Steppes of the class Cleistogenetea squarrosae Mirkin et al. ex Korotkov et al. 1991 in Eastern Transbaikalia

Transbaikalia is the vast region in Southern Siberia which includes numerous mountain ridges within the upper basins of the three big rivers, the Amur (Pacific Ocean basin), the Yenisey, and the Lena (Arctic Ocean basin). The most part of Transbaikalia territory is covered by woodlands, however, the steppes are an inherent component in the southern part of the region. Due to broad distribution they form the steppe and forest-steppe altitudinal belts in the mountains, and even totally predominate in the vast plains of the southeastern part of studied territory. Steppe communities occur throughout the broad range of habitats varying in humidity, edaphic conditions, and anthropogenic disturbance.

There is a lack of any established opinion on Transbaikalian steppe classification among the Russian botanists (Reshchikov, 1961; Lavrenko et al., 1991; Dulepova, 1993). The syntaxonomy of east-transbaikalian steppes has not been developed yet. The steppes of this region are represented in few publications covering small territories. T. L. Arbuzova and B. I. Dulepova (1989) described three associations from the Sokhondo Biosphere Reserve, which were attributed to the class Cleistogeneta squarrosae Mirkin et al. ex Korotkov et al. 1991.

The main aims of my study are: (1) to propose a phytosociological classification of east-transbaikalian steppes and to characterize the syntaxa distinguished, (2) to reveal principal ecological factors that have an influence on regional syntaxonomical patterns of the steppe vegetation in Transbaikalia.

All transbaikalian steppes belong to the class Cleistogenetea squarrosae. The class represents main dry grassland diversity of the East Siberian–Central Asian sector of Palaearctic (Hilbig, 1995; Korolyuk, 2002). This class consists of two orders: Helictotrichetalia sсhellianiHilbig 2000 (meadow steppes and rich-in-species bunchgrass steppes of mountain forest-steppe), and Stipetalia krylovii Kononov, Gogoleva et Mironova 1985 (typical bunchgrass steppes of the steppe zone and mountain steppe belt).

AllianceStipion krylovii includes non-petrophytic steppes which are common mainly in the steppe belt and the steppe zone. In Eastern Transbaikalia it is represented by two associations. Ass. Potentillo semiglabrae–Stipetum grandisass. nov. (Table 1; holotypus hoc loco — relevé 4 (09-349): Trans-Baikal Territory, Ononskiy district, north coast of Zun-Torey Lake, N 50.16447°, E 115.84509°, 22.07.2009, author — A. Yu. Korolyuk) is common in south-eastern part of Trans-Baikal Territory and in the adjacent regions of Mongolia. It unites more xerophytic variants of zonal steppes dominated by bunchgrasses and rhizomatous Leymus chinensis. Ass. Artemisio laciniatae–Leymetum chinensis ass. nov. (Table 1; holotypus hoc loco — relevé 13 (09-436), Trans-Baikal Territory, Ononskiy district, Daurskiy Nature Reserve, the plain between Nizhniy Mukey Lake and Imalka River, N 49.99331°, E 115.25308°, 29.07.2009, author — A. Yu. Korolyuk) includes typical steppes which are developed on soils under occasionally influence of ground waters. It causes low salinization of the upper soil horizons and high frequency and abundance of salt tolerant plants — caespitose Iris lactea and rhizomatous Leymus chinensis, Thermopsis lanceolata, Artemisia laciniata.

AllianceThymion gobici Mirkin et al. ex Hilbig 2000 comprises xerophytic petrophyte steppes of Transbaikalia, Central and Eastern Mongolia, Inner Mongolia province (China). In Eastern Transbaikalia it is represented by single ass. Ptilotricho dahurici–Arctogerontetum graminei ass. nov. (Table 1; holotypus hoc loco — relevé 29 (09-327), Trans-Baikal Territory, Aginskiy district, west coast of Nozhiy Lake, N 50.83191°, E 114.80023°, 21.07.2009, author — A. Yu. Korolyuk).Into this association, I includes polydominant rich xerophytic petrophyte steppes that are characterized by high abundance of short-growing perennial herbs, often with cushion growth form.

OrderHelictotrichetalia schellianicomprises meso-xerophytic grasslands, mainly meadow steppes of East Siberian–Central Asian sector of Palaearctic. It unites the most widespread non forest plant communities of forest-steppe landscapes. The area of the order extends considerably to the north in comparison with the order Stipetalia krylovii.

AlliancePotentillion acervatae all. nov. (holotypus — ass. Thalictro appendiculati–Stipetum baicalensisass. nov. hoc loco) represents the meadow steppes and sometimes xeric meadows of Eastern Transbaikalia. It comprises zonal meadow steppes and petrophytic steppes which we have attributed to two new suballiances.

The central suballiance Potentillenion acervatae suball. nov. (holotypus — ass. Thalictro appendiculati–Stipetum baicalensis) represents meadow steppes on fine soils. Ass. Bupleuro scorzonerifolii–Gypsophiletum davuricae ass. nov. (Table 2; holotypus hoc loco — relevé 11 (09-439), Trans-Baikal Territory, Ononskiy district, 10 km to the N from Krasnaya Imalka village, N 50.361°, E 115.292°, 30.07.2009, author — A. Yu. Korolyuk) is widespread both in the forest-steppe and steppe belts. Ass. Thalictro appendiculati–Stipetum baicalensisass. nov. (Table 2; holotypus hoc loco — relevé 18 (08-310), Trans-Baikal Territory, Priargunskiy district, to the E from Klichka settlement, urotshistshe Soldatskaya Pad, N 50.45168°, E 118.05152°, 19.07.2008, author — A. Yu. Korolyuk) comprises floristically rich and polydominant meadow steppes representing one of the dominating vegetation types of the forest-steppe belt. Their feature is the absence of steppe xerophytes of the class diagnostic combination among abundant species. The physiognomy of some communities of the association reminds the xeric meadows. Ass. Bupleuro scorzonerifolii–Iridetum lacteaeass. nov. (Table 2; holotypus hoc loco — relevé 30 (09-422), Trans-Baikal Territory, Ononskiy district, Daurskiy Nature Reserve, east coast of Bulun-Tsagan (Sataninskoye) Lake, N 50.11519°, E 115.12766°, 29.07.2009, author — A. Yu. Korolyuk) represents the variants of meadow steppes developing on slightly salinizated soils. The community physiognomy is determined by predomination of the salt-tolerant rhizomatous grass Leymus chinensis.

The suballiance Scutellarienion baicalensis suball. nov. (holotypus — ass. Potentillo acervatae–Festucetum lenensisass. nov. hoc loco) comprises petrophytic steppes of Eastern Transbaikalia. The central ass. Potentillo acervatae–Festucetum lenensis(Table 3; holotypus hoc loco — relevé 4 (08-221), Trans-Baikal Territory, Karymskiy district, 5–7 km to the N from Urulga village, N 51.82546°, E 114.80403°, 07.07.2008, author — A. Yu. Koro­lyuk) dominates on stony habitats in the forest-steppe belt and is widespread in the steppe belt. The basic dominant of association is Filifolium sibiricum.Ass. Scutellario baicalensis–Vicietum popoviiass. nov. (Table 3; holotypus hoc loco — relevé 15 (08-257), Trans-Baikal Territory, Nerchinsko-Zavodskiy district, to the NE from Solonechnaya village, N 51.41797°, E 119.66385°, 13.07.2008, author — A. Yu. Korolyuk) combines the more moist communities of petrophytic meadow steppes which are widespread in the forest-steppe landscapes. Like in previous association, the main dominant is Filifolium sibiricum. However, mesoxerophytes also prevail among abundant species. Ass. Allio prostrati–Pulsatilletum tenuilobaeass. nov. (Table 3; holotypus hoc loco — relevé 25 (09-441), Trans-Baikal Territory, Borzinskiy district, 7–8 km to the N from Tasyrkhoy village, Adun-Cholon Mountains, N 50.47951°, E 116.09508°, 31.07.2009, author — A. Yu. Korolyuk) represents short-growing petrophytic steppes. Ass. Festuco lenensis–Caraganetum microphyllae ass. nov. (Table 3; holotypus hoc loco — relevé 46 (12-0852), Trans-Baikal Territory, Aginskiy district, 9 km to the SE from Orlovskiy settlement, N 50.99271°, E 115.05677°, 24.08.2012, author — A. Yu. Korolyuk) unites more mesophytic variants of petrophyte steppes, which are widespread mainly in the steppe belt. Some petrophytes from the diagnostic combination of the suballiance have lower occurrence here and usually are not abundant. Physiognomically the communities are close to zonal steppes, however, the petrophytic group is well represented in these.

Strong geographical and ecological gradients have been revealed by the numerical analysis of associations of transbaikalian steppes (Korolyuk, 2017). On the first axis of NMDS-ordination (Fig. 8) all associations were split up into two geographical groups: west- and east-transbaikalian ones. This is a consequence of obvious distinction between steppe floras of two basins belonging to the Pacific and Arctic Oceans. In general, the first axis is correlated with climatic gradients. For instance, from the west eastwards in Transbaikalia, parameters of temperature and precipitation seasonality are increasing, while annual mean temperature and precipitation are reducing. The second axis is correlated with moisture which is determined by precipitation, and the soil moisture that depends on landform features as well.

The third axis is the most likely of complex character. The associations of the petrophytic alliance Thymion gobici and two vicariant petrophytic suballiances occupy the upper part of the ordination scatterplot. In the central part of the third axis there are communities forming on various soils of plains and foreslopes, as well as on concave parts of slopes. On the third axis petrophytic steppes are allocated in the opposite position to the steppe communities in which shrubs are abundant (Spiraeion aquilegifoliae Hilbig 2000 and Carici pediformis–Spiraeetum aquilegifoliae Korolyuk 2017). All of these communities are mainly confined to insolated southern slopes and foothills, both are of straight or concave shape. Large rocky debris and outcrop patches are typical. These habitats, as compared to convex summits and slopes, are well protected from winds that have a strong cooling and drying up effect.

The third axis has been interpreted as correlated with several ecological factors. By grouping petrophytic steppes in the upper part of the scatterplot the relation with the soil stoniness have been shown. In this direction the content of small rocky debris (r1) is increased. Downwards, communities of shrubby steppes have been grouped together. Two environmental factors, namely the incoming radiation (rad) and presence of large rocky debris and bedrock outcrops (r2) are of the most significant for these communities.

Three ecological groups of plants (steppe xerophytes, meadow steppe mesoxerophytes, and meadow-forest xeromesophytes and mesophytes) contribute to variability in the steppe vegetation in regards with moisture conditions. Affects of other environmental factors have been resulted in assembling plants into edaphically conditioned groups. Those groups indicate variability of stone, sand and salt content in soils. There is also a clear geographical pattern in the steppe vegetation associated with the longitudinal gradient.

Factors mentioned above are not related with each other. At the same time, they form strong environmental gradients determining multi-dimensional variability of the steppe vegetation. Numerous independent gradients make complicated elaboration of the hierarchical system. Depending on which factor is taken into account as a leading one, several approaches to classification could be developed. In the present study, the moisture conditions have been assigned as the most significant insofar as this factor reflects the major geographical pattern, namely latitudinal (zonal) differentiation of the steppe vegetation.

Due to interlacement of various environmental gradients resulting in high variability of habitats and consequent vegetation patterns, Transbaikalia is one of the most interesting regions of Inner Asia. The steppe vegetation here possesses the high diversity of flora and plant communities. Analysis of the large data set allowed me to develop the classification system of the transbaikalian steppe vegetation (Table 4). The following main principles in this system have been assigned.

All of transbaikalian steppes belong to the class Cleistogenetea squarrosae.

The moisture conditions are most important in differentiation of steppe vegetation of Transbaikalia. Two orders, namely Helictotrichetalia schelliani comprising meadow steppesandStipetalia krylovii representing typical steppes, have been distinguished along the moisture gradient.

Significant differences between floristic compositions of the meadow steppes in Eastern Transbaikalia from the one side, and Western Transbaikalia from the other one have been emphasized. According to these differences the meadow steppes of Transbaikalia were attributed to two vicariant alliances: Helictotrichion schelliani(Western Transbaikalia) and Potentillion acervatae (Eastern Transbaikalia).

Despite, typical steppes in Western and Eastern Transbaikalia floristically are much more similar to each other. This is the reason why I consider typical steppes within the single order Stipetalia krylovii, and no vicariant alliances have been distinguished within. All zonal steppe communities within the order have been attributed to the single alliance Stipion krylovii. Floristic differences between two other alliances within the order have been determined by the disparity of edaphic conditions.

Prevalence of the stony habitats throughout the whole region of Transbaikalia is resulted in the wide distribution of petrophytic steppes. A high number of associations, which have been united into alliance Thymion gobici (typical steppes) and is differed within as two suballiances in meadow steppes — Thymenion baicalensis Korolyuk 2017and Scutellarienion baicalensis.

Existence of xerophytic shrubby communities confined to well insolated slopes with large stone debris and bedrock outcrops are designated. These communities have been related to the single alliance Spiraeion aquilegifoliae that is widespread in territories of Transbaikalia and Northern Mongolia.

Further development of the dry grassland syntaxonomy of Inner Asia could be advanced by the involvement of the data from the territories of People′s Republic of Mongolia (Outer Mongolia) and the province of Inner Mongolia in China. This will allow to delineate the distribution of syntaxa, as well as to make a general revision of the class Cleistogenetea squarro­sae all over its distribution area.

Key words: steppe vegetation, syntaxonomy, environmental factors, ordination, Transbaikalia, Cleistogenetea squarrosae

Section: Articles

How to cite

Korolyuk A. Yu. 2019. Steppes of the class Cleistogenetea squarrosae Mirkin et al. ex Korotkov et al. 1991 in Eastern Transbaikalia // Vegetation of Russia. N 35. P. 28–60. https://doi.org/10.31111/vegrus/2019.35.28

Received April 26 2018

References

Supplementary materials

Electronic supplement 1. Association characterizing tables
VEG_RUS_KOROLYUK_2019_35_SUPPL_1

Electronic supplement 2. The locations of relevés
VEG_RUS_KOROLYUK_2019_35_SUPPL_2

Electronic supplement 3. Maps of locations of associations in Eastern Transbaikalia
VEG_RUS_KOROLYUK_2019_35_SUPPL_3