Floristic features and vegetation classification of the Hulun Buir Steppe in North China: Geography and climate-driven steppe diversification

Global Ecology and Conservation 20 (2019) e00741

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Original Research Article

Floristic features and vegetation classification of the Hulun Buir Steppe in North China: Geography and climate-driven steppe diversification Yuanjun Zhu, Dan Shan, Baizhu Wang, Zhongjie Shi, Xiaohui Yang*, Yanshu Liu** Institute of Desertification Studies, Chinese Academy of Forestry, Beijing, 100091, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 1 July 2019 Received in revised form 28 July 2019 Accepted 1 August 2019

This study aims to present a comprehensive description of the plant communities of the Hulun Buir Steppe based on floristically complete vegetation records as a baseline reference for future ecological and palaeoecological studies. We identify the main vegetation types in the Hulun Buir Steppe, provide their formal definitions and describe their species composition, habitat affinities and distributions. Floristic features (including floristic composition, life form and plant water ecotypes, floristic geographical elements) were also assessed. We recorded a total of 765 vascular plant taxa belonging to 68 families and 327 genera. The Hulun Buir Steppe indicates typical temperate steppe vegetation where the most frequent life form is hemicryptophytes with the maximum number of species. The most frequent water ecotype of Hulun Buir Steppe is typical-mesophytes. And the most frequent geographical element is the East Paleo-Arctic element. According to China
s resulted in vegetation classification system (China-VCS), the classification of 371 releve assignment into 31 formations (Form.) grouped into threeVegetation-types and eleven Vegetation-subtypes. Hulun Buir Steppe vegetation classifications were described for the first time based on complete floristic data and community survey data. Our conclusions show that among the 765 vascular plant taxa, the main plant group among all vascular plants in terms of species numbers comprises dicotyledons, followed by monocotyledons and pteridophyta, with gymnosperms demonstrating the lowest numbers. The life forms are dominated by hemicryptophytes, the water ecological type is dominated by typicalmesophytes, and the floristic geographical element is dominated by the East PalaeoArctic element. Plant community types are diverse and can be conceptualized as meadow steppe, typical steppe and desert steppe. The vegetation types of the Hulun Buir Steppe are mainly affected by geographic variables and climatic factors: the geographic variables are mainly affected by the change in precipitation caused by the longitude gradient, while the climatic factors are mainly affected by the East Asian winter monsoon caused by the Siberian High and the East Asian Summer Monsoon caused by the Western Pacific Subtropical High. In addition, the surface runoff caused by forest snowmelt and seasonal rainfall, as well as the distance from the Greater Khingan Mountains, also affect the distribution of the Hulun Buir Steppe vegetation. © 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Steppe vegetation Phytogeography Hulun buir steppe Vegetation classification

* Corresponding author. Institute of Desertification Studies, Chinese Academy of Forestry, Beijing, China. ** Corresponding author. Institute of Desertification Studies, Chinese Academy of Forestry, Beijing, China. E-mail addresses: [email protected] (Y. Zhu), [email protected] (D. Shan), [email protected] (B. Wang), [email protected] (Z. Shi), [email protected] (X. Yang), [email protected] (Y. Liu). https://doi.org/10.1016/j.gecco.2019.e00741 2351-9894/© 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

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1. Introduction As one of the largest vegetation type of the Eurasian continent, the Eurasian Steppe, which stretches between China in the east, southern Siberia, Kazakhstan, through Central and western Asia, and into Eastern Europe up to Hungary and Romania in the west (Werger and van Staalduinen, 2012; Nowak et al., 2018; Zhu et al., 2018), covers an extensive area (8e13 million km2) of the temperate arid and semiarid regions and is one of the most floristically diverse vegetation types occurring both in lowland and in the montane areas (Dengler et al., 2014; Willner et al., 2016). Since the last Ice Age, this large inland area underwent gradual and fluctuating change due to the encroachment of a sedentary civilization with intensified grazing and cropland cultivation (Bell-Fialkoff, 2000; Amitai and Biran, 2005). Additionally, drastic changes started from the beginning of the 20th century, when larger areas of the Eurasian Steppe became parts of communist states (the former Soviet Union, a part of eastern European countries and China), resulting in a series of ecological problems (Werger and van Staalduinen, 2012), which has attracted ecologists in research efforts encompassing decades (Borchardt et al., 2011; Miehe et al., 2011; Werger and van Staalduinen, 2012; Smelansky and Tishkov, 2012; Nowak et al., 2018). The available material from German and the Netherlands studies provides insight in the geobotany of the Mongolian forest-steppe (Hilbig and Knapp, 1983; Hilbig, 1987; Vries et al., 1996; Dulamsuren et al., 2005; Henrik and Karsten, 2007). Yet, these studies have concentrated on the mountainous areas of the Khentei ranges, southern Mongolian Gobi and the Hustain Nuruu area, and thus fail to cover the steppe vegetation in its full extent. As a part of the Eurasian Steppe, the Hulun Buir Steppe, located in Inner Mongolia of Northeast China, has remained relatively less disturbed in historical time; therefore, the original vegetation is well preserved and the biodiversity is abundant (Du et al., 2012; He et al., 2017). However, climate change and irrational human activities, such as fencing, mowing and overgrazing, in recent years have caused significant changes in vegetation of the Hulun Buir Steppe (Du et al., 2012; Zhang et al., 2013; Huhe et al., 2014; Liu et al., 2014); unfortunately, little is known about these changes. Vegetation classification is an essential tool to systematical description of vegetation and preparation of vegetation maps. It helps as well for understanding, managing and protecting biodiversity and ecosystem functions in large regions or countries (De C
aceres et al., 2015; Guo et al., 2018). Vegetation documentation and classification are central to biological conservation, from planning and inventory to direct resource management, and important in basic scientific research as a tool for organizing and interpreting ecological information and placing ecological research in an appropriate biophysical context (Michael et al., 2009). There has never been a greater need than now to systematic inventory, classification, and mapping the incredible diversity of vegetation and ecosystems on Earth, as land managers, conservationists, and policy makers are facing strong deterioration of landscape and vegetation impoverishment (Williams et al., 2000; Don et al., 2014). A consistent and comprehensive large-scale classification of vegetation units is an indispensable tool in ecological studies (e.g., diversity comparisons at community and ecosystem levels) for vegetation monitoring, implementing effective management and for developing conservation strategies and legislation (Mitchell, 2005; Willis and Birks, 2006; Beckage et al., 2008; Williams and Baker, 2011). China's territory is rich in vegetation types, with several climate zones from tropical to cold and large relief variations from the coast to the Himalayan Mountains (Chen et al., 2014). However, the methodologies and achievements in vegetation research in China, especially the China vegetation classification system (China-VCS), are little known to the world. In addition to the obvious reasons that all major achievements in vegetation research in China have been published in Chinese (Hou, 1960; ECVC , 1980; CENMN, 1985), another cause explaining the lack of sharing classification knowledge is that modern vegetation research in China started relatively late, and the early vegetation scientists adopted different approaches from different academic schools of vegetation science in their work (Hou, 1960; ECVC , 1980; Song, 2011). The China-VCS separates cultural vegetation from natural/semi-natural vegetation; for natural/semi-natural vegetation, it uses an integrated physiognomic-ecological-floristic-dynamic classification approach. It has eight hierarchical levels, i.e., Vegetation-type group (e.g. Forest), Vegetation-type (e.g. Deciduous needle leaved forest), Vegetation-subtype (e.g. Cold temperate deciduous needle leaved forest), Formation group (e.g. Larch forest), Formation (e.g. Larix gmelinii forest) and Sub-formation, as well as Association group (e.g. Larix gmelinii - Ledum palustre forest) and Association (e.g. Larix gmelinii - Ledum palustre - Vaccinium vitis-idaea - Sphagnum squarrosum forest) (Guo et al., 2018). In the past, an overview of the steppe vegetation of Inner Mongolia has been accomplished (CENMN, 1985), but the systematic classification of the Hulun Buir Steppe with detailed information on the species composition, physiognomic structure, distribution and coverage, has never been compiled. In this research, we defined the vegetation types of the Hulun Buir Steppe and analyzed the community characteristics of different vegetation types according to the China-VCS(Guo et al., 2018) based on a detailed and systematic vegetation survey. The main aims of our phytosociological survey were to address the following questions: (1) What is the classification of the steppe vegetation of the Hulun Buir Steppe and its distribution? (2) What is the species composition and physiognomy of the distinguished plant communities? And (3) What driving factors form the steppe structure and diversity? We anticipate these findings to provide a more precise and scientific delineation of the floristic features and vegetation classification of steppe types in the northeastern Mongolian Plateau, which can lay foundations for vegetation-related research in this special steppe.

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2. Methods 2.1. Study area The Hulun Buir Steppe is located between 47
050 -53
200 N and 115
310 e123
000 E, with a total area of 7.86  104 km2, width of 350 km from east to west, and length of 300 km from north to south. It lies east of the Ergun River, west of the Greater Khingan Range, south of the Gen River, north of the Khalkha River, and in the neighborhood of Mongolia and Russia, including the cities of Hailar, Manzhouli, New Barag Left Banner, New Barag Right Banner, Evenk Autonomous Banner, Old Barag Banner, and the south of Ergun and Yakeshi (CENMN, 1985; Zhang et al., 2011) (Fig. 1). The Hulun Buir Steppe comprises flat, vast and undulating high plains and includes from east to west three landscape types consisting of the low and medium hills of the west of the Greater Khingan Range, the high depression plains of Hulun Buir and the low hills of the west of Hulun Lake. The elevation is 600e750 m above sea level (Guo, 2004). The study area belongs to the temperate continental monsoon climate, which is hot and rainy in summer and cold and long in winter. The average annual temperature varies from 0 to 3
C, and the accumulated temperature above 10
C totals 1700e2300
C. The frost-free period ranges from 85 to 155 days. The temperature in the southwest is higher than in the northeast, with a sufficient sunshine period of 2650e3000 h year1. The mean annual precipitation is 250e500 mm, but it is uneven in spatial and temporal distribution. It decreases from the northeast to the southwest, and approximately 80% is concentrated between June and September. Therefore, the coupling between rainfall and temperature conditions in summer provides a better growing environment for the perennial and typical-mesophyte vegetation (Zhang et al., 2011; Huhe et al., 2014; Liu et al., 2014). 2.2. Data collection The vegetation was sampled phytocoenology in July and August of 2017. From the eastern end of the western foothills of
s were the Greater Khingan Mountains to the western end of the China-Mongolia border, four transects were set, and releve distributed almost evenly along the west-east longitude gradient, being sampled every 2e3 km, except in urban, disturbed areas, rivers and lakes. In total, 371 fixed sites were selected away from roads (>100 m) in homogeneous and natural steppe vegetation (Fig. 1-b). Within each site, three 1 m  1 m quadrats were selected randomly (the distance between the quadrats
, the total cover, cover abundance, density and height of the occurring vascular plant is more than 10 m), and in each releve
were averaged across the three quadrats (Fang species were recorded. The species cover, density and height at each releve et al., 2009). The hygrophyte and desert communities were excluded from this study because our study focus was on steppe vegetation. In addition, vegetation types, environmental data (latitude, longitude, altitude, aspect, slope angle, bedrock, topographical situation), and anthropogenic activities were recorded. A commercial GPS (Garmin 12 channel) was
. used to record the altitude and geographical position of each releve The analysis of flora characteristics was based on the total number of species including the collection of vascular plant specimens in the studied area, the investigation of phytosociological communities and the records in related literature (Zhao, 2012; ECFI, 1989e1998). Vascular plants were collected and identified in the laboratory. Plant nomenclature mainly followed Flora of China (Wu & Raven, 1994e2013), but recent taxonomic literature was also used to update some species names. Plant life forms were defined according to Raunkiǽr's classification (1934) based on the position of renewing buds in relation to the soil surface (phanerophytes, chamaephytes, hemicryptophytes, geophytes, annuals). Plant water ecotypes and floristic geographic elements of each species were defined according to Flora of China (Wu and Raven, 1994e2013) and Zhao's book (Zhao, 1987). Subsequently, the percentage of plant life forms, plant water ecotypes and floristic geographic elements in each interval were determined, and related diagrams were drawn (Fig. 2, Fig. 3). 2.3. Data analysis
s were analyzed in the JUICE6.5 program (Tichý, 2002). Modified TWlNSPAN (Hill, 1979; Role Data from all the releve cek et al., 2009) was used to classify plant communities based on the species composition. Diagnostic species were identified using the phi coefficient(F) as a fidelity measure (Chytrý & Tichy, 2003). Group size was standardized, and Fisher's exact test (p < 0.05) was applied. Species with a phi coefficient higher than 0.40 were considered diagnostic for a particular cluster. Diagnostic taxa for alliances were defined as those with a phi coefficient 0.15 in at least two clusters within this alliance. Species with a higher frequency than 50% were defined as constant, and those with a maximum cover value exceeding 30% were considered the dominant species of an individual cluster (plant community). The importance value (IV) data of each species were used for community classification using TWINSPAN. For translation of the TWINSPAN results into associations, we chose the highest division that still yielded floristically well-characterized terminal clusters with their own diagnostic species (Dengler et al., 2005; Michl et al., 2010). These terminal clusters were considered as associations or plant communities depending on the geographical range and certainty of the taxonomic status of the diagnostic species. During the division, the habitat profile and authors' field experience were used to identify comprehensive and ecologically interpretable classification results. For the vegetation type nomenclature, the China-VCS (Guo et al., 2018) was followed, and for descriptions of asso
s are given in the description of the discussed syntaxa. All mentioned syntaxa were ciations, the China-VCS. The type releve arranged into a syntaxonomic overview at the beginning of the description in the Results section.

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Fig. 1. Location of the Hulun Buir Steppe and distribution of sampling points. Note, a: The location of the study area in Mongolia Plateau, b: Distribution records of the sample sites.

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Fig. 2. Life-form spectrum and plant water ecotypes of Hulun Buir Steppe. Note, Ph: Phanerophytes, Ch: Chamaephytes, H: Hemicryptophytes, Cr: Cryptophytes, Th: Therophytes; Hy: Hygrophytes, HM: Hygro-mesophytes, TM: Typical-mesophytes, XM: Xero-mesophytes, MX: Meso-xerophytes, TX: Typical-xerophytes.

The species diversity indices were calculated as follows. The importance value (IV) of each species was calculated and used in the multivariate analysis of the communities. The importance value was calculated using the following formula (Zhang, 1995, 2004; Meng et al., 2012):

IV ¼

Relative coverage þ Relative height 200

Relative coverage/height refers to the proportion of one species accounting for the sum calculated for each plot individually. Four indices were chosen to estimate diversity: Species richness, Shannon-Wiener's Index, Pielou Index and Simpson Index, and IV of the species is used to calculate the biodiversity index (Whittaker, 1972; Ma, 1994; Spellerberg and Fedor, 2001; Fang et al., 2009). SPSS 21.0 (SPSS, Inc., Chicago, IL, USA) software was used for One-way Anova and linear regression analysis for statistical analysis in this paper. 3. Results

3.1. General floristic characteristics and floristic geographic elements 3.1.1. Floristic composition We recorded a total of 765 vascular plant taxa distributed among 68 families and 327 genera (Table 1). The main plant group among all vascular plants in terms of species numbers were dicotyledons, followed by monocotyledons. Pteridophyta

Fig. 3. Floristic geographic elements of Hulun Buir Steppe. Note, WS: World wide spread element, PaT: Pan-Temeperate element, PaA: Pan-Arctic element, PA: Palaeo-Arctic element, EPA: East Palaeo-Arctic element, SE: Siberia-East Asia element, ME: Mongolian Plateau-East Asia element, EA: East Asia element, PM: Palaeo-Mediterranean element, MA: Middle Asia element, M: Mongolian Plateau element, ES: Exotic species element.

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Table 1 Floristic composition of hulun buir steppe. Phyto-group

Families Percent of total Families Genera Percent of total Genera Species Percent of total Species

Pteridophyta Spermatophyte Gymnosperms Angiosperms Dicotyledons Monocotyledons Total vascular flora

3 1 57 7 68

4.35 1.45 84.06 10.14 e

3 1 261 64 327

0.91 0.30 79.33 19.45 e

6 1 613 148 765

0.78 0.13 79.82 19.27 e

were represented by 6 species in the Hulun Buir Steppe, all of which were herbaceous. The least numerous were the gymnosperms. The dominant families (more than 10 species) accounted for 81.51% of all species with 16 families, 248 genera and 626 species, although they made up only 23.53% of the total families (Table 2). There were 7 families with more than 30 species, including Compositae, Gramineae, Leguminosae, Rosaceae, Caryophyllaceae, Chenopodiaceae, Ranunculaceae; and there were 9 families with 11e26 species including Liliaceae, Brassicaceae, Polygonaceae, Lamiaceae, Scrophulariaceae, Cyperaceae, Apiaceae, Boraginaceae and Primulaceae. In contrast, there were 52 families with 1e10 species, making up 76.47% of the total families but contributing only 18.49% of the total flora. The dominant genera (more than 5 species) accounted for 27.84% of all species, with 20 genera and 213 species, although they made up only 23.53% of the total genera (Table 3). There were 5 genera with more than 15 species, and the most speciesrich genus was Artemisia with 24 species, followed by the genera Potentilla, Polygonum, Saussurea and Carex. There were 15 genera with 6e12 species, including Astragalus, Allium, Viola, Poa, Oxytropis, Rumex, Iris, Taraxacum, Vicia, Stellaria, Adenophora, Pedicularis, Geranium, Chenopodium, and Corispermum, making up 2.22% of the total genera and contributing 16.34% of the total species. There were 307 genera with 1e5 species, including 462 species and contributing 60.39% of the number of species but forming 93.88% of the total number of genera. 3.1.2. Life forms and plant water ecotypes The overall analysis of the life-form spectrum of the Hulun Buir Steppe indicated a typical temperate steppe vegetation, where the most frequent life form group was the hemicryptophytes with the maximum number of species, followed by therophytes, cryptophytes, phanerophytes, and chamaephytes (Fig. 2-a). The examined plants species belonged to 729 herbaceous plants, and 36 shrubs and subshrubs. The most abundant life form class was the hemicryptophytes (438 species), occupying a large space in terms of life form. The main species of hemicryptophytes were perennial herbs (excluding rhizomes/bulbous herbs). Of 765 plant species, 173 were therophytes; the predominance of therophytes indicated that the flora

Table 2 Species richness of the main vascular plant dominant families (more than 10 species). Families

Genera Percent of total Genera

Species Percent of total Species

Families

Genera Percent of total Genera

Species Percent of total Species

Compositae Gramineae Leguminosae Rosaceae Caryophyllaceae Chenopodiaceae Ranunculaceae Liliaceae Brassicaceae

49 39 17 14 11 15 14 9 16

138 83 54 43 34 33 33 26 26

Polygonaceae Lamiaceae Scrophulariaceae Cyperaceae Apiaceae Boraginaceae Primulaceae Total

4 14 11 7 11 10 5 248

26 24 24 21 15 14 11 626

14.89 11.85 5.17 4.26 3.34 4.56 4.26 2.74 4.86

17.97 10.81 7.03 5.60 4.43 4.30 4.30 3.39 3.39

1.22 4.26 3.34 2.13 3.34 3.04 1.52 75.38

3.39 3.13 3.13 2.73 1.95 1.82 1.43 81.51

Table 3 Species richness of the main vascular plant dominant genera (more than 5 species). Genera

Species

Percent of total Species

Genera

Species

Percent of total Species

Artemisia Potentilla Polygonum Saussurea Carex Astragalus Allium Viola Poa Oxytropis Rumex

24 19 15 15 15 12 12 10 9 9 8

3.14 2.48 1.96 1.96 1.96 1.57 1.57 1.31 1.18 1.18 1.05

Iris Taraxacum Vicia Stellaria Adenophora Pedicularis Geranium Chenopodium Corispermum Total

8 8 8 8 7 7 7 6 6 213

1.05 1.05 1.05 1.05 0.92 0.92 0.92 0.78 0.78 27.73

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of the commune of the Hulun Buir Steppe was highly composed of annual and biennial species and also indicated the adjustment of the flora to water balance. The cryptophytes made up 118 species, constituting 15.42% of the total population of the flora of the Hulun Buir Steppe; these plants included most of the Liliaceae family, as well as some rhizomes and bulbous perennial herbs. In contrast, chamaephytes and phanerophytes only composed 36 species, together constituting 4.71% of the total flora of the Hulun Buir Steppe. Unlike the North American prairie or tropical savannas, there were no trees on the Eurasian Steppe, so the species of chamaephytes and phanerophytes only composed a few shrubs and subshrubs. Our results revealed the predominance of hemicryptophytes and therophytes as the most important populations of flora on the Hulun Buir Steppe. Plant ecotypes could reflect the adaptability of plants to different environments (Ma and Liu, 2007). The study of the relationship between plants and water helps to understand geographical environment characteristics and the adaptability of plants (Zhang et al., 2007). The overall analysis of the plant water ecotypes of the Hulun Buir Steppe indicated that the most frequent water ecotype were the typical-mesophytes with a maximum number of species, followed by typical-xerophytes, meso-xerophytes and xero-mesophytes (Fig. 2-b). The explored plant species belonged to 540 xerophytes (including typical mesophytes, xero-mesophytes and hygro-mesophytes), 198 xerophytes (including typical-xerophytes and mesoxerophytes) and 27 hygrophytes. The most dominant water ecotype class was the typical-mesophytes, occupying the largest space with regard to water ecotypes. The main species of typical-mesophytes were mainly distributed in the central and eastern parts of the Hulun Buir Steppe. The typical-xerophytes forming the second most abundant water ecotype group were concentrated in the western parts of the Hulun Buir Steppe. There were 76 species and 63 species of meso-xerophytes and xero-mesophytes, respectively, and these 2 water ecotype species were mainly distributed in the central part of the Hulun Buir Steppe. The other 2 water ecotypes (hygro-mesophytes and hygrophytes), with 40 and 27 species, respectively, were mainly distributed in the eastern parts of the Hulun Buir Steppe and the transition zone of the forest and grassland at the western foot of the Greater Khingan Range. Our results revealed the predominance of typical-mesophytes and typicalxerophytesas the most important populations representing the water ecotype group of the Hulun Buir Steppe. This result also indicated that the distribution of the plants of the Hulun Buir Steppe was mainly affected by longitude, i.e., it was greatly affected by rainfall. 3.1.3. Floristic geographical elements The distribution types or floristic geographical elements are an important basis for studying the phylogenetic classification of vegetation, vegetation regionalization, natural geographical regionalization and regional natural geography, and the floristic geographical elements at the species-level are the most basic data for studying the nature and characteristics of flora, which is of great significance (Willis, 1985). The overall analysis of the floristic geographical elements of the Hulun Buir Steppe indicated that the most frequent geographical element group was the East Paleo-Arctic element with the maximum number of species, followed by the PaleoArctic element, East Asia element, Pan-Arctic element, and Siberia-East Asia element; other elements such as the Middle Asia element, Mongolian Plateau-East Asia element, Mongolian Plateau element, Worldwide spread element, PaleoMediterranean element, Pan-Temperate element and Exotic species element did not play important roles in the flora of the Hulun Buir Steppe. In the flora of the Hulun Buir Steppe, patterns of seed plant distribution of the flora at the species level are enumerated in Fig. 3. The species with an East Paleo-Arctic element distribution, such as Potentilla acaulis, Astragalus scaberrimus, Erodium stephanianum, Thymus mongolicus, Carex pediformis, and Iris dichotoma, etc., showed the highest percentage among all distribution types, contributing 24.84% to the flora. Species with a Palaeo-Arctic element distribution, such as Dianthus chinensis, Dracocephalum moldavica, Phlomis tuberosa, Plantago media, Bromus inermis, Saussurea amara, Geranium pretense and Euphorbia humifusa, etc., contributed 15.69% to the flora. Species with an East Asia element in the Hulun Buir Steppe distribution, contributing 15.42%, included Pulsatilla chinensis, Euphorbia esula, Platycodon grandiflorum, Anemarrhena asphodeloides, Tragus mongolorum, and Chrysanthemum naktongense, among others. These findings also indicate that the flora of the Hulun Buir Steppe is closely related to the flora of East Asia. The species with a Pan-Arctic element distribution, such as Equisetum ramosissimum, Equisetum pratense, Salsola collina, Cerastium arvense, Draba nemorosa, Geum aleppicum, Sanguisorba officinalis, and Carex duriuscula, among others, contributed 14.38% of the flora diversity. Species with a Siberia-East Asia element distribution included Patrinia scabiosaefolia, Artemisia lavandulaefolia, Leibnitzia anandria, Taraxacum borealisinense, Filipendula palmata, and Corispermum sibiricum, among others, contributing 12.29% of the flora diversity. In total, species with a temperate distribution (including the Pan-Arctic element, Palaeo-Arctic element, East Palaeo-Arctic element and SiberiaEast Asia element) comprised 67.19% of the total diversity of the Hulun Buir Steppe flora. The predominance of temperate elements indicates that the flora of the commune of the Hulun Buir Steppe has long been highly adapted to temperate climatic conditions. The species with Eurasian Steppe elements (including Mongolian Plateau-East Asia element, Middle Asia element and Mongolian Plateau element) contributed 11.37% of the total species. Although the number of species in this part was not dominant, many of them were dominant species ofthe Hulun Buir Steppe community, such as Stipa grandis, Stipa sareptana var. krylovii, Cleistogenes squarrosa, Ephedra sinica, and Caragana microphylla. Therefore, this geographical element group plays an important role in the composition and structure of the Hulun Buir Steppe community. The core group of species contributing to the data set was plants that were adapted to extensive grazing. The contribution of plants with an ecological optimum in other vegetation types, mainly in dry meadows, screes, rock habitats, ruderal and segetal vegetation, xerophytic shrubs, tall forbs, humid pastures, semi-deserts or even deserts, was negligible. Additionally, many species were also of great ecological significance. For example, Corispermum and Salsola plants in Chenopodiaceae were

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widely distributed on steppe and sandy land in the central and western part of the Hulun Buir Steppe. Allium polyrhizum in Liliaceae, Nitraria sibirica in Nitrariaceae, Stipa tianschanica var. klemenzii in Poaceae and Caragana stenophylla in Fabaceae are important constructive plants for desert steppe vegetation; Kalidium foliatum, Suaeda glauca in Chenopodiaceae and Glaux maritima in Primulaceae are constructive species for the salt steppe; and some species of Corispermum, Setaria and Salsola are vital pioneers on mobile sand dunes due to their resistance to drought and sand burial in sandy steppe regions (CENMN, 1985; Zhu et al., 2018; Li et al., 2018).

3.2. Classification and characteristics of the Hulun Buir Steppe communities 3.2.1. Classification of the Hulun Buir Steppe communities
s that were well-defined in terms of species In the Hulun Buir Steppe, our classification analysis detected 371releve
s was assigned to 31 formations (Form.) based on the fidelity (the phi composition. The classification of 371 synoptic releve
s (Fig. 4, Table 4), and these formations could be grouped into three ecologically coefficient values) of each species in the releve and biogeographically plausible (interpretable) Vegetation-types and eleven Vegetation-subtypes at a higher hierarchical level. For the superior syntaxonomic ranks, we selected levels within the cluster tree that yielded floristically unique and ecologically interpretable units. In this way, each syntaxonomic level corresponded to a horizontal plane in the dendrogram (Fig. 4). As our research is pioneering in this study area, we did not apply any refinement in the classification by moving some
s between clusters. We justify this approach owing to insufficient field experience needed to identify atypical or releve fragmentary stands. In the Hulun Buir steppe vegetation-type group, the protocols and criteria used to define vegetationtypes are the dominant life form (growth form) and community physiognomy (ECVC , 1980; Guo et al., 2018). We interpreted the three cluster levels as vegetation-types, including the following. (1) The meadow steppe appearing on the easternmost part of the Hulun Buir Steppe and forest-steppe belt at the western foot of the Great Khingan Mountains. The meadow steppe is the most humid type of steppe, and it is also a steppe type that transits from steppe to meadow. It is mainly composed of typical mesophyte and mesoxerophytes low-temperature herbs of perennials, but it also contains a considerable number of wide-range xerophytes and typical xerophytes. (2)The typical steppe appearing on the central and eastern part of the Hulun Buir Steppe: The typical steppe is the most basic type of grassland, so it is also the most widely distributed type of grassland. This type of grassland is mainly composed of perennially typical xerophytic and wide-range xerophytic lowtemperature herbaceous plant, but xerophytic semishrub plants are also present as one of the dominant components of the typical steppe community. (3)The desert steppe appearing on the westernmost part of the Hulun Buir Steppe: The desert steppe is a steppe type that transits from steppe to desert, so it is also the most arid steppe type. The main plant ecological


s in Hulun Buir Steppe. Note, the figures on the dotted line and Fig. 4. The dendrogram of the community classification system for the whole data set of 371 releve at the bottom are the cluster numbers, the assignment of phytosociological ranks is indicated by horizontal dotted lines. The cluster numbers are shown in Table 4.

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Table 4 Thevegetation types classification systemof Hulun Buir Steppe. Classification of Hulun Buir Steppe vegetation units 1. Meadow Steppe 1.1 Bunch grass Meadow Steppe 1.1.1 Form. Stipa baicalensis 1.1.2 Form. Poa pratensis 1.2 Rhizome grass Meadow Steppe 1.2.1 Form. Leymus chinensis-mesophyte 1.2.2 Form. Other Rhizome grass 1.3 Forb Meadow Steppe 1.3.1 Form. Carex pediformis-mesophyte 1.3.2 Form. Bupleurum scorzonerifolium 1.3.3 Form. Potentilla tanacetifolia-mesophyte 1.3.4 Form. Filifolium sibiricum 1.4 Semishrub Meadow Steppe 1.4.1 Form. Caragana microphylla-mesophyte 2. Typical Steppe 2.1 Bunch grass Typical Steppe 2.1.1 Form. Stipa grandis 2.1.2 Form. Stipa sareptana var. krylovii 2.1.3 Form. Cleistogenes squarrosa 2.1.4 Form. Koeleria cristata 2.1.5 Form. Agropyron cristatum 2.1.6 Form. Agropyron desertorum 2.2 Rhizome grass Typical Steppe

2.2.1 Form. Leymus chinensis-xerophytism 2.3 Forbs Typical Steppe 2.3.1 Form. Carex duriuscula 2.3.2 Form. Carex pediformis-xerophytism 2.3.3 Form. Allium bidentatum 2.3.4 Form. Allium ramosum 2.3.5 Form. Potentilla acaulis 2.3.6 Form. Potentilla tanacetifolia-xerophytism 2.3.7 Form. Other Forbs 2.4 Semishrub Typical Steppe 2.4.1 Form. Thymus mongolicus 2.4.2 Form. Artemisia frigida 2.4.3 Form. Caragana microphylla-xerophytism 2.4.4 Form. Caragana stenophylla-typical 2.4.5 Form. Ephedra sinica 3. Desert Steppe 3.1 Bunch grass Desert Steppe 3.1.1 Form. Stipa tianschanica var. klemenzii 3.2 Forb Desert Steppe 3.2.1 Form. Allium polyrhizum 3.3 Semishrub Desert Steppe 3.3.1 Form. Caragana stenophylla

types of this steppe are typical perennial xerophytic herbs and a considerable number of xerophytic semishrub plants. The eleven-cluster level as vegetation-subtypes included the following: (1.1) Bunch grass Meadow Steppe, (1.2) Rhizome grass Meadow Steppe, (1.3) Forb Meadow Steppe, (1.4) Semishrub Meadow Steppe, (2.1)Bunch grass Typical Steppe, (2.2) Rhizome grass Typical Steppe, (2.3) Forbs Typical Steppe, (2.4) Semishrub Typical Steppe, (3.1) Bunch grass Desert Steppe, (3.2) Forb Desert Steppe, (3.3) Semishrub Typical Steppe. The community physiognomy of different vegetation-subtypes in the Hulun Buir Steppe is shown in Fig. 5. For the cluster level of formations, the vegetation-type classification system of the Hulun Buir Steppe is shown in Table 4.

Fig. 5. The community physiognomy of different vegetation-subtypes in Hulun Buir Steppe.

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Y. Zhu et al. / Global Ecology and Conservation 20 (2019) e00741

Each syntaxon (vegetation-subtypes and formations) is characterized by its number and name from the dendrogram of the community classification system (Fig. 4), the vegetation-type classification table (Table 4), community characteristics (herb layer cover, height of herb layer, above-ground biomass, dissimilarity) and diversity index (Fig. 6) and the synoptic table of three vegetation types (Tables 5e7).

3.3. Plant community description of Hulun Buir Steppe

3.3.1. Meadow steppe 3.3.1.1. Bunch grass meadow steppe. This vegetation-subtype included 2 formations, which were mainly composed of perennial tufted mesophyte bunch grasses. The main edificator species were Stipa baicalensis and Poa pratensis. During the research, many plots of the vegetation-subtypes were recorded on the eastern plains and low-mountain area of the Greater Khingan Mountains in the Hulun Buir Steppe. The community physiognomy of this vegetation-subtype is shown in Fig. 5(1.1). The plots with these edificator species occurred on grassland soil and mountain soil with the lowest average cover of herb layer and the lowest Pielou index among all meadow steppe vegetation-subtypes (Fig. 6). 3.3.1.1.1. Form. Stipa baicalensis. Diagnostic species: Stipa baicalensis. Constant species:Stipa baicalensis, Astragalus melilotoides, Koeleria cristata, Leymus chinensis, Cleistogenes squarrosa. Formation Stipa baicalensis is the most important herbosa community steppe type of the zonal meadow steppe, and it is a peculiar aboriginal type in the eastern part of the Eurasian steppe. This type of steppe is widely distributed along the foothills of the two sides of the Greater Khingan Mountains. Stipa baicalensis steppe is located in low-temperature regions of the semiarid and subhumid zones where the annual precipitation is 350e450 mm and the rainfall in July is generally over 100 mm in Hulun Buir. The mean height of Stipa baicalensis in the meadow steppe can reach 50e80 cm. The mean vegetation height was 14.02 cm. The mean cover of the herb layer was 41%. Species numbers per m2 plot ranged from 7 to 30, with a
, and the total number of species in the formation was 67. The most frequent species in this mean of 22 species per releve community included Stipa baicalensis, Astragalus melilotoides, Poa pratensis, Koeleria cristata, Allium bidentatum, Leymus chinensis, and Cleistogenes squarrosa. Other plant species in this formation were from the Achnatherum, Geranium, and Galium. 3.3.1.1.2. Form. Poa pratensis. Diagnostic species: Poa pratensis, Iris typhifolia, Stellaria media Constant species: Poa pratensis, Iris typhifolia, Stellaria media, Leymus chinensis, Gerbera anandria, Gypsophila davurica. Formation Poa pratensis is an important type of representative formations of the meadow steppe. Poa pratensis is a kind of perennial mesogenous bunch grass, with a mean height that can reach 50e90 cm. The mean vegetation height was 11.66 cm. The mean cover of the herb layer was 63%. Species numbers per m2 plot ranged from 21 to 23, with a mean of 23 species per
, and the total number of species in the formation was 36. The most frequent species in this community included Poa releve pratensis, Iris typhifolia, Stellaria media, Carex duriuscula, Potentilla bifurca, Leymus chinensis, Allium bidentatum, Gerbera anandria, and Gypsophila davurica. Other plant species in this formation were from the Chenopodium, Artemisia, Cleistogenes, and Astragalus. 3.3.1.2. Rhizome grass meadow steppe. This vegetation subtype included 2 formations that were mainly composed of perennial mesophyte rhizome grass, and the main edificator species are Leymus chinensis and other rhizome grasses. During the research, many plots of the vegetation subtype were recorded on the eastern plains and low-mountain areas of the Greater Khingan Mountains in the Hulun Buir Steppe. The community physiognomy of this vegetation-subtype is shown in Fig. 5(1.2). The plots with these edificator species occurred on the grassland soil and mountain soil, with the lowest average height of herb layer and the lowest Shannon-Weiner index and Simpson index among all meadow steppe vegetation subtypes (Fig. 6). 3.3.1.2.1. Form. Leymus chinensis-mesophyte. Diagnostic species: Leymus chinensis. Constant species: Leymus chinensis, Carex duriuscula, Poa pratensis, Stipa baicalensis, Heteropappus altaicus, Achnatherum sibiricum. In the Hulun Buir Steppe, we divided Leymus chinensis steppe into two formations according to the community characteristics and distribution. One type belonged to a meadow steppe, representing a type of Leymus chinensis steppe community mainly composed of mesophyte species and mainly distributed in the meadow steppe belt at the western foot of the Greater Khingan Mountains. The other type belonged to a typical steppe, representing a type of Leymus chinensis steppe community mainly composed of xerophyte species, which is similar to the community characteristics of Stipa steppe in a typical steppe region. Here we analysis formation Leymus chinensis in a meadow steppe. The natural distribution belt of this formation is wide, and it is the largest steppe type in size in the forest-steppe belt of the Greater Khingan Mountains in the Hulun Buir Steppe. The differences in moisture conditions and the soil salt regime are important ecological elements differentiating the types of Form. Leymus chinensis-mesophyte. It showed a well-developed zonal habitat and was the most developed steppe community in this habitat. The mean vegetation height was 11.99 cm. The mean cover of the herb layer was 51%. Species
, and the total number of species in the fornumbers per m2 plot ranged from 9 to 37, with a mean of 19 species per releve mation was 87. The most frequent species in this community included Leymus chinensis, Carex duriuscula, Poa pratensis, Stipa

Y. Zhu et al. / Global Ecology and Conservation 20 (2019) e00741

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Fig. 6. Box-whisker plots for cover of herb layer, height of herb layer, above-ground biomass, dissimilarity, richness (number of species per plot), ShannonWeiner index, Simpson index and Pielou index of different vegetation-subtypes.

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Table 5 Synoptic table of Meadow Steppe in Hulun Buir Steppe. The phi coefficient values (in superscript) in the table are multiplied by 100 and only shown when positive. Main values are species frequencies (in percentages). Only diagnostic taxa (phi  0.20) and species with frequency higher than 20% in the whole data set are shown. Vegetation-type

1. Meadow Steppe

Vegetation-subtype

1.1

Formation
s/species No. of total releve Mean vegetation cover (%) Mean vegetation height (cm) Stipa baicalensis Astragalus melilotoides Koeleria cristata Poa pratensis Iris typhifolia Stellaria media Gerbera anandria Gypsophila davurica Leymus chinensis Carex duriuscula Achnatherum sibiricum Heteropappus altaicus Bromus inermis Calamagrostis epigeios Sphallerocarpus gracilis Saussurea amara Carex pediformis Hemerocallis fulva Lilium dauricum Vicia cracca Geranium pratense Galium verum Bupleurum scorzonerifolium Asparagus schoberioides Haplophyllum dauricum Agropyron cristatum Potentilla tanacetifolia Glaux maritima Halerpestes ruthenica Olgaea lomonosowii Sanguisorba officinalis Filifolium sibiricum Geranium sibiricum Hordeum vulgare Caragana microphylla Hieracium umbellatum Gueldenstaedtia stenophylla Orostachys fimbriatus Medicago sativa Iris tenuifolia Iris lactea var. chinensis

1.1.1 12/67 41.47 14.02 8347 5834 8322.7 83— 17— . . . 9222 67— 50— 33— . . . . 33— . . . 8— 17— 50— . . 17— 50— . . . . 17— . . . . 8— . . . 8—

1.2 1.1.2 2/36 63.17 11.66 50— . . 10070.1 10057.5 5069.9 5069.9 5069.9 10029 100— . 50— . 50— . . . . . . . . . . . . 50— . . . . 50— . . . . . . . . .

1.2.1 18/87 50.56 11.99 6120.1 11— 39— 6123.8 22— . . . 10062 8913.5 3320.8 7822 . . . 33— 33— . . . 6— 22— 50— 6— . 17— 44— . . . 11— 11— . . 6— . 6— 6— 6— . 11—

1.3 1.2.2 2/47 70.00 13.70 . . . . . . . . 10021.7 50— . 50— 5072.2 5060.1 5059.9 5020.2 10024.9 . . . 50— 50— 50— . . 50— 100— . . . . . . . . . . . . . 50—

1.3.1 21/122 59.86 16.02 48— 5— 48— 62— 29— . . . 71— 38— 38— 14— 298.1 10— . 19— 10052.6 2447.9 1942.8 4837.7 3821.5 6220 71— . 10— 6213.6 57— . . . 4325.3 19— . . 10— 10— . . . 10— 19—

1.4 1.3.2 6/63 55.17 14.79 8320.1 50— 50— 67— . . . . 100— 67— 17— 50— . . . 17— 33— . . . . 17— 10077.3 5060.8 3341.7 8324.6 67— . . . . 33— . . 17— . . 17— 17— 33— 17—

1.3.3 3/23 64.33 8.34 33— . . 10030.2 . . . . 100— 67— . . 6735.9 . . 67— 33— . . . . . . . . 33— 10085 10045 3356.8 3356.8 . . . . . . . . . . 33—

1.3.4 2/31 64.33 16.41 . . 50— 5023 . . . . 10024.9 . 50— . . . . 50— 100— . . . . . . . . 50— 50— . . . 5065.5 5052.6 5049.9 5049.9 . . . . . . .

1.4.1 3/44 47.78 18.62 67— . 67— 100— . . . . 100— 67— 6722.7 33— . . . . 33— . . 33— . 67— 67— . . . 67— . . . . 67— . . 10072.4 6768.3 6764 6757.5 6757.5 6746.7 10042.2

baicalensis, Artemisia scoparia, Heteropappus altaicus, and Cleistogenes squarrosa. Other plant species in this formation were from the Chenopodium, Artemisia, Cleistogenes, and Astragalus. 3.3.1.2.2. Form. Other rhizome grass. Diagnostic species: Bromus inermis, Calamagrostis epigeios, Sphallerocarpus gracilis. Constant species: Bromus inermis, Calamagrostis epigeios, Sphallerocarpus gracilis, Carex pediformis, Saussurea amara, Leymus chinensis. The edificator species formingother rhizome grasses included Bromus inermis and Calamagrostis epigeios, which is a azonal vegetation type of the meadow steppe in northeast hulun buir grassland. The mean height of Bromus inermis in the rhizome grass meadow steppe is taller, reaching reach 50e120 cm, and the mean height of Thalictrum petaloideum can reach 20e80 cm. The mean vegetation height was 13.70 cm. The mean cover of the herb layer was 70%. Species numbers per m2 plot
, and the total number of species in the formation was 47. The most ranged from 22 to 31, with a mean of 26 species per releve frequent species in this community included Bromus inermis, Calamagrostis epigeios, Sphallerocarpus gracilis, Carex pediformis, Potentilla bifurca, Saussurea amara, Artemisia scoparia, Leymus chinensis, and Astragalus scaberrimus. Other plant species in this formation were from the Tragus, Lappula, Hordeum, and Potentilla tanacetifolia.

Table 6 Synoptic table of Typical Steppe in Hulun Buir Steppe.The meaningsof contents in the table are the same as those in Table 4. 2. Typical Steppe

Vegetation-subtype

2.1

Formation
s/species No. of total releve Mean vegetation cover (%) Mean vegetation height (cm) Stipa grandis Medicago ruthenica Stipa sareptana var. krylovii Lepidium apetalum Cleistogenes squarrosa Pulsatilla turczaninovii Gueldenstaedtia stenophylla Hieracium umbellatum Medicago sativa Allium tenuissimum Setaria viridis Koeleria cristata Euphorbia fischeriana Stipa baicalensis Polygonum lapathifolium Sanguisorba officinalis Galium boreale Astragalus galactites Geum aleppicum Hemerocallis fulva Artemisia annua Vicia amoena Agropyron cristatum Lespedeza davurica Agropyron desertorum Filifolium sibiricum Artemisia lavandulaefolia Leymus chinensis Polygonum sibiricum Polygonum thunbergii Youngia tenuicaulis Carex duriuscula Plantago asiatica Chenopodium album Artemisia tanacetifolia Taraxacum borealisinense Taraxacum mongolicum Potentilla bifurca var. major Potentilla tanacetifolia Potentilla bifurca Carex pediformis Allium bidentatum Convolvulus ammannii Allium senescens Allium ramosum Artemisia scoparia

2.1.1 51/82 56.33 21.69 10052.6 2023.6 . 2— 8822.8 6— 8— . . 45— 2— 29— . . . . . . . . . . 76— . . 6— . 7817.7 . . 4— 73— . 27— 2— 4— 12— 6— 4— 37— 24— 25— 6— 24— 18— 51—

2.1.2 9/43 33.44 18.68 22— . 8985.2 3350.4 7820.5 . . . . 7810.6 11— 11— . . . . . . . . . . 10020.1 . . . . 33— . . . 5621.1 . 67— . . . . . 33— 33— 33— . . 11— 44—

2.1.3 4/40 45.25 12.08 100— . . . 10042.5 5056.1 5053 2549.1 2549.1 10021.6 5031.5 25— . . . . . . . . . 25— 50— . . 25— . 50— . . . 75— . 50— . . . 25— . 25— 50— . . 50— 50— 100—

2.1.4 2/31 51.67 22.06 . . . . 50— . . . . 50— . 10079.3 100100 10079.3 5069.9 5069.9 5069.9 5069.9 5069.9 5069.9 5059 5036.6 . . . . 5025.8 5020.9 . . . . . . . . . . 50— 50— 50— . . . 50— .

2.1.5 23/64 34.18 10.73 5721.2 9— 4— . 78— . . . . 17— 225.6 43— . 13— . . . . . . 4— . 10052.8 1740.9 . 3520.1 . 52— . . 4— 78— . 43— 4— . 17— 4— . 13— 13— 13— . 17— 22— 43—

2.1.6 2/17 35.50 18.23 50— . . . . . . . . 50— . 10021.3 . . . . . . . . . . . . 100100 10048.1 5025.8 . . . . 50— . 10010.2 . . . . . . 10021.4 . . 50— . 100—

2.2

2.3

2.2.1 39/77 46.10 10.22 4432.1 15 . 15— 46— 5 . . . 10— 5— 28— . . . . . . . . 3— . 28— 3— . 5— 8— 6755.8 1025.3 522.2 1318.1 4638.4 . 23— 5— 5— 1820 . . 28— 13— 13— 3— 8— 5— 38—

2.3.1 72/127 40.77 6.55 6225.8 8— 3— 11— 8815.4 8— 3— . 828.3 36— 18— 33— 3— 1— 1— 1030.5 4— . . 1— 6— . 61— 6— . 11— 8— 9638 3— . 4— 10064.5 1234.6 5723.2 2118.7 1518.2 5017.8 1116.3 1413 5811.8 12— 22— 8— 19— 14— 51—

2.4 2.3.2 18/53 39.13 11.24 22— 6— 2214.9 6— 6728.9 6— . . . 28— 6— 28— . . . . . . . . . . 5027.2 6— . 6— 6— 4432.1 . . . . . 28— . . 6— . 6— 17— 7229.5 2810.2 . . 6— 17—

2.3.3 6/42 28.33 8.28 10022.8 . . . 67— . . . . 50— . 33— . . . . . . . . . . 50— . . . . 67— . . . 83— . 17— . . . . . 83— 17— 10055.2 6741.5 5030.1 17— 50—

2.3.4 6/48 26.33 9.50 10022.8 . . . 100— . 17— . . 33— . 33— . . . . . . . . . . 33— . . . . 83— . . . 83— . 17— . . 17— . . 50— 17— 33— 17— 17— 10052.5 6721.3

2.3.5 8/46 35.75 7.52 38— 12— 1220.7 . 75— . . . . 12— . 25— 12— 2523.8 . . . . . . 12— . 50— . . 25— 12— 50— . . . 88— . 12— . . 62— . . 50— 12— 38— . 25— . 38—

2.3.6 2/31 66.67 9.39 . . . . . . . . . . . 50— . . . . . . . . . . . . . 50— . 10020.1 . . . 10022.2 . . . . 50— . . 50— . 50— . . . 50—

2.3.7 6/49 44.39 12.19 50— 17— . . 33— 17— . . . 33— 33— 33— . . . . . . . 17— . . 67— . . . . 83— . . . 50— . . 33— 17— 5031.8 . 17— 33— 17— 17— . . 17— 67—

2.4.1 3/32 40.67 7.77 33— . . . 67— . . . . 33— . 67— . 33— . . . . . . . . 67— . . 33— . 33— . . . 33— . . . . . . . . 33— . . . 33— 33—

2.4.2 3/22 49.67 13.19 33— . . . 33— . . . . 33— . 33— . . . . . . . . . . 10033.3 . . . . 33— . . . . . . . . . . . . 33— 33— . . . .

2.4.3 7/38 42.48 13.95 29— . 14— . 14— . . . . 29— 14 14— . . . . . . . . . . 10017 . . . . 29— . . . 14— . 29— . . . 14— . 14— . 14— 14— . 14— 14—

2.4.4 9/40 39.04 12.99 33— . 3326.2 . 56— . . . . 44— 22— . . . . . . . . . . . 25— . . . . 44— . . 11— 67— . 56— . . . . 11— 56— 44— 44— 4423.9 22— 22— 44—

2.4.5 2/16 31.17 11.28 10022.8 . . . 50— . . . . . . . . . . . . . . . . . 50— . . . . . . . . 50— . . . . . . . . . . . . . 50—

13

(continued on next page)

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Table 6 (continued ) 2. Typical Steppe

Vegetation-subtype

2.1

Salsola collina Potentilla acaulis Hedysarum brachypterum Festuca ovina Stellera chamaejasme Potentilla tanacetifolia Olgaea lomonosowii Lilium pumilum Hordeum roshevitzii Halerpestes ruthenica Scutellaria baicalensis Glaux maritima Agropyron mongolicum Iris lactea var. chinensis Thalictrum petaloideum Astragalus adsurgens Chenopodium aristatum Saussurea amara Silene aprica Thymus mongolicus Polygonum divaricatum Chamaerhodos erecta Scorzonera austriaca Artemisia frigida Serratula centauroides Caragana microphylla Poa pratensis Caragana stenophylla Artemisia sieversiana Leymus secalinus Ephedra sinica Allium anisopodium Tragus racemosus Lappula myosotis

35— 39— 8— . . 16— 2— . . . 2— . 4— 6— 18— 8— 4120.7 4— 6— . . 2— . 59— 45— 14— 18— 1821.1 8— . . 20— 6— 22—

56— 44— . . . . . . . . . . . . . . 33— . 11— . . . . 10029.6 11— . 22— 11— 3338.7 . . 11— . 11—

50— 25— . . . 7530.8 . . . . . . . . 25— . 50— . . . . . . 50— 75— . 50— . . 25— . . . 25—

. . . . . . . . . . . . . . 50— 50— . 50— . . . . . . 50— . 50— . . . . . . .

39— 48— 17— . . 17— 4— . . . . . . 4— . . 17— . 4— 9— . . . 52— 26— 26— 17— . . 4— . 13— . 35—

100— . . . . 50— . . . . . . . . . . . . . . . . . . 50— 50— . . . . . . . 100—

2.2

2.3

26— 3622.4 13— . . 26— . . . . . . . 5— 5— 3— 21— 8— . . . . . 26— 23— . 15— 5— 10— . . 3— . 18—

22— 40— 11— . . 49— . . . 1— 1— 1— . 7— 11— 1— 22— 21— 8— 4— . 1— . 47— 31— 8— 28— 4— 1— 4— . 8— . 31—

2.4 11— 33— 6— . . 17— . . . . . . . . . . 39— . . . . . . 5620.6 17— 6— 11— 6— 17— . . 6— . 22—

33— 17— . . . . . . . . . . . 17— 17— 17— 33— . . . . . . 33— 17— . . 5019.2 17— . . 17— . .

5020.5 17— . . . 17— . . . . . . . . 17— 17— 33— . . . . . 17— 33— 17— 17— 17— 6729.6 17— . . 17— . .

. 8850.8 3837 1234.6 1234.6 38— . . . . . . . . . . 12— . . 12— . . . 50— 12— 12— 25— . . . . . . 50—

. 50— . . . 10043.7 5069.9 5069.9 5054.4 5053.5 5044.9 5044.9 5039.4 50— 50— . . . . . . . . 50— 50— . 50— . . . . . . 50—

33— . . . . 50— . . 17— 17— . 3326.3 . 6746.8 5046.6 3330.4 6720.7 5047.6 3346.6 . . . . 33— 5031.6 . 33— . . . . 33— 17— 17—

. 33— . . . 67— . . . . 3326.3 . . 33— . . . . . 100100 3356.8 3354.7 3332.8 33— . . . . . . . . . .

33— 33— . . . 33— . . . . . . . . . . 33— . . . . . . 10057.2 10041.6 33— . . . . . . . .

14— 14— . . . . . . . . . . . . 4364.6 . 14— . . . . . 14— 57— 7121.8 10063 4364.6 14— . 14— . 14— 14— .

5619.1 . . . . . . . . . . . . . . . 22— . . . . . . 25— . 25— . 8866.8 3860.3 1127 . 11— . 11—

. . . . . . . . . . . . 5039.4 . . . 50— . . . . . . 100— . 50— . . . . 100100 10056 5046.5 5023.1

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Vegetation-type

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Table 7 Synoptic table of Desert Steppe in Hulun Buir Steppe. The meanings of contents in the table are the same as those in Table 4. Vegetation-type

3. Desert Steppe

Vegetation-subtype Formation
s/species No. of total releve Mean vegetation cover (%) Mean vegetation height (cm) Stipa tianschanica var. klemenzii Chenopodium aristatum Chenopodium album Cleistogenes squarrosa Leymus chinensis Carex korshinskyi Potentilla bifurca Allium bidentatum Allium tenuissimum Artemisia sieversiana Astragalus scaberrimus Heteropappus altaicus Euphorbia humifusa Allium polyrhizum Convolvulus ammannii Artemisia scoparia Ptilotricum tenuifolium Artemisia anethifolia Allium ramosum Caragana stenophylla Allium mongolicum Ptilotricum canescens Asparagus schoberioides

3.1 3.1.1 3/36 31.67 6.52 10078.1 6775.6 10053.7 10044.4 6763.2 10030 6733 3329.1 6729.6 3333.8 3323.2 3337.5 3322 33— 33— . . . . 67— . . .

3.2 3.2.1 8/85 32.25 8.53 7527.3 . 50— 62— 12— 7532.1 38— 12— 25— 12— . . . 10049.7 8827.2 2538.7 2532.6 1231.6 1222.3 62— . . .

3.3 3.3.1 19/30 28.39 8.25 74— . 47— 58— . 68— 21— 5— 42— . 5— 11— . 9531 8430.5 5— 11— . 5— 10041.3 2138.9 1127 1633.3

3.3.1.3. Forb meadow steppe. This vegetation subtype included 4 formations, which were mainly composed of perennial mesophyte forbs. The main edificator species were Carex pediformis, Bupleurum scorzonerifolium, Potentilla tanacetifolia and other forbs. During the research, many plots of the vegetation subtype were recorded on the eastern plains and low-mountain area of the Greater Khingan Mountains in the Hulun Buir Steppe. The community physiognomy of this vegetation-subtype is shown in Fig. 5(1.3). The plots with these edificator species occurred on grassland soil and mountain soil with the highest average cover of herb layer and average above-ground biomass, and the highest species richness, Shannon-Weiner index, Simpson index and Pielou index, among all meadow steppe vegetation subtypes (Fig. 6). 3.3.1.3.1. Form. Carex pediformis-mesophyte. Diagnostic species: Carex pediformis, Hemerocallis fulva, Lilium dauricum. Constant species: Carex pediformis, Hemerocallis fulva, Lilium dauricum, Vicia cracca, Galium verum, Sanguisorba officinalis, Geranium pratense. In the Hulun Buir Steppe, Carex pediformis steppe was divided into two formations according to community characteristics and distribution; one was a meadow steppe, which was mainly composed of mesophyte species, and the other was a typical steppe, mainly composed of xerophyte species. Here we analyzed formation Carex pediformis mainly composed of mesophyte species, which is an important type of the representative formations of meadow steppe. Due to the relatively low evaporation rate in the meadow steppe near the mountain, the soil moisture conditions during the growth season are high, which provides good growing conditions for meso-xerophilous, xero-mesophilous and mesophilous forbs. Therefore, this formation is composed of a rich variety of plant species, with colorful shapes and forms in the community and high productivity. The mean vegetation height of the Carex pediformis-mesophyte formation in forb meadow steppe was taller than the Carex pediformis-xerophytism formation in a typical steppe, which could reach 16.02 cm, and the mean height of Carex pediformis in the Carex pediformis-mesophyte formation could reach 30e40 cm. The mean cover of the herb layer was 60%. Species
. This formation had the highest species numbers per m2 plot rangedfrom 14 to 38, with a mean of 26 species per releve richness, and the total number of species in the formation was 122. The most frequent species in this community included Carex pediformis, Hemerocallis fulva, Lilium dauricum, Vicia cracca, Sanguisorba officinalis, Galium verum, Agropyron cristatum, and Geranium pratense. Other plant species in this formation were from Chenopodium, Allium, Astragalus, and Ptilotricum. 3.3.1.3.2. Form. Bupleurum scorzonerifolium. Diagnostic species: Bupleurum scorzonerifolium, Asparagus schoberioides, Haplophyllum dauricum. Constant species: Bupleurum scorzonerifolium, Asparagus schoberioides, Haplophyllum dauricum, Stipa baicalensis. Formation Bupleurum scorzonerifolium is mainly distributed in the low-lying areas in the eastern part of the Hulun Buir Steppe. Bupleurum scorzonerifolium is a kind of perennial medicinal plant of the Umbelliferae, with a mean height that can reach 30e60 cm. The mean vegetation height was 14.79 cm. The mean cover of the herb layer was 55%. Species numbers per
, and the total number of species in the formation was 63. m2 plot rangedfrom 19 to 31, with a mean of 24 species per releve

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The most frequent species in this community includedBupleurum scorzonerifolium, Leymus chinensis, Asparagus schoberioides, Haplophyllum dauricum, Artemisia scoparia, Stipa baicalensis, and Potentilla tanacetifolia. Other plant species in this formation were from theIris, Caragana, Filifolium, and Galium. 3.3.1.3.3. Form. Potentilla tanacetifolia -mesophyte. Diagnostic species: Potentilla tanacetifolia, Glaux maritima, Halerpestes ruthenica, Olgaea lomonosowii. Constant species: Potentilla tanacetifolia, Glaux maritima, Halerpestes ruthenica, Olgaea lomonosowii, Poa pratensis, Bromus inermis. Sites of this formation are embedded in the Stipa baicalensis steppe and Leymus chinensis steppe in the hilly area of eastern part of Hulun Buir Steppe. In contrast to the Potentilla tanacetifolia-xerophytism formation, this formation consists mainly of mesophytes or hygrophytes. The mean vegetation height was 8.34 cm. The mean cover of the herb layer was 64%. Species
, and the total number of species in the numbers per m2 plot ranged from 9 to 19, with a mean of 13 species per releve formation was 23. The most frequent species in this community included Potentilla tanacetifolia, Glaux maritima, Halerpestes ruthenica, Leymus chinensis, Carex duriuscula, Olgaea lomonosowii, Poa pratensis, Bromus inermis, and Saussurea amara. Other plant species in this formation were from the Chenopodium, Artemisia, Cleistogenes, and Astragalus. 3.3.1.3.4. Form. Filifolium sibiricum. Diagnostic species: Filifolium sibiricum, Sanguisorba officinalis, Geranium sibiricum, Hordeum vulgare. Constant species: Filifolium sibiricum, Sanguisorba officinalis, Geranium sibiricum, Hordeum vulgare, Poa pratensis, Leymus chinensis. The Filifolium sibiricum steppe is a specific axial root herbosa steppe association found in mountain areas in the middle of Asia, where axial root herbosa is the dominant plant community. In Hulun Buir Steppe, the Filifolium sibiricum steppe is mainly distributed in the low hill districts along the eastern and western foothills of the Greater Khingan Mountains. The mean height of Filifolium sibiricum in the forb meadow steppe could reach 20e60 cm, and the mean height of Sanguisorba officinalis could reach 30e120 cm. The mean vegetation height was 16.41 cm. The mean cover of the herb layer was 64%.
, and the total number of species in the Species numbers per m2 plot rangedfrom 16 to 18, with a mean of 17 species per releve formation was 31. The most frequent species in this community included Filifolium sibiricum, Sanguisorba officinalis, Geranium sibiricum, Hordeum vulgare, Poa pratensis, Carex pediformis, andLeymus chinensis. Other plant species in this formation were from the Artemisia, Allium, Koeleria, and Achnatherum. 3.3.1.4. Semishrub Meadow Steppe. This vegetation subtype includes only 1 formation, and the main edificator species is Caragana microphylla. Some plots of the vegetation subtype were recorded on the eastern plains and low-mountain area of the Greater Khingan Mountains in the Hulun Buir Steppe. The community physiognomy of this vegetation-subtype is shown in Fig. 5(1.4). It occurs on meadow grassland soil with the highest average height of herb layer, average dissimilarity, and the lowest species richness among all meadow steppe vegetation subtypes (Fig. 6). 3.3.1.4.1. Form. Caragana microphylla-mesophyte. Diagnostic species: Caragana microphylla, Hieracium umbellatum, Iris lactea var. chinensis, Gueldenstaedtia stenophylla, Iris tenuifolia. Constant species: Caragana microphylla, Hieracium umbellatum, Iris lactea var. chinensis, Gueldenstaedtia stenophylla, Iris tenuifolia, Achnatherum sibiricum, Medicago sativa. Formation Caragana microphylla-mesophyte is the most important of the representative formations of thicketizationmeadow steppe. In contrast to formation Caragana microphylla -xerophytism, the edificator species of native vegetation in formation Caragana microphylla-mesophyte mainly included Leymus chinensis, Poa pratensis and Stipa baicalensis. The mean vegetation height was 18.62 cm. The mean cover of the herb layer was 48%. Species numbers per m2 plot rangedfrom 16 to 31,
, and the total number of species in the formation was 44. The most frequent species in with a mean of 21 species per releve this community included Caragana microphylla, Hieracium umbellatum, Iris lactea var. chinensis, Poa pratensis, Gueldenstaedtia stenophylla, Leymus chinensis, Iris tenuifolia, Achnatherum sibiricum, and Medicago sativa. Other plant species in this formation were from the Chenopodium, Artemisia, Cleistogenes, and Astragalus.

3.3.2. Typical steppe 3.3.2.1. Bunch grass typical steppe. This vegetation subtype includes 6 formations, which are mainly composed of perennial tufted xerophytic grasses; the main edificator species are Stipa grandis, Stipa sareptana var. krylovii, Cleistogenes squarrosa, Koeleria cristata, Agropyron cristatum, and Agropyron desertorum. During the research, many plots of the vegetation subtype were recorded on the central and eastern plains and hilly area in the Hulun Buir Steppe. The community physiognomy of this vegetation-subtype is shown in Fig. 5(2.1). The plots with these edificator species occurred on grassland soil and sandy soil with the lowest average cover of herb layer and the highest average dissimilarity among all typical steppe vegetation subtypes (Fig. 6). 3.3.2.1.1. Form. Stipa grandis. Diagnostic species: Stipa grandis, Medicago ruthenica, Cleistogenes squarrosa. Constant species: Stipa grandis, Medicago ruthenica, Cleistogenes squarrosa, Leymus chinensis, Chenopodium aristatum, Caragana stenophylla. Floristic and habitat characteristics

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Stipa grandis steppe is centrally distributed in the steppe belt of the Mongolian Plateau and it is the primary steppe type within the typical steppe. Formation Stipa grandis is a representative typical steppe landscape, and it is distributed in the high plain of the central and eastern Hulun Buir Steppe. Formation Stipa grandis, one of the representative formations of the typical steppe, associated with the Stipa baicalensis community, Filifolium sibiricum community, and Leymus chinensis community, is a specific bunch grass steppe. The soil is a thick layer of typical loam and sandy loam chestnut soil and dark chestnut soil, much of which has eroded over the last few decades. When the habitat conditions become drier, the Stipa grandis steppe will be replaced by the xeromorphic Stipa sareptana var. krylovii steppe. Therefore, Stipa grandis steppe can be regarded as the typical representative steppe of mesothermal steppes of China. According to the classification of natural zones, Stipa grandis steppe is an important indicator for the classification of the mesothermal forest-grassland subbelt, typical steppe subbelt and desert steppe subbelt. As an original community group, Stipa grandis steppe forms an association with various herbosa. Stipa grandis is the tallest dense-cluster grass in Stipa plants in China, with a mean leaf height reaching 40e50 cm and fertile tillers reaching 80e100 cm. The mean vegetation height was 21.69 cm. The total cover of the herb layer was considerably higher, between 35 and 62% (mean 56%). The phytocoenosis was characterized by a moderate species richness. Species
, and the total number of species in the numbers per m2 plot ranged from 9 to 26, with a mean of 15 species per releve formation was 82. The seasonal aspect of formation Stipa grandis was not as colorful as formation Stipa baicalensis, but simple and unadorned. The floristic complexity of formation Stipa grandis were less than Stipa baicalensis. It is regional, and its origin has some connections with Eurasian grassland and North American grassland. The most frequent species in this community included Cleistogenes squarrosa, Leymus chinensis, Agropyron cristatum, Carex duriuscula and Artemisia frigida. Other plant species of the Stipa grandis steppe were from the Chenopodium, Potentilla, Artemisia and Allium, indicative of typical steppes in the semiarid zone. 3.3.2.1.2. Form. Stipasareptana var. krylovii. Diagnostic species: Stipa sareptana var. krylovii, Lepidium apetalum. Constant species: Stipa grandis, Lepidium apetalum, Cleistogenes squarrosa, Agropyron cristatum. The Stipa sareptana var. krylovii steppe is associated with herbosa steppes similar to the Stipa grandis steppe, both of which are common associations in Asian steppes. Stipa sareptana var. krylovii steppe is mainly distributed in typical steppe areas of the Mongolian Plateau, stretching northward and eastward to the boundary of the forest-grassland belts. In the south, it is located in the semiarid zone of the Loess Plateau in China and to the west, it is distributed in mountain areas in the arid zone, such as the Yinshan, Helan, Qilian and Tianshan Mountains. In the Inner Mongolian Plateau areas, a large area of this type of steppe is distributed in a typical steppe belt alternating with the Stipa grandis steppe. This alternating steppe belt is mainly distributed in the central and western parts of the Hulun Buir Plateau and the Xilin Gol Plateau. The climate is a mesothermic semiarid climate, and the topography is open with flat uplands and hilly slopes. The soil is mainly comprised with loamy soil, sandy loam or sandy chestnut soil. Formation Stipa sareptana var. krylovii and formation Stipa grandis are representative formations of typical steppes. In typical steppe regions, both are similarly distributed. Formation Stipa grandis has been gradually substituted with formation Stipa sareptana var. krylovii nearing the side of the desert steppe, since the later has higher drought tolerance than the former. Stipa sareptana var. krylovii is a xerophyte in the typical steppe, and its associations are similar to those of Stipa grandis, but the community is more restricted. However, in the western part of the typical steppe belt (adjacent to areas of desert steppe), the quantity and function of Stipa sareptana var. krylovii exceeds that of Stipa grandis and has becomes the dominant plant association. Formation Stipa sareptana var. krylovii is the most fundamental pasture in North China, and overgrazing and reclamation may easily include land desertification. Stipa sareptana var. krylovii is a tall dense-cluster grass in Stipa plants, with mean height reaching 30e60 cm. The mean vegetation height was 18.69 cm. The total cover of the herb layer was considerably higher, between 20 and 61% (mean 34%). The phytocoenosis was characterized by moderate species richness. Species numbers per m2 plot ranged from 8 to 23, with a
, and the total number of species in the formation was 43. The species composition of formation mean of 13 species per releve Stipa sareptana var. krylovii was simple, reflecting the characteristics of a typical steppe. The most frequent species in this community included Agropyron cristatum, Artemisia frigida, Allium tenuissimum, and Cleistogenes squarrosa. Other plant species of theStipa sareptana var. krylovii steppe were from the Chenopodium, Salsola, and Artemisia. These plants are indicative of a typical steppe in the semiarid zone. 3.3.2.1.3. Form. Cleistogenes squarrosa. Diagnostic species: Cleistogenes squarrosa, Gueldenstaedtia stenophylla. Constant species: Cleistogenes squarrosa, Gueldenstaedtia stenophylla, Medicago sativa, Allium tenuissimum, Setaria viridis. Formation Cleistogenes squarrosa belongs to shortgrass steppes. This type formation is mainly distributed in the sandy grassland of central Hulun Buir Steppe. The soils mainly comprise sandy chestnut soil, loamy soil or sandy loam. During the growing period, Cleistogenes squarrosa was fed by various livestock, and most of the other plant elements in the community were also good forage grass. Therefore, formation Cleistogenes squarrosa is a better natural pasture, especially suitable for grazing sheep. However, this type of steppe is in the stage of grazing degradation, with relatively low productivity and low and sparse plants. Therefore, protection and management should be strengthened for its gradual restoration. Cleistogenes squarrosa is a xerophytic bunch shortgrass, the mean height of which was only 10e30 cm. The mean vegetation height was 12.08 cm. The total cover of the herb layer was considerably higher, between 30 and 51% (mean 33%). The phytocoenosis was characterized by moderate species richness. Species numbers per m2 plot ranged from 15 to 19, with a
, and the total number of species in the formation was 40. The species composition of formation mean of 18 species per releve Cleistogenes squarrosa was simple, reflecting the characteristics of a typical steppe. The most frequent species in this

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community included Allium tenuissimum, Artemisia scoparia, Potentilla tanacetifolia, Serratula centauroides and Setaria viridis. Other plant species of the Cleistogenes squarrosa steppe were from the Pulsatilla, Hieracium, and Koeleria. 3.3.2.1.4. Form. Koeleria cristata. Diagnostic species: Koeleria cristata, Euphorbia fischeriana. Constant species: Koeleria cristata, Euphorbia fischeriana, Polygonum lapathifolium, Artemisia annua. In the Hulun Buir Plateau, formation Koeleria cristata is widely distributed in the sandy land on the south bank of Hailar River and in the sandy land of Xin Barag Zuoqi. The soils mainly comprise sandy loam or sandy chestnut soil. It is very unstable, and the edificatory species often change according to changesin the substrate soil. On a high level of sand soil fixation, the number of Agropyron cristatum often increases, and it is too difficult to transition formation Agropyron cristatum or even develop formation Stipa grandis. Thus, formation Koeleria cristata falls into a stage of sand-vegetation succession. The productivity of this type of steppe community is medium, and the high-quality herbage accounts for 70e80%. It is a kind of pasture. However, because of sandy substrates, overgrazing can cause quicksand, so care must be taken to protect and plan grazing. Koeleria cristata is a perennial dense-cluster grass, the mean height of which could reach 25e60 cm. The mean vegetation height was 18 cm. The total cover of the herb layer was considerably higher, between 29 and 41% (mean 32%). The phytocoenosis was characterized by moderate species richness. Species numbers per m2 plot ranged from 12 to 23, with a mean of
, and the total number of species in the formation was 31. The species composition of formation Koeleria 17 species per releve cristata was simple. The most frequent species in this community included Euphorbia fischeriana, Stipa baicalensis, and Polygonum lapathifolium. Other plant species of the Koeleria cristata steppe were from Astragalus, Agropyron, and Thalictrum. 3.3.2.1.5. Form. Agropyron cristatum. Diagnostic species: Agropyron cristatum, Lespedeza davurica. Constant species: Agropyron cristatum, Lespedeza davurica, Stipa grandis, Filifolium sibiricum. Formation Agropyron cristatum is a kind of grassland that is unique to the overlying sandy area in grassland regions. In the Hulun Buir Plateau, it is widely distributed in the sandy land on the south bank of the Hailar River, the sandy land of Xin Barag Zuoqi or porphyritic distribution on sandy soil areas of typical steppe region. The soils mainly comprise sandy loam or sandy chestnut soil. Like formation Koeleria cristata, formation Agropyron cristatum is very unstable. Generally, it appears as a companion species of Stipa steppe and Leymus chinensis steppe, but on the overlying sandy land or sandy soil, it can appear as an edificator species and form formation Agropyron cristatum. Agropyron cristatum grows mixing with Koeleria cristata, and Cleistogenes squarrosa, forming a short-grass steppe, which can be regarded as an unstable transition type in the stage of sandvegetation succession. The area of formation Agropyron cristatum is very small and often unsteady. Therefore, grazing pressure must be controlled to avoid grassland desertification. Agropyron cristatum is a xerophytic bunch grass, with a mean height that could reach 22e60 cm. The mean vegetation height was 11 cm. The total cover of the herb layer was considerably higher, between 20 and 48% (mean 30%). Phytocoenosis was characterized by moderate species richness. Species numbers per m2 plot rangedfrom 6 to 20, with a mean of 12 species
, and the total number of species in the formation was 64. The species composition of formation Agropyron cristatum per releve was simple. The most frequent species in this community included Cleistogenes squarrosa, Lespedeza davurica, Stipa grandis, and Carex duriuscula. Other plant species of Koeleria cristata steppe were from the Chenopodium, Allium, Potentilla, and Artemisia. 3.3.2.1.6. Form. Agropyron desertorum. Diagnostic species: Agropyron desertorum, Koeleria cristata. Constant species: Agropyron desertorum, Koeleria cristata, Artemisia lavandulaefolia, Chenopodium album. Formation Agropyron desertorum is a kind of grassland that is unique to the overlying sandy area of the grassland region. In the Hulun Buir Plateau, it is widely distributed in the sandy land, hilly land, hillside and dune lowland on the south bank of Hailar River, Xin Barag Zuoqi and Ewenkiqi, or sandy soil areas of typical steppe and desert steppe regions. The soils mainly comprise sandy loam or sandy chestnut soil. In contrast to formation Agropyron cristatum, the drought tolerance and sandliving ability of formation Agropyron desertorum is stronger. Generally, it appears as a companion species of Cleistogenes squarrosa steppe and Stipa tianschanica var. klemenzii steppe, but on the overlying sandy land or sandy soil, it can appear as an edificator species and form formation Agropyron desertorum. Thus, it can be regarded as an unstable transition type in the sand-vegetation succession stage. Agropyron desertorum is a super-xerophytic bunch grass, with a mean height reaching 20e70 cm. The mean vegetation height was 18 cm. The total cover of the herb layer was considerably higher, between 29 and 41% (mean 35%). Phytocoenosis was characterized by moderate species richness. Species numbers per m2 plot ranged from 10 to 14, with a mean of 12 species
, and the total number of species in the formation was 17. The species composition of formation Agropyron per releve desertorum was simple. The most frequent species in this community included Artemisia lavandulaefolia, Koeleria cristata, Chenopodium album, Salsola collina, and Artemisia scoparia. Other plant species of the Agropyron desertorum steppe were from Serratula, Lappula, and Caragana. 3.3.2.2. Rhizome grass typical steppe. This vegetation subtype included only 1 formation, and the main edificator species is Leymus chinensis. It occurs in the central and eastern plains in the Hulun Buir Steppe with the highest average herb layer cover and the lowest Shannon-Weiner and Simpson indices among all typical steppe vegetation subtypes (Fig. 6). The community physiognomy of this vegetation-subtype is shown in Fig. 5(2.2). 3.3.2.2.1. Form. Leymus chinensis-xerophytism. Diagnostic species: Leymus chinensis, Stipa grandis, Carex duriuscula.

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Constant species: Leymus chinensis, Stipa grandis, Carex duriuscula, Potentilla acaulis, Polygonum sibiricum, Youngia tenuicaulis. Here we analysis formation Leymus chinensis mainly composed of xerophyte species, which is similar to the community characteristics of Stipa steppe in a typical steppe region. The soils mainly comprise light loamy dark chestnut soil and chernozem. Formation Leymus chinensis-xerophytism is one of the most representative formations of a typical steppe. Among the typical steppes, the area of this formation is slightly smaller than Stipa steppe, but it still contains various steppe types. It is the steppe type with the highest economic value for grazing purposes. Its dominant synusia is mainly composed of xerophytic steppe grass, including Stipa grandis, Stipa sareptana var. krylovii, Agropyron cristatum, and Koeleria cristata. In typical steppe regions, all of these are distributed evenly. Formation Leymus chinensis of typical steppes occupies a typical zonal grassland habitat. It is widely distributed in high plains and hilly slopes with good drainage, generally in the middle and lower part of hilly slopes. It is not affected by groundwater, surface runoff is not excessive, and the vegetation thrives on the natural precipitation. The mean height of Leymus chinensis in typical steppe is shorter than in meadow steppe, reaching only 5e22 cm. The mean vegetation height was 10.22 cm, but the total cover of the herb layer was considerably higher, between 38 and 64% (mean 46%). The phytocoenosis was characterized by moderate species richness. Species numbers per m2 plot ranged from 8 to 23,
, and the total number of species in the formation was 77. The species composition of with a mean of 10 species per releve formation Leymus chinensis in a typical steppe was simple, reflecting the characteristics of a typical steppe. The most frequent species in this community included Carex duriuscula, Cleistogenes squarrosa, Potentilla acaulis, and Artemisia scoparia. Other plant species in this formation were from the Chenopodium, Agropyron, Koeleria, and Taraxacum. 3.3.2.3. Forbs Typical Steppe. This vegetation subtype includes 7 formations, mainly composed of perennial xerophytic and mesoxerophytes forbs, and the main edificator species are Carex duriuscula, Carex pediformis, Allium bidentatum, Allium ramosum, Potentilla acaulis, Potentilla tanacetifolia and other forbs. During the research, many plots of the vegetation subtype were recorded on the central and eastern plains and hilly area in the Hulun Buir Steppe. The community physiognomy of this vegetation-subtype is shown in Fig. 5(2.3). The plots with these edificator species occurred on grassland soil and mountain soil with the lowest average herb layer height, above-ground biomass and average dissimilarity, lowest richness, and highest Pielou index, among all typical steppe vegetation subtypes (Fig. 6). 3.3.2.3.1. Form. Carex duriuscula. Diagnostic species: Carex duriuscula, Cleistogenes squarrosa, Stipa grandis, Leymus chinensis. Constant species:Carex duriuscula, Cleistogenes squarrosa, Stipa grandis, Leymus chinensis, Chenopodium album, Potentilla bifurca, Taraxacum mongolicum. Formation Carex duriuscula is a type with strong drought resistance and salt tolerance, can distributed in saline meadow and saline steppe, and it is also widely distributed in Stipa steppe, Leymus chinensis steppe and short-grass steppe. It can even be found in desert steppes to the west of the Hulun Buir Steppe, but it is most widely distributed in typical steppe. The soil consists of a thin layer of typical loam and sandy loam chestnut soil, dark chestnut soil or sandy chestnut soil. As an auxiliary element, Carex duriuscula is symbiotic with the Stipa steppe and Leymus chinensis steppe. In the case of overgrazing, livestock trampling strongly on the steppe, or no rainfall for a long period, Carex duriuscula will replace Stipa species or Leymus chinensis as an edificator species and form formation Carex duriuscula. Formation Carex duriuscula, mainly composed of Carex duriuscula, is the community succession variant of formation Stipa grandis, formation Stipa sareptana var. krylovii and formation Leymus chinensis. Thus, it can be regarded as an unstable transition type in the stage of the Stipa steppe or Leymus chinensis steppe vegetation succession. Formation Carex duriuscula is also the main pasture in the Hulun Buir Steppe, providing the basic forage sources for the local livestock and wild animals; although its stem is hard, palatability and production are poor. Carex duriuscula is a eurytopic xerophytic short Carex grass, with a mean height of only 5e15 cm. The mean vegetation height was 6.5 cm. The total cover of the herb layer was considerably higher, between 26 and 63% (mean 40%). Phytocoenosis was characterized by moderate species richness. Species numbers per m2 plot ranged from 6 to 32, with a mean of 11 species
, and the total number of species in the formation was 127. The species composition of formation Agropyron per releve desertorum was simple. The most frequent species in this community included Cleistogenes squarrosa, Stipa grandis, Leymus chinensis, Chenopodium album, Potentilla bifurca, Taraxacum mongolicum, and Potentilla tanacetifolia. Other plant species of the Agropyron desertorum steppe were from the Artemisia, Allium, Hedysarum and Saussurea. 3.3.2.3.2. Form. Carex pediformis-xerophytism. Diagnostic species: Carex pediformis, Artemisia frigida, Cleistogenes squarrosa. Constant species: Carex pediformis, Artemisia frigida, Cleistogenes squarrosa, Agropyron cristatum, Stipa sareptana var. krylovii, Leymus chinensis. Formation Carex pediformis-xerophytism is mainly distributed at the bottom of the arid hills in the eastern part of the typical steppe in Hulun Buir. The mean height of Carex pediformis in typical steppe was shorter than in meadow steppes, which could only reach 10e22 cm. The mean vegetation height was 11.24 cm. The mean herb layer cover was 39%. Species
, and the total number of species in the fornumbers per m2 plot ranged from 4 to 21, with a mean of 11 species per releve mation was 53. The species composition of formation Carex pediformis in a typical steppe was simple, reflecting the characteristics of a typical steppe. The most frequent species in this community included Carex pediformis, Artemisia frigida, Cleistogenes squarrosa, Agropyron cristatum, Stipa sareptana var. krylovii, Leymus chinensis, Chenopodium aristatum, Allium

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bidentatum, and Agropyron cristatum. Other plant species in this formation were from the Potentilla, Chenopodium, Artemisia, and Lappula. 3.3.2.3.3. Form. Allium bidentatum. Diagnostic species: Allium bidentatum, Convolvulus ammannii. Constant species: Allium bidentatum, Convolvulus ammannii, Stipa grandis, Allium senescens, Caragana stenophylla. Allium bidentatum is a drought-tolerant plant in the Allium genus, and it is widely distributed in the central part of the typical steppe in Hulun Buir. Formation Allium bidentatum is one of the most representative formations in sandy soil of the Allium steppe. The mean height of Allium bidentatum in Allium steppe was shorter, reaching only 10e20 cm. The mean vegetation height was 8.28 cm. The mean herb layer cover was 28%. Species numbers per m2 plot ranged from 9 to 28, with a
, and the total number of species in the formation was 42. The most frequent species in this mean of 14 species per releve community included Allium bidentatum, Convolvulus ammannii, Stipa grandis, Allium senescens, Cleistogenes squarrosa, Carex duriuscula, Caragana stenophylla, and Potentilla bifurca. Other plant species in this formation were from the Koeleria, Chenopodium, and Iris. 3.3.2.3.4. Form. Allium ramosum. Diagnostic species: Allium ramosum, Artemisia scoparia. Constant species: Allium ramosum, Artemisia scoparia, Stipa grandis, Salsola collina, Caragana stenophylla. Allium ramosum is widely distributed in the Hulun Buir Plateau, especially in sandy or hilly typical steppe regions. Formation Allium ramosum is one of the most representative formations in Allium steppe, and it is a valuable forage resource in the typical Allium steppe with high nutritional value. When sheep and camels are grazedin Allium ramosum steppe in autumn, the quality of the meat and milk improves. The mean height of Allium ramosum in a typical steppe could reach 20e65 cm. The mean vegetation height was 9.50 cm. The mean herb layer cover was 26%. Species numbers per m2 plot ranged from 9 to 36,
, and the total number of species in the formation was 48. The most frequent species in with a mean of 14 species per releve this formation included Allium ramosum, Cleistogenes squarrosa, Carex duriuscula, Artemisia scoparia, Stipa grandis, Salsola collina, and Caragana stenophylla. Other plant species in this formation were from the Chenopodium, Serratula, Poa, and Taraxacum. 3.3.2.3.5. Form. Potentilla acaulis. Diagnostic species: Potentilla acaulis, Hedysarum brachypterum. Constant species: Potentilla acaulis, Hedysarum brachypterum, Festuca ovina, Stellera chamaejasme, Stipa baicalensis. Potentilla acaulis is a xerophyte in warm temperate grassland, which is widely distributed in the central and western regions of the Hulun Buir Steppe regions and does not tolerate the influence of groundwater plateau hilly or slope as an auxiliary species. When the grassland severely degenerates, it will replace the original edificator species to occupy the dominant ecological niche. Thus, it is also an indicator species of grassland degradation. The soil adaptability of this formation is very wide, and it can grow well in light chestnut soil, dark chestnut soil, dark chestnut soil or dark loessial soils. The mean height of Potentilla acaulis in typical steppes was much shorter, reaching only 2e15 cm. The mean vegetation height was 7.52 cm. The mean herb layer cover was 36%. Species numbers per m2 plot ranged from 9 to 20, with a mean of 14 species per
, and the total number of species in the formation was 46. The most frequent species in this community included releve Potentilla acaulis, Hedysarum brachypterum, Taraxacum mongolicum, Festuca ovina, Stellera chamaejasme, Carex duriuscula, and Stipa baicalensis. Other plant species in this formation were from the Agropyron, Chenopodium, and Thymus. 3.3.2.3.6. Form. Potentilla tanacetifolia-xerophytism. Diagnostic species: Potentilla tanacetifolia, Olgaea lomonosowii, Lilium pumilum, Hordeum roshevitzii, Halerpestes ruthenica, Scutellaria baicalensis, Glaux maritima. Constant species: Potentilla tanacetifolia, Olgaea lomonosowii, Lilium pumilum, Hordeum roshevitzii, Halerpestes ruthenica, Scutellaria baicalensis, Glaux maritima, Agropyron mongolicum, Leymus chinensis, Carex duriuscula. Formation Potentilla tanacetifolia-xerophytism is one of the most representative formations of Potentilla typical steppe. The mean height of Potentilla tanacetifolia was taller a forb typical steppe, reaching 20e50 cm. The mean vegetation height was 9.39 cm. The mean herb layer cover was 67%. Species numbers per m2 plot ranged from 11 to 23, with a mean of 17 species per
, and the total number of species in the formation was 31. The most frequent species in this community included releve Potentilla tanacetifolia, Leymus chinensis, Carex duriuscula, Iris lactea var. chinensis, Thalictrum petaloideum, Hordeum roshevitzii, and Artemisia frigida. Other plant species in this formation were from the Lappula, Filifolium, and Taraxacum. 3.3.2.3.7. Form. Other forbs. Diagnostic species: Iris lactea var. chinensis, Thalictrum petaloideum. Constant species: Iris lactea var. chinensis, Thalictrum petaloideum, Chenopodium aristatum, Saussurea amara, Taraxacum mongolicum. The edificator species of other forb formations included Iris lactea var. chinensis and Thalictrum petaloideum, which is a azonal vegetation type in typical steppes and mosaic-distributed in the Stipa steppe and Allium steppe. The mean height of Iris lactea var. chinensis in forb typical steppes was taller, reaching 30e70 cm, and the mean height of Thalictrum petaloideum could reach 30e80 cm. The mean vegetation height was 12.19 cm. The mean herb layer cover was 44%. Species numbers per
, and the total number of species in the formation was 49. The m2 plot ranged from 9 to 30, with a mean of 15 species per releve most frequent species in this community included Iris lactea var. chinensis, Thalictrum petaloideum, Chenopodium aristatum, Serratula centauroides, Saussurea amara, Taraxacum mongolicum, and Artemisia scoparia. Other plant species in this formation were from the Tragus, Lappula, and Hordeum. 3.3.2.4. Semishrub Typical Steppe. This vegetation subtype includes 5 formations, which are mainly composed of perennial xerophytic semishrubs, and the main edificator species are Thymus mongolicus, Artemisia frigida, Caragana microphylla, Caragana stenophylla and Ephedra sinica. During the research, many plots of this vegetation subtype were recorded on the

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central and eastern plains and hilly and low mountain areas in the Hulun Buir Steppe. The community physiognomy of this vegetation-subtype is shown in Fig. 5(2.4). The plots with these edificator species occurred on grassland soil, desert grassland soil and mountain soil, with the highest average herb layer height and above-ground biomass and the highest species richness, Shannon-Weiner index and Simpson index among all typical steppe vegetation subtypes (Fig. 6). 3.3.2.4.1. Form. Thymus mongolicus. Diagnostic species: Thymus mongolicus, Polygonum divaricatum, Chamaerhodos erecta. Constant species: Thymus mongolicus, Polygonum divaricatum, Chamaerhodos erecta, Scorzonera austriaca, Scutellaria baicalensis. Formation Thymus mongolicus is a peculiar steppe type composed of Thymus mongolicus and other xerophyte species. And it occupies a certain area on the fixed sandy land of Hulun Buir. Formation Thymus mongolicus is mainly distributed in typical steppe regions, and it also extends to meadow steppe regions but generally does not enter the desert steppe region. From originating sources, formation Thymus mongolicus can be divided into two types: one is original, often growing in extreme habitat, such as skeleton soil and cretaceous outcrops, and the other is the retrogressive succession stage of the original grass steppe due to extensive grazing and erosion. In nature, the later phenomenon is more universal. Thymus mongolicus is a dwarf subshrub with volatile bioactive compounds and a sweet smell. It not only is of high-quality, but the raw material is also useful for producing essence and condiment, and it is called “ground Chinese prickly ash” by herdsmen. The mean height could only reach 2e10 cm. The mean vegetation height was 7.77 cm. The mean cover of the herb
, and the total number of layer was 41%. Species numbers per m2 plot rangedfrom 13 to 23, with a mean of 16 species per releve species in the formation was 32. The most frequent species in this community included Thymus mongolicus, Cleistogenes squarrosa, Polygonum divaricatum, Koeleria cristata, Chamaerhodos erecta, Scorzonera austriaca, and Scutellaria baicalensis. Other plant species in this formation were from the Tragus, Lappula, and Hordeum. 3.3.2.4.2. Form. Artemisia frigida. Diagnostic species: Artemisia frigida, Serratula centauroides, Chamaerhodos erecta. Constant species: Artemisia frigida, Serratula centauroides, Chamaerhodos erecta, Agropyron cristatum. The main species of formation Artemisia frigida is the small subshrub Artemisia frigida, and its succession pattern has changed under the impacts of overgrazing and strong wind erosion in steppe areas. Artemisia frigida steppe is mainly distributed in the central and western hilly top of Hulun Buir Steppe. It is classified as a semiarid typical steppe, and its typical zonal plants are the Stipa grandis steppe and Stipa sareptana var. krylovii steppe. Due to long-term overgrazing and trampling, herbosa growth has been limited, and the drought-tolerant Artemisia frigida has been replaced by the original dominant plants and the steppe developed into an Artemisia frigida steppe. The growth of Artemisia frigida steppe is closely related to the long-term wind erosion and substratum conditions. Artemisia frigida is a dwarf semibush characterized by its extensive root system, high sprouting and root growth potential, tolerance to trampling and adaptability to soil erosion. The mean height could reach 30e60 cm. The mean vegetation height was 13.19 cm. The mean herb layer cover was 50%. Species numbers per m2 plot ranged from 13 to 22, with a mean of 16
, and the total number of species in the formation was 22. The most frequent species in this community species per releve included Artemisia frigida, Serratula centauroides, Chamaerhodos erecta, and Agropyron cristatum. Other plant species in this formation were from the Stipa, Cleistogenes, Setaria, and Leymus. 3.3.2.4.3. Form. Caragana microphylla. Diagnostic species: Caragana microphylla, Caragana microphylla, Poa pratensis. Constant species: Caragana microphylla, Caragana microphylla, Poa pratensis, Serratula centauroides. Formation Caragana microphylla is one of the most representative formations of a thicketization-typical steppe. The edificator species of native vegetation included Stipa grandis, Stipa sareptana var. krylovii, Cleistogenes squarrosa and Leymus chinensis. The mean height of Caragana microphylla in typical steppe was taller, reaching 100e200 cm. The mean vegetation height was 13.95 cm. The mean cover of the herb layer was 42%. Species numbers per m2 plot ranged from 13 to 22, with a
, and the total number of species in the formation was 38. The most frequent species in this mean of 17 species per releve community included Caragana microphylla, Agropyron cristatum, Caragana microphylla, Poa pratensis, Artemisia frigida, Serratula centauroides, and Leymus chinensis. Other plant species in this formation were from the Setaria, Carex, and Chenopodium. 3.3.2.4.4. Form. Caragana stenophylla-typical. Diagnostic species: Caragana stenophylla, Artemisia sieversiana. Constant species: Caragana stenophylla, Artemisia sieversiana, Leymus secalinus, Salsola collina, Convolvulus ammannii, Stipa sareptana var. krylovii. Formation Caragana stenophylla-typical is another representative formation of the thicketization-typical steppe. The edificator species of the native vegetation included Stipa sareptana var. krylovii, Stipa grandis, Koeleria cristata, Carex duriuscula and Leymus secalinus. The mean height of Caragana stenophylla in a typical steppe was shorter than Caragana microphylla, reaching 30e80 cm. The mean vegetation height was 12.99 cm. The mean cover of the herb layer was 39%. Species numbers
, and the total number of species in the formation was 40. per m2 plot ranged from 4 to 16, with a mean of 11 species per releve The most frequent species in this community included Caragana stenophylla, Artemisia sieversiana, Potentilla bifurca, Leymus secalinus, Salsola collina, Carex duriuscula, Convolvulus ammannii, and Stipa sareptana var. krylovii. Other plant species in this formation were from the Potentilla, Carex, Youngia, and Setaria. 3.3.2.4.5. Form. Ephedra sinica. Diagnostic species: Ephedra sinica, Allium anisopodium, Tragus racemosus. Constant species: Ephedra sinica, Allium anisopodium, Tragus racemosus, Lappula myosotis, Agropyron mongolicum, Stipa grandis.

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Formation Ephedra sinica distributed in plains, hillsides, riverbeds, and grasslands, and it can form a community as a edificator species in typical steppes of Hulun Buir Steppe. Ephedra sinica is an important medicinal plant, which is rich in alkaloid hemp. The mean height of it in typical steppe was shorter than Caragana microphylla, reaching 20e40 cm. The mean vegetation height was 11.28 cm. The mean cover of the herb layer was 31%. Species numbers per m2 plot ranged from 9 to 12,
, and the total number of species in the formation was 16. The most frequent species in with a mean of 10 species per releve this community included Ephedra sinica, Artemisia frigida, Allium anisopodium, Tragus racemosus, Lappula myosotis, Agropyron mongolicum, Stipa grandis, and Chenopodium aristatum. Other plant species in this formation were from the Agropyron, Carex, Cleistogenes, and Artemisia.

3.3.3. Desert steppe 3.3.3.1. Bunch grass desert steppe. This vegetation subtype includes only 1 formation, mainly composed of perennial xerophytic bunch grass, and the main edificator species is Stipa tianschanica var. klemenzii. Some plots of the vegetation subtype were recorded on the western plains in the Hulun Buir Steppe. It occurs on desert grassland soil, the substrate is partly deprived of an organic soil layer and the ground is covered by small amounts of stable rocky debris. The community physiognomy of this vegetation-subtype is shown in Fig. 5(3.1). It distributed with the lowest average herb layer cover, average herb layer height, and above-ground biomass and the highest species richness, Shannon-Weiner index and Simpson index among all desert steppe vegetation subtypes (Fig. 6). 3.3.3.1.1. Form. Stipa tianschanica var. klemenzii. Diagnostic species: Stipa tianschanica var. klemenzii, Chenopodium aristatum, Chenopodium album, Cleistogenes squarrosa, Leymus chinensis. Constant species: Stipa tianschanica var. klemenzii, Chenopodium aristatum, Chenopodium album, Cleistogenes squarrosa, Leymus chinensis, Carex korshinskyi, Potentilla bifurca, Allium tenuissimum. Stipa tianschanica var. klemenzii steppe is a small type of herbosa-associated steppe in the desert steppe region of Mongolia Plateau. It is the most drought-tolerant of the Stipa steppe, and its distribution is closely related to the location of the continental arid climate in the temperate zone. So this formation is mainly distributed in the arid western part of Hulun Buir Steppe as an azonal formation. In the spring and autumn seasons (particularly in spring), drought occurs for 4e6 months and seriously affects the stability of the steppe productivity. Stipa tianschanica var. klemenzii is a typical component of the desert plant community in the Gobi-Mongolia area in Central Asia. The mean height of it in Hulun Buir desert steppe was shorter than other Stipa species, reaching only 17e23 cm. The mean vegetation height was 6.52 cm. The mean cover of the herb layer was 32%. Species numbers per m2 plot ranged from 9 to 13,
, and the total number of species in the formation was 36. The most frequent species in with a mean of 11 species per releve this community included Stipa tianschanica var. klemenzii, Chenopodium aristatum, Chenopodium album, Cleistogenes squarrosa, Leymus chinensis, Carex korshinskyi, Potentilla bifurca, and Allium tenuissimum. Other plant species in this formation were from the Convolvulus, Agropyron, Caragana, and Euphorbia. 3.3.3.2. Forb Desert Steppe. This vegetation subtype includes only 1 formation, which is mainly composed of the perennial xerophytic forb, and the main edificator species is Allium polyrhizum. Some plots of the vegetation subtype were recorded on the western plains in the Hulun Buir Steppe. It occurs on desert grassland soil and sandy soil, and the ground is covered by some fine gravel. The community physiognomy of this vegetation-subtype is shown in Fig. 5(3.2). It is distributed with the lowest average dissimilarity and the lowest Shannon-Weiner index, Simpson index and Pielou index among all desert steppe vegetation subtypes (Fig. 6). 3.3.3.2.1. Form. Allium polyrhizum. Diagnostic species: Allium polyrhizum. Constant species: Allium polyrhizum, Convolvulus ammannii, Artemisia scoparia, Ptilotricum tenuifolium, Artemisia anethifolia, Allium ramosum, Carex korshinskyi. Formation Allium polyrhizum is extensively distributed in the Mongolian Plateau, appearing in the arid western part of Hulun Buir Steppe as an azonal formation. Formation Allium polyrhizum occupies a large area of salinized brown calcic soil and becomes the concentrated distribution area of Allium desert steppe. The seasonal aspect of formation Allium polyrhizum often fluctuates with the interannual precipitation and during the rainy season. Commonly, Allium polyrhizum germinates in early spring, when it snows more in winter or experiences some rainfall in spring. Allium polyrhizum is a valuable forage resource in the desert steppe, and it has high nutritional value. When sheep and camels are grazed in Allium polyrhizum steppe in autumn, the quality of the meat and milk improves, estrus of the livestock can be promoted, and the reproduction rate of the animals improves. Allium polyrhizum is a kind of typical superxeric bunch bulbaceous plant with strong grazing tolerance ability. Its mean height was shorter in desert steppe than other Allium species of typical steppes, reaching only 7e35 cm. The mean vegetation height was 8.53 cm. The mean cover of the herb layer was 32%. Species numbers per m2 plot ranged from 6 to 13, with a mean
, and the total number of species in the formation was 85. The most frequent species in this community of 9 species per releve included Allium polyrhizum, Convolvulus ammannii, Caragana stenophylla, Artemisia scoparia, Ptilotricum tenuifolium, Agropyron cristatum, Artemisia anethifolia, Allium ramosum, and Carex korshinskyi. Other plant species in this formation were from the Artemisia, Filifolium, Caragana, and Euphorbia.

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3.3.3.3. Semishrub desert steppe. This vegetation subtype includes only 1 formation, which is mainly composed of perennial xerophytic semishrubs, and the main edificator species is Caragana stenophylla. Some plots of the vegetation subtype were recorded on the western plains in the Hulun Buir Steppe, occurring on desert grassland soil and sandy soil. The community physiognomy of this vegetation-subtype is shown in Fig. 5(3.3). It distributed with the highest average above-ground biomass among all desert steppe vegetation subtypes (Fig. 6). 3.3.3.3.1. Form. Caragana stenophylla-desert. Diagnostic species: Caragana stenophylla, Artemisia sieversiana. Constant species: Caragana stenophylla, Artemisia sieversiana, Leymus secalinus, Salsola collina, Convolvulus ammannii, Stipa sareptana var. krylovii. Formation Caragana stenophylla-desert is the most important of the representative formations of thicketization-desert steppes. In contrast to formation Caragana stenophylla-typical, the edificator species of native vegetation in formation Caragana stenophylla-desert mainly included Allium polyrhizum and Stipa tianschanica var. klemenzii. The mean vegetation height was 8.25 cm. The mean cover of the herb layer was 28%. Species numbers per m2 plot ranged from 4 to 14, with a mean of 8
, and the total number of species in the formation was 85. The most frequent species in this community species per releve included Caragana stenophylla, Artemisia sieversiana, Carex korshinskyi, Leymus secalinus, Salsola collina, Convolvulus ammannii, and Stipa sareptana var. krylovii. Other plant species in this formation were from the Chenopodium, Artemisia, Cleistogenes, and Astragalus. 4. Discussion 4.1. Floristic features of the Hulun Buir Steppe Life forms can be considered as a plant strategy in response to the hydrothermic gradient (Wang et al., 2002). In the Hulun Buir Steppe, hemicryptophytes represent the main life form, cryptophytes and therophytes account for a certain proportion, and chamaephytes and phanerophytes account for the least proportion. These features show that the environmental conditions of the Hulun Buir Steppe are much better than other grasslands on the Mongolian Plateau (Liu et al., 1994, 2014). Here, different vegetation types showed different characteristics of the life-form spectrum (Fig. 7-a, b, c). In the meadow steppe belt at the western foot of the Greater Khingan Mountains and the typical steppe belt in the eastern part of the Hulun Buir Steppe, the limitation of terrain conditions, under grazing stage, and a large number of dead branches and leaves accumulated on the surface, have resulted in loose soil and a deep humus layer, which is beneficial for the growth and development of hemicryptophytes and cryptophytes relying on vegetative reproduction. The occurrence of therophytes is associated with individual habitat conditions such as sandy land, saline-alkali land and abandoned wasteland, and it can also be explained by soil

Fig. 7. Floristic features in three vegetation types of Hulun Buir Steppe. Note, the full names of different abbreviations are the same as Figs. 2 and 3.

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disturbances, creating a suitable place for ruderals in this zone. Influenced by the climate of the vast Eurasian steppe, the proportion of chamaephytes and phanerophytes is the least, which also indicates that shrub encroachment in the Hulun Buir Steppe is relatively rare (CENMN, 1985; Liu et al., 2014). In desert steppes, hemicryptophytes are dominant, but the proportion of cryptophytes and therophytes is significantly higher than other vegetation types, mainly because in the desert steppe, cryptophagous plants are mostly bulbous or tuberous plants, which hide their buds in the ground to survive the harsh environment of low temperature in winter and drought in summer; The large proportion of annual plants indicates that this region is greatly impacted by rainfall, and when the environment is too dry, rainfall becomes the dominant controlling factor for annual plants in this region (CENMN, 1985; De C
aceres et al., 2015; Chen et al., 2014). Because the altitude of the Greater Khingan Mountains is not very high, the western low-mountains of the Greater Khingan Mountains and the forest-steppe transition belt are affected by the Pacific monsoon (the precipitation is 400e500 mm), which can form a semihumid forest and grassland climate that is suitable for the growth of mesophyte plants. The steppe region in the western Greater Khingan Mountains is mainly affected by the cold and dry air flow from Mongolia (the precipitation is 250e380 mm). Moreover, under the dual effects of the rain shadow effect and foehn wind effect, it forms a semihumid and semiarid grassland climate, which is suitable for the development of xerophytes (Zhang et al., 2011; Qu et al., 2018). Therefore, in the Hulun Buir Steppe, typical-mesophytes account for the absolute predominance, typicalxerophytes account for a small proportion, and other plant water ecotypes represent the smallest component. As shown in Fig. 7(d,e,f), in meadow and typical steppes, typical-mesophytes and hygro-mesophytes have an absolute advantage, indicating that the water conditions of typical and meadow steppes are significantly better than those of desert steppe, where typicalxerophytes and meso-xerophytes make up 73.33% of the total species, which is sufficient to explain the super xerophytic nature of the desert steppe flora. The main floristic geographic element of the Hulun Buir Steppe belongs to the East Paleo-Arctic Region, but the compositions of the Palaeo-Arctic, East Asia, Pan-Arctic and Siberia-East Asia elements also play an important role (Fig. 3). Concurrently, the Central Asia element also occupies a small component, mainly because the Hulun Buir Steppe borders the Mongolian grassland in the west and the grassland in the Dauria region of Russia in the north. Influenced by the Eurasian Steppe climate, it is located in the East Paleo-Arctic Region. The semihumid, semiarid continental climate of the western ridge results in a small concentration of the Middle Asia element (Wu, 1991; Wu et al., 2003, 2006; Zhao, 2012). This phenomenon fully supports that the modern ecological environment (precipitation and temperature) of the vegetation location is the primary reason for the peculiarity of the floristic features of the Hulun Buir Steppe. Different vegetation types show different floristic features (Fig. 7-g,h,i). In meadow steppe and typical steppe, East Palaeo-Arctic elements show an absolute dominance, among which the Mongolian Plateau element and Siberian-East Asian element occupy a very large proportion. The findings fully support that the flora of typical and meadow steppes is consistent that of the Mongolian Plateau steppe and the cold high latitudes of Siberia (ECVC , 1980; CENMN, 1985; Hilbig, 1997). In desert steppes, in addition to the dominance of the East Paleo-Arctic element, the Middle Asia element was found to be significantly more prominent than the other 2 vegetation types, indicating that the flora of the desert steppe is closely related to the desert areas in central Asia. In particular, the desert steppe of the Hulun Buir Steppe is connected to the eastern Mongolian dry steppe, which is one explanation for the large proportion of the central Asian component in this region (Hilbig, 1997). 4.2. Climatic drivers of vegetation distribution Vegetation types and their patterns are mainly controlled by geographical variables and climate conditions. Different geographical variables or different climate types have a set of corresponding vegetation types (Miehe et al., 2011). As demonstrated in studies in Eurasia, steppe vegetation is influenced mainly by altitude, longitude, topography, grazing intensity and soil fertility (Berman, 2001; Gadghiev et al., 2002; Ryabinina, 2003; Peer et al., 2008; Miehe et al., 2011). Austrheim (2002), in his study of seminatural grasslands, found a total richness per altitudinal zone that decreased with altitude belt plants, while small plots (0.25 m2) showed a mid-elevational peak below the timberline. These discrepancies indicate that different mechanisms are relevant for species richness with small and large grain sizes. The change in temperature and precipitation due to longitude or altitude is undoubtedly an important variable influencing the vegetation type (Zhong et al., 2010), but most previous studies have focused on the change in temperature due to altitude and neglected other changes, such as the change in precipitation due to longitude, because the biological effects of temperature are often better understood for most of the organisms examined (Lemmens et al., 2006; Zhou et al., 2017). Soil moisture is known to affect nutrient availability in various habitat types (Loiseau et al., 2005; Rodriguez-Iturbe et al., 1999). Water limitation reduces productivity because it reduces the ability of dominants to develop sufficient growth, even under nutrient-rich conditions. According to the available information, the overall plant diversity typically declines with decreasing water availability (Pausas and Austin, 2001). The topographically structured soil moisture is often considered the main controller of local plant diversity patterns in grasslands (Moeslund et al., 2013). However, patterns of water availability often covary with other ecological or geographical gradients, as the longitude gradient has the greatest influence on pre
et al., 2014). Although the main focus of this paper is on classification of vegetation types rather than the cipitation (Valko influence of environmental variables on the classification of vegetation types, we can still deduce, based on the literature analyzed above, that the most crucial factor determining both floristic features and vegetation structures in the Hulun Buir Steppe must be the change in precipitation due to longitude. Almost all community characteristics (including the herb layer cover, herb layer height and above-ground biomass) and the diversity index (including species richness, Shannon-Weiner

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index and Simpson index) show a significantly increasing trend with increasing latitude from approximately 116
E121
E in the Hulun Buir Steppe (Fig. 8 a, b, c, e, f, g), while the dissimilarity and Pielou index do not change significantly with the increase in longitude (Fig. 8 d, h). All of these results demonstrate that geographical variables significantly affect the distribution of vegetation types on the Hulun Buir Steppe, and the main geographical variable is the change in precipitation caused by the longitude gradient.

Fig. 8. Predicting pattern of cover of herb layer, height of herb layer, above-ground biomass, dissimilarity, species richness, Shannon-Weiner index, Simpson index and Pielou index in the whole study area from west to east longitude using a polynomial regression trend.

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4.3. Climatic factors affecting the distribution of vegetation types The distribution and coverage of natural vegetation are known to be strongly influenced by climate change (Wang et al., 2003; Bao et al., 2014). As focal factors, temperature and precipitation can influence the start and end of the growing period and vegetation activity (Zhang et al., 2017, 2019; Sun et al., 2010). Larger changes in vegetation distribution and structure occur in response to warming and especially in response to regional precipitation shifts (Wolfgang et al., 2001). The westerlies are an important components of the Eurasian climatic system, which not only impact the hydrological cycle over the Eurasian continent (An et al., 2012; Han et al., 2014) but also determine the dust entrainment, transport and deposition on the Eurasian continent as well as the Northern Hemisphere, generating a dramatic impact on regional solar and thermal radiation and cloud and precipitation processes (Gong and Chang, 2002; Huang et al., 2017; Xu et al., 2018). Climatically, local precipitation in Central Asia occurs when depressions, which develop over the eastern Mediterranean, introduce moist air to central Asia during late spring and summer along a northeast trajectory through the westerly circulation (Lioubimtseva et al., 2005). Water vapor can even be transported as far as the central and eastern Mongolian Plateau (Sato et al., 2007). The trajectory of the westerly circulation is therefore likely to be a major factor controlling moisture in the steppe region of the eastern Mongolian Plateau, and the trajectory of the westerly circulation is clearly mainly west-east (Chen et al., 2010). The Hulun Buir Steppe, located in the northeast margin of Mongolian Plateau with a longer distance from the Mediterranean Sea, is not controlled by westerlies (c2 in Fig. 9), in fact, it is controlled by Siberia High (SH) atmospheric pressure in winter (Chen et al., 2000; Gong and Chang, 2002), with dry and cold weather (Liu et al., 2019; Tong et al., 2018; Shinoda et al., 2010), and by the West Pacific Subtropical High (WPSH) in summer with moist and hot weather (Ding et al., 2015; Yang and Lu, 2014; Liu et al., 2019; Tong et al., 2018). The East Asian Winter Monsoon (EAWM) system and East Asian Summer Monsoon are the two most active components of the global climate system and the Asian climate system (Tao and Chen, 1987; Wang et al., 2000; He et al., 2007; Yang et al., 2017; Jin et al., 2019). In winter (Fig. 9-I), the robust Siberian High is the most important atmospheric center of action in

Fig. 9. Schematic diagramof atmospheric precipitation inHulun Buir Steppe.

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Eurasia, with a strong Aleutian Low (AL) to its east over the North Pacific (Gong and Chang, 2002; Wu and Wang, 2002). Under the influence of Siberian High and the westerlies (c2 in Fig. 9-I), the main wind direction of the East Asian Winter Monsoon (c1 in Fig. 9-I) is west to east in the Hulun Buir Steppe (Chen et al., 2000; Zhang et al., 2011; Dong et al., 2013). The west wind forms more winter snowfall (c4 in Fig. 9-I) in the western piedmont and top mountain area of the Greater Khingan Mountains (GKM) and forms large amounts of accumulated snow in the mountain forests (the accumulated snow does not begin to melt until June every year). The west wind crosses the Greater Khingan Mountains (c3 in Fig. 9-I) and forms the rain shadow region (Rs in Fig. 9-I) at the eastern foot of the Greater Khingan Mountains because of the foehn effect, resulting in rising temperatures, dry air and less snow (Corby, 1954; Smith, 1989; Qi and Fu, 1992; Qi, 1993). However, west winds in the western piedmont area and forest region of the Greater Khingan Mountains results in lower temperature and more snowfall (Qi, 1993; Zhang et al., 2011; Dong et al., 2013). Under the influence of the Western Pacific Subtropical High and Indian low (Chen et al., 1992; Murakami and Matsumoto, 1994; Ueda and Yasunari, 1996; Li et al., 2011, 2012, 2019), the westerlies (c2 in Fig. 9-II) are very weak, and the summer climate of the Hulun Buir Steppe is mainly affected by East Asian Summer Monsoon generated by Western Pacific Subtropical High. In spring and summer, East Asian Summer Monsoon (c1 in Fig. 9-II) passes over the Greater Khingan Mountains and forms the rain shadow (Rs in Fig. 9-II) in the west of the mountains. Concurrently, the foehn will also accelerate the ablation of snow accumulation in the forest at the western Greater Khingan Mountains, forming snowmelt
s et al., 2010; Jordan et al., 2019; Juraj et al., 2019). runoff (c5 in Fig. 9-II) (Corby, 1954; Liang et al., 2011; Tang et al., 2015; Andre The snowmelt runoff together with the summer rainfall (c4 in Fig. 9-II) formed by the East Asian Summer Monsoon in this region constitutes favorable climatic conditions for the formation of moisture in the meadow steppe (CENMN, 1985). However, as the distance from the Greater Khingan Mountains increases, the East Asian Summer Monsoon carries less water
s et al., 2010; Luo et al., 2014). In most vapor and less surface runoff from the Greater Khingan Mountains decreases (Andre western areas connected to the Dry Stipa Steppe in the East Mongolia Region of Mongolia, the desert steppe type is formed, and precipitation in this region is minimally affected by the East Asian Summer Monsoon, with an average annual precipitation of only 200 mm (Hilbig, 1997). Finally, as shown in Fig. 10, the plant community types of the Hulun Buir Steppe are diverse and can be conceptualized as meadow, typical and desert steppes along the Greater Khingan Range from east to west.

Fig. 10. Schematic diagram of Hulun Buir Steppe vegetation-type distribution.

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5. Conclusions In the Hulun Buir Steppe, which is one of the most globally famous grasslands in the Northern Temperate Zone, vegetation classifications were described systematically for the first time based on complete floristic data and community survey data. Our conclusions show the following. Among the 765 vascular plant taxa, the main plant group of all vascular plants in terms of species numbers are dicotyledons, followed by monocotyledons and pteridophyta, with gymnosperms having the smallest numbers. The life forms are dominated by hemicryptophytes, the water ecological types are dominated by typicalmesophytes, and the floristic geographical element is dominated by the East Palaeo-Arctic element. The vegetation types of the Hulun Buir Steppe were divided into 31 formations, which were grouped into three Vegetation-types and eleven Vegetation-subtypes. The plant community types were found to be diverse and could be conceptualized as meadow steppe, typical steppe and desert steppe along the Greater Khingan Range from east to west (Fig. 10). The vegetation types of the Hulun Buir Steppe are mainly affected by geographical variables and climatic factors; among geographical variables, it is mainly affected by the change in precipitation caused by the longitude gradient, whereas among climatic factors, it is mainly affected by the East Asian Winter Monsoon caused by the Siberian high and the East Asian Summer Monsoon caused by the Western Pacific Subtropical High. In addition, surface runoff caused by forest snowmelt and seasonal rainfall, as well as the distance from the Greater Khingan Mountains, also affect the distribution of the Hulun Buir Steppe vegetation. Acknowledgements This study was supported by the National Key Research and Development Program of China (Grant No. 2016YFC0500908), the International Science & Technology Cooperation Program of China (2015DFR31130), and the National Key Research and Development Program of China (Grant No. 2016YFC0500804). We are most grateful to Professor Zhao Liqing of Inner Mongolia University for identifying plant specimens for this study and providing photos of some vegetation types for this paper. References Amitai, R., Biran, M., 2005. Mongols, Turks, and Others: Eurasian Nomads and the Sedentary World. Brill, Lendon, The Netherlands. An, Z.S., Colman, S.M., Zhou, W.J., Li, X.Q., Brown, E.T., Timothy, Jull, et al., 2012. Interplay between the westerlies and asian monsoon recorded in lake qinghai sediments since 32 ka. Sci. Rep. 2, 619e625.
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