Psammophyte vegetation of the Khudan River valley (Republic of Buryatia)
Authors: Korolyuk A. Yu. 
Published: December 2023

Open sands in the Western Transbaikalia occupy large areas. Syntaxonomy of psammophytic vegetation has been developed for many regions of Baikal Siberia: the Selenga basin (Dulepova, Korolyuk, 2015), the Baikal coast (Brzeg, Wika, 2001; Chytrý et al., 1993; Dulepova, 2016), the Barguzin basin (Dulepova, Korolyuk, 2021), Verkhnecharskaya depression (Dulepova, Korolyuk, 2013). However, the sand vegetation in the Khudan River valley still was not studied. This area is interesting because it is remote and isolated from regions with wide distribution of sand dune vegetation. The objective of the study is to identify the diversity of psammophytic communities of the Khudan River valley and determine their syntaxonomical position.

The dataset includes 45 relevés of psammophytic communities performed by the author between Innokentievka and Mogsokhon villages, Kizhinginsky district of the Republic of Buryatia (Fig. 1). Data analysis was carried out using IBIS 7.2 (Zverev, 2007), Statsoft Statistica v.8.0 (Hill, Lewicki, 2007), and PAST 3.0 (Hammer et al., 2001). As a result of cluster analysis (Ward method, Sokal & Sneath similarity measure No. 1) the syntaxa of lowest ranks were identified (Fig. 3).

The class Brometea korotkiji Hilbig et Korolyuk 2000 unites the vegetation of open sands in East Siberian–Central Asian sector of the Palearctic (Lavrenko et al., 1988). Three species from its diagnostic combination were found in the Khudan valley: Bromopsis korotkiji, Carex sabulosa, Corispermum sibiricum. The order Oxytropidetalia lanatae Brzeg et Wika 2001 represents the psammophytic communities of Baikal Siberia. In the study area it is diagnosed by Oxytropis lanata and Chamaerhodos grandiflora. The range of the alliance Festucion dahuricae Dulepova et Korolyuk 2015 covers the Barguzin and the Selenga basins. In the analyzed relevés, Aconogonon sericeum, Agropyron michnoi, Artemisia xanthochroa, A. xylorhiza, Leymus littoralis, Festuca dahurica represent the diagnostic species of the alliance.

Communities of the ass. Corispermetum sibirici Gogoleva in Kononov ex Taran 1995 (Table, rel. 1, 2) form small patches along the gentle tops of dunes and ridges, more rarely on steep slopes and in deflation depressions (Fig. 4). Communities of the ass. Leymetum littoralis Dulepova et Korolyuk 2015 (Table, rel. 3, 4) occur in actively eroded habitats. The ass. Oxytropido lanatae–Caricetum sabulosae Dulepova et Korolyuk 2021 (Table, rel. 5) was found only once on flat sandy ridge (Fig. 5). Communities of the ass. Corispermo sibirici–Oxytropidetum lanatae Dulepova et Korolyuk 2015 are widespread on not fixed sands (Table, rel. 6–14). They occupy slopes, flat ridges and deflation depressions. The var. typica is characterized by domination of Oxytropis lanata and high abundance of Corispermum sibiricum. The var. festuca dahurica represents fescue sandy steppe with co-domination of Oxytropis lanata.

Association Aconogonetum sericei ass. nov. (Table, rel. 15–35). Holotypus – relevé 15 in Table (field no. 12-0720), Republic of Buryatia, Kizhinginsky district, south of the Ulzyte village, top of the sandy ridge, 16.08.2012, Korolyuk A. Yu.

Diagnostic species: Aconogonon sericeum, Bromopsis korotkiji.

Association represents the most widespread psammophytic communities in the Khudan valley (Fig. 6). The projective cover varies from 15 to 30 %, species richness — from 4 to 16 species per relevé. These features depend on anthropogenic pressure and wind erosion. The main dominant is Aconogonon sericeum. Some species occasionally demonstrate high abundance: Leymus littoralis, Artemisia xylorhiza, Oxytropis lanata, Bromopsis korotkiji.

Class Cleistogenetea squarrosae Mirk. et al. 1985 includes the steppe communities of the East Siberian-Central Asian type. The order Stipetalia krylovii Kononov et al. 1985 and the alliance Stipion krylovii Kononov et al. 1985 represent typical steppes. The diagnostic combinations of these syntaxa are represented by some species occurring in the studied psammophytic communities: Agropyron cristatum, Artemisia frigida, Carex duriuscula, C. korshinskyi, Chamaerhodos erecta, Dontostemon integrifolius, Heteropappus altaicus, Koeleria cristata, Poa botryoides, Potentilla bifurca, P. tanacetifolia, Pulsatilla turczaninovii, Serratula centauroides.

The community Thymus baicalensis (Table, rel. 39–44) was described on leveled sandy habitats between open sands and steppes or shrubs. Thymus baicalensis is the main dominant, occasionally Leymus littoralis and Aconogonon sericeum co-dominate.

The psammophytic vegetation of the Khudan valley is characterized by high diversity. An anthropogenic pressure contribute significantly to the exodynamic successions. Increased grazing results in the dominant life forms changes as following: shrubs and trees → bunchgrasses → taproot perennial grasses and semi-shrubs → rhizomatous plants → annual plants (Dulepova, 2012). The NMDS-ordination shows strong relation between species composition and community’ structure, succession state and coverage of different life forms (Fig. 7). The first axis on the scatter plot is related to the ratio of annuals and perennials. The second axis reflects the ratio of mobile (rhizomatous perennials) and immobile (taproot perennials, bunchgrasses, semi-shrubs) species.

The studied communities represent a part of a psammophytic complex of the Selenga basin as a whole. This is reflected in the unity of the flora and the existence of associations found both in the Selenga and Khudan valleys. The only ass. Aconogonetum sericei ass. nov. is confined to the Kizhinginsky district. In terms of phytocenotic diversity, the psammophytic vegetation of the Khudan River valley is poorer in comparison with the middle part of the Selenga basin.