siberian–Central Asian type are characterized by high floristic diversity and activity of obligatory and optional petrophytes, BIOLOGY BULLETIN REVIEWS

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Pearson correlation coefficients of leading axis values with ecological and geographical parameters Axes 1

2

3

4

0.544

0.309

0.126

0.099

Axis eigenvalue

r

p

r

p

r

p

r

p

Average annual precipitations

–0.5551 <0.01

–0.5109 <0.01

0.151

0.01

–0.049

0.37

Average precipitation values in April–October

–0.5615 <0.01

–0.49

<0.01

0.0934

0.09

–0.03

0.59

Average precipitation values in November–March

–0.4838 <0.01

–0.496

<0.01

–0.2431 <0.01

–0.079

0.15

–0.061

0.28

0.09

0.11

0.04

–0.161

<0.01

–0.1569 <0.01

0.119

0.03

<0.01

0.006

0.29

0.38

–0.164

<0.01

Average annual temperature

0.2519 <0.01

0.3417 <0.01

–0.0845

Average July temperature

0.2252 <0.01

0.4919 <0.01

–0.2178 <0.01

Average January temperature

0.0057

0.92

–0.2474 <0.01

Amplitude of average temperatures of July and January (climate continentality)

0.078

0.16

0.3764 <0.01

Soil rockiness

0.3309 <0.01

–0.4757 <0.01

0.213

Percentage of petrophytes

0.4782 <0.01

–0.578

0.0485

<0.01

–0.1131

0.12

Slope steepness

–0.2825 <0.01

–0.2035 <0.01

–0.2971 <0.01

–0.021

0.70

Absolute height

–0.1818 <0.01

–0.3948 <0.01

0.1951 <0.01

–0.231

<0.01

Latitude

–0.0426

0.44

–0.0829

0.13

0.4561 <0.01

–0.484

<0.01

Longitude

–0.0549

0.32

0.1339

0.02

–0.1867 <0.01

0.246

<0.01

and petrophyte series are more typical for them as compared with Western Palearctic steppes. The DCA ordination axis 2 demonstrated a sequential substitution of the steppe-vegetation subdivisions of lower ranks (unions–subunions) that can be interpreted as ecological types of steppes relative to the character of the substrate of underlying rocks (Fig. 2, table). This is confirmed by the highest correlation coefficients of axis 2 values with the substrate rockiness indices and the percentage of petrophyte involvement. However, as opposed to axis 1, the manifestation of the substrate rockiness factor has a content fundamentally different in scale and reflects not the peculiarities indicated above in global differences of florogenesis of Eastern Siberian–Central Asian and Western Palearctic steppes but intralandscape differentiation of the steppe vegetation on regional petrophyte series (which develop depending on the processes of the relief formation). It was reflected in the syntaxonomic system at the level of unions–subunions in different classes and orders that were unidirectionally subdivided at axis 2 on ecological types of petroBIOLOGY BULLETIN REVIEWS

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phyte and nonpetrophyte steppes. The dry and desertified steppes of the Kochio–Stipetalia order at axis 2 are represented separately by unions of petrophyte steppes (Kochio–Stipion krylovii) and petrophyte steppes (Stipion orientalis). The Festucetalia lenensis order is also represented separately by two unions situated at axis 2: nonpetrophyte Festuco valesiacae–Caricion pediformis and petrophyte Eritrichio pectinati– Selaginellion. The latter was in turn subdivided into moderately petrophyte slope communities of the Kitagawio baicalensis–Caricenion pediformis subunion and strongly petrophyte communities of denuded peaks of mountains and ridges (Kobresio filifoliae– Caricenion pediformis). Similarly, the Veronico–Helictotrichion union in the composition of the Festuco— Brometea class Western Palearctic steppes was divided at axis 2 by the communities of nonpetrophyte Veronico incanae–Helictotrichenion desertori subunion and petrophyte Youngio tenuifoliae–Helictotrichenion desertori subunion. These results demonstrate the presence of ecologically corresponding petrophyte rows (series) of the steppe communities similarly ori-

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ented along axis 2 within each bioclimatic category (of the class–order syntaxonomic rank), and they also demonstrate the high importance of this factor for the development of mountain–steppe vegetation in general. The axis 2 values also demonstrated high correlations with the temperature indices (primarily with summer average monthly temperatures). The detected correlations of the temperature and substrate rockiness factors with axis 2, as well as their mutual negative correlation, have an explanation. The most petrophyte communities of the Kobresio filifoliae–Caricenion pediformis subunion in the study region occupy peaks of mountains and ridges with almost completely eroded soils, and these habitats are also the coldest due to larger absolute heights. The accumulation of transit loose substrate increases in the direction of the more heated foots of the slopes, and, correspondingly, the petrophycity of the steppe communities decreases. Therefore, the moderately thermophilic nonpetrophyte steppes of the Festuco valesiacae–Caricion pediformis union occupy the opposite position relative to petrophyte cryophytic Kobresio filifoliae–Caricenion pediformis steppes at axis 2. Axis 2 also reflects the total regional sequential substitution of moderately hygrophilous petrophyte–steppe vegetation of mountain ridges by drier and more heated communities on the well-developed soils of the bottom of Minusinsk intermountain basin. This pattern is confirmed by the high correlation of axis 2 values with the absolute height indices. A significant positive correlation between the axis 2 values with the climate oceanity–continentality factor is one more regularity manifested on this axis. It reflects an association of this factor with an increase in the diversity of petrophyte communities (as well as an increase in the role of petrophyte mountain–steppe species in them) during the transfer from the mountain framework to the intermountain basin center. A joint and unidirectional correlation of climate continentality with the heat supply and aridity factors is observed on axis 2. Here, one can see a more general pattern of the directed distribution of ecologically different types of steppe communities in accordance with an increase in the “rain shadow” effect from the mountain system (located in the west of Kuznetsk mountain system), which acts as a barrier on the path of the westward transfer of humid air masses. The ordination axis 2 should be considered a complex gradient of interrelated ecological factors that controls the development of steppe-vegetation diversity in the mountains of the southern Middle Siberia. An understanding of their role contributes to the development of the concept of the ecological content of syntaxonomic units of the middle-ranked steppes. Analysis of the distribution of geobotanical descriptions along axes 3 and 4 did not detect the presence of integral groups of descriptions (which correspond to phytocenotic categories) and provided no

sufficiently clear explanation of the observed variation of the floristic compositions. Since the significance coefficient for axes 3 and 4 was significantly lower than the coefficients for first two axes (table), they were excluded from the consideration. CONCLUSIONS The efficient reflection by syntaxa of different hierarchical levels of the most important ecological–geographical patterns of plant vegetation development is one of the most important assignments of the created vegetation classification systems; this opens possibilities for their use in the construction of topical and predictive ecological–phytocenotic models of different scales. The ordination method (realized in the present work) demonstrated a high degree of ecological–floristic integrity and informative value of syntaxonomic steppe-vegetation units of the Braun–Blanquet classification. This is a clear demonstration of the principle of hierarchical vegetation cover organization (developed by Sochava (1979)) in the obtained ordination diagram (Fig. 2); according to it, the first order associations are determined by the climate, while the second order associations by relief characteristics. Higher syntaxonomic categories of the steppe vegetation (classes and orders) obtained more precise bioclimatic substantiation on the factors of moisture availability, temperature, and oceanity–continentality. Along axis 1, bioclimatically caused substitution of syntaxonomic units of the steppe vegetation was primarily reflected at the level of the Festuco–Brometea (Western Palearctic type geographically associated with the residual effect of western Atlantic humidity transfer in the mountains of Southern Siberia) and Cleistogenetea squarrosae (Central Asian–Eastern Siberian geographical type developing under conditions of ultracontinental semiarid climate) classes (Korolyuk, 2002; Makunina, 2006; Ermakov et al., 2014). These global bioclimatic differences of two higher units of Eurasian steppe vegetation are determined by floristic criteria, namely, the ratio of different chorological groups of the species: on the one hand, the Euro-Siberian and Eurasian species prevailing in the Festuco–Brometea composition (Anemone sylvestris, Artemisia glauca, A. sericea, Astragalus danicus, Campanula glomerata, C. sibirica, Carex humilis, Festuca valesiaca, Filipendula stepposa, Phlomoides tuberosa, Fragaria viridis, Medicago falcata, Onobrychis arenaria, Phleum phleoides, Poa angustifolia, Plantago urvillei, Pimpinella saxifraga, Polygala comosa, Scabiosa ochroleuca, Seseli libanotis, Stipa capillata, S. pennata, S. zalesskii, Trommsdorfia maculata), on the other hand, Central Asian and those Eurasian species that have the main area and demonstrate the greatest activity in the Central Asian steppes of the Cleistogenetea squarrosae class (Artemisia frigida, Bupleurum bicaule, Caragana pygmaea, Cleistogenes squarrosa, Goniolimon speciosum, Heteropappus altaicus, Poa attenuata, P. botryoides, BIOLOGY BULLETIN REVIEWS

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Potentilla acaulis, Potentilla bifurca, Stipa krylovii). The obtained high correlations of the axis 1 values with the index of the precipitation amount demonstrate the different bioclimatic contents and principally significant floristic and ecological differences between the two zonally corresponding types of meadow steppes referred to the Stipetalia sibiricae (Southern Siberian meadow steppes of Western Palearctic type) and Festucetalia lenensis (Eastern Siberian–Central Asian meadow steppes) orders. Different aspects of the classification and geography of these two large ecological and botanical–geographical subdivisions of Eurasian meadow steppes were discussed in the literature long ago (Lavrenko et al., 1991; Korolyuk, 2002); however, they were still not represented as different categories in existing ordination models and legends of geobotanical maps created for different regions of the mountains of the south of Western and Middle Siberia (Lapshina, 1963; Kuminova et al., 1979, 1985; Tchebakova and Parfenova, 2000; Parfenova and Tchebakova, 2003). One of the reasons for this is that the mentioned thematic vegetation maps and models are based on physiognomic traits, while the communities of Southern Siberian meadow steppes of Western Palearctic type and Eastern Siberian–Central Asian meadow steppes, which are strongly differe floristically, are characterized by a high similarity of the structural–phytocenotic structure, the presence of common dominants, and similar landscape positions in the zone of area contact. The important ecological steppe-vegetation traits (which are reflected by syntaxonomic system at the level of unions–subunions) are demonstrated by parallel rows of ecological steppe types differing in the type of underlying rocks. These types are unidirectionally oriented toward axis 2 of the ordination model within the Festuco–Brometea and Cleistogenetea squarrosae classes. The detected large range of ecological–floristic variation in the communities of the petrophyte row of Central Asian steppes as compared with Western Palearctic–type steppes is caused by the prevalence of petrophyte xerophytes in them (which are evolutionarily associated with habitats affected by active erosional processes and are prevalent in semiarid mountain–steppe landscapes of Southern Siberia and Mongolia). In the obtained ordination model, this was confirmed by high indices of the positive correlations between the axis 2 values and oceanity–continentality factors, heat supply, and aridity. In a summary of the analysis of ecological patterns of the syntaxon distribution along the main ordination axes, it should be noted that these axes represent complex ecological gradients. Nevertheless, attempts to explain their content with consideration of the role of each of analyzed ecological factors in connection with the manifestation of other factors makes it possible to understand important functional characteristics of the establishment of the steppe-vegetation type. The observed ecological patterns of syntaxonomic steppe diversity in the obtained ordination model are BIOLOGY BULLETIN REVIEWS

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methodologically caused by the use of the indication potential of all species compositions of the communities; it reflects with a high degree of reliability their ecological properties. The formational approach (and the physiognomic approach based on it), which is frequently used in the modeling of ecological–geographical patterns of plant cover diversity, is “bound” to the ecological properties of one or a few species (dominants); this is a significant limitation of the indicator traits of the vegetation units. The created ordination model can be transformed in an ecological–phytocenotic correlation cartographic model of the steppe-vegetation type in the mountains of the southern Middle Siberia, since all of the units represented in it act as indicators of regional manifestation of climatic and soil-ground factors, correlate well with the orography and can be identified by direct and indirect traits on the space images. This is of great significance for an understanding of the functional patterns of steppe-vegetation organization, which act as a basis for the development of a strategy for its preservation, as well as the preparation of predictive models of its dynamics as a result of global environmental changes. ACKNOWLEDGMENTS The development of a methodical approach to modeling “vegetation–climate” associations was performed within and supported by the Russian Science Foundation, project no. 14-50-00079. The studies on ecological and syntaxonomic peculiarities of the development of the steppe vegetation in Khakassia were supported by the Russian Science Foundation (project no. 14-14-00453). REFERENCES Box, E.O., Macroclimate and plant forms: an introduction to predictive modeling in phytogeography, in Tasks for Vegetation Science, London: Dr. W. Junk, 1981, vol. 1. Cherepanov, S.K., Vascular Plants of Russia and Adjacent States (the Former USSR), Cambridge: Cambridge Univ. Press, 1995. Chytrý, M., Danihelka, J., Ermakov, N., et al., Plant species richness in continental southern Siberia: effects of pH and climate in the context of the species pool hypothesis, Global Ecol. Biogeogr., 2007, vol. 16, pp. 668–678. Ermakov, N.B., Raznoobrazie boreal’noi rastitel’nosti Severnoi Azii. Kontinental’nye gemiboreal’nye lesa: Klassifikatsiya i ordinatsiya (Diversity of Boreal Vegetation of the Northern Asia. Continental Hemiboreal Forests: Classification and Ordination), Novosibirsk: Sib. Otd., Ross. Akad. Nauk, 2003. Ermakov, N.B., Prodromus of Russian vegetation, in Sovremennoe sostoyanie osnovnykh kontseptsii nauki o rastitel’nosti (Modern Status of General Scientific Con-

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Translated by A. Barkhash