Syntaxonomy of steppe plant communities on the permafrost soils on the Vitimskoye Plateau (Transbaikalia region)
Authors: Anenkhonov O. A. , Naidanov B. B. 
Published: July 2024

There is a lot of studies concerning steppe vegetation in the Transbaikalia region, though detailed floristic classification has been developed recently (Korolyuk, 2017, 2019). However, some of the specific types of steppe communities are still out of that classification so far. In particular, meadow steppe communities on permafrost soils at the northern part of the forest-steppe subzone on the Vitimskoye Plateau (Transbaikalia) still are not classified. The paper aims to design the syntaxonomic position and brief characteristics of this particular vegetation. Rather similar communities are known as cryoxerophytic steppes from more northern regions (Yurtsev, 1978). Taking into account that studied area is slightly less cold we call Tranbaikalian meadow steppe communities on permafrost soils as hemicryomesoxerophytic steppe.

Our studies have been carried out within the Eravninskaya depression (Fig. 1) in the southwest of the Vitimskoye Plateau (Transbaikalia). The depression of hollow-concave shape with flat relief extends for about 80 km to the northeast, while the width is about 63.5 km, and elevation is about 950 m a. s. l. The climate is sharply continental, with frosty snowless winters and short and warm summers. The permafrost is common throughout the depression. The mean annual precipitation is 250–400 mm, with 60 % of the total amount falls in July–August. The main types of soils are represented by permafrost chernozem and turf soil (Badmayev et al., 2006). Meadow steppe in combination with the Gmelin larch and white birch coppices form the forest-steppe landscape.

Field studies have been conducted in 2009 and 2018, and 26 relevés (of 100 m2) of steppe communities were collected. The Braun-Blanquet approach for the classification of vegetation has been applied, and the nomenclature of syntaxa follows to ICPN (Theurillat et al., 2021).

Steppe vegetation of the south-west of Vitimskoye Plateau belongs to the class of Cleistogenetea squarrosae Mirkin et al. ex Korotkov et al. 1991, order Helictotrichetalia schelliani Hilbig 2000, and alliance Helictotrichion schelliani Hilbig 2000. Habitats of hemicryomesoxerophytic steppe communities differ from those of suballiances described within the Helictotrichion schelliani in relation to position across landforms and the soil profile pattern. Differences are noticeable contrast to habitats of the Thymenion baicalensis Korolyuk 2017 communities, and are less pronounced compare to those of the Stipenion baicalensis Korolyuk 2017. The special peculiarity of the floristic composition of hemicryomesoxerophytic steppes is imparted by the presence of Kobresia filifolia, K. myosuroides and Thalictrum alpinum, indicating the cryophilic habitats. Moreover, there is a set of montane-steppe species also evidencing the same environment situation. Based on the floristic composition (Table) and ecological specificity we describe a new suballiance of steppe vegetation, containing 2 new associations.

The suballiance Leontopodio conglobati–Caricenion pediformis Anenkhonov suball. nov. Nomenclatural type of the suballiance (holotypus) — ass. Kobresio filifoliae–Festucetum lenensis Anenkhonov et Naidanov. Diagnostic species (d. s.): Bistorta alopecuroides, Bupleurum sibiricum, Festuca lenensis, Gentiana decumbens, Leontopodium conglobatum, Lychnis sibirica, Rumex acetosa, Salix kochiana, Tephroseris integrifolia, Thalictrum alpinum.

The suballiance represents hemicryomesoxerophytic steppe communities confined to the permafrost soils in the cold and sharply continental climate in the northern part of the forest-steppe subzone of the Transbaikalia region. The suballiance communities occupy flatland habitats and produce the forest-steppe landscape in combination with larch (Larix gmelinii) or birch (Betula platyphylla) coppices. Less often these communities are confined to the southern slopes when forest dominates in the landscape.

The floristic composition of the hemicryomesoxerophytic steppes is significantly different from that of the cryophytic steppes described in other regions. Particularly, there are sufficient differences comparing to cryoxerophytic steppe of the Altai mountains, the subalpine montane steppe and kobrezian communities of Mongolia, and meadow-steppe communities in northern areas of Yakutia and West Chukotka. All of this support establishing the new syntaxon to integrate the hemicryomesoxerophytic steppe of Vitimskoye Plateau into the syntaxonomy of steppe vegetation. Defining the rank of the Transbaikalian hemicryomesoxerophytic steppes was based on the specificity of habitats, especially confinement to permafrost soils. Such criterion clearly separates these communities from steppes of the alliance Stipenion baicalensis, which are developed on seasonally frozen soils.

The suballiance includes 2 associations: (1) Kobresio filifoliae–Festucetum lenensis — relatively more cryophytic; (2) Orostachyo malacophyllae–Festucetum lenensis — relatively more thermophytic.

Ass. Kobresio filifoliae–Festucetum lenensis Anenkhonov et Naidanov ass. nov. (Table, rel. 1–15, Fig. 2).

Nomenclatural type (holotypus hoc loco): Table, rel. 4 (field number nb18-23), Republic of Buryatia, Eravninskiy district, 43 km NE Sosnovo-Ozerskoye village, 52.82825° N, 111.93925° E, Varioherbosae-Sedge-Kobresia meadow steppe, 10.07.2018. Authors — B. B. Naidanov, O. A. Anenkhonov.

D. s.: Artemisia rupestris, Equisetum arvense, Galatella dahurica, Heteropappus altaicus, Ixeridium gramineum, Kobresia filifolia, K. myosuroides, Potentilla anserina, P. arenosa.

The association represents hemicryomesoxerophytic steppe communities on meadow-chernozem permafrost soils. The habitats are relatively more cryophytic (comparing to the 2nd association). Communities usually occupy open flatlands or slightly concaved surfaces of various configurations, and also cover shady (the most often northerly and easterly) sites close to coppices.

Ass. Orostachyo malacophyllae–Festucetum lenensis Anenkhonov et Naidanov ass. nov. (Table, rel. 16–26; Fig. 3).

Nomenclatural type (holotypus): Table 1, rel. 20 (field number nb18-22), Republic of Buryatia, Eravninskiy district, 36 km NE Sosnovo-Ozerskoye village, 3.3 km SSE Khorga settlement, 52.78897° N, 111.84138° E, Varioherbosae-Fesque-Pasqueflower meadow steppe, 10.07.2018. Authors — B. B. Naidanov, O. A. Anenkhonov.

D. s.: Aconogonon angustifolium, Achillea asiatica, Campanula glomerata, Dianthus versicolor, Orostachys malacophylla, Schizonepeta multifida, Silene jeniseensis, Veronica incana.

This association, like a previous one, represents hemicryomesoxerophytic steppe communities, however, it is relatively more thermo- and xerophytic. Communities occur on slightly elevated flat surfaces, hillocks, sites on well–warmed forest edges – most often from the southern and western sides of coppices, and on southern and south-western slopes of hills.

To resume, hemicryomesoxerophytic steppe communities of Eravninskaya depression on the south-west of Vitimskoye Plateau represent a peculiar type of steppe vegetation, originated due to special habitats on the permafrost soils at the northern part of the main area of steppe vegetation in Transbaikalia region. These steppe communities belong to the new suballiance (with two new associations) of steppe vegetation.