Psammophyte vegetation of the Selenga river basin (Republic of Buryatia)

Modern aeolian relief is widespread in the forest-steppe landscapes of Transbaikalia. Valleys of the Selenga River and its inflows are the areas covered by ancient sandy deposits. Human impact in dry climatic conditions causes intensive wind erosion and formation of open and moving sands covered with sparse plants. The flora and vegetation of such landscapes notably differ from surrounding territories. It’s particularity is caused by presence and domination of plant species usually seen on open sands. Despite of numerous publications describing the sandy dunes of Transbaikalia, the psammophyte vegetation and natural dynamics of sandy landscapes are poorly documented.

This study presents the analysis of 398 relevés describing psammophyte vegetation from the South-West Transbaikalia (Selenginsky, Dzhidinsky, Kyakhtinsky and Bichursky administrative disticts of the Republic of Buryatia).

The sand dune vegetation in the Selenga River basin belongs to the class Brometea korotkyi Hilbig et Koroljuk 2000 and the order Oxytropidetalia lanatae Brzeg et Wika 2001. All differential species of the class Brometea korotkyi such as Bromopsis korotkiji, Carex sabulosa, Corispermum sibiricum, Hedysarum fruticosum, Leymus racemosus subsp. crassinervius are presented in the most of sandy massifs. Among species of diagnostic combination of the order Oxytropidetalia lanatae can be recognized: Agropyron michnoi, Artemisia ledebouriana, Leymus littoralis, Oxytropis lanata. They are the main dominants of psammophyte plant communities.

Comparison of our materials with data on psammophyte vegetation of Lake Baikal coasts (the alliance Oxytropidion lanatae) and the Chara River valley (the alliance Aconogonion chlorochryseum) has shown that the sand dune communities of the Selenga River basin differ in high activity of obligate (Festuca dahurica, Aconogonon sericeum) and facultative psammophytes (Artemisia xylorhiza, A. xanthochroa, Ulmus pumila) (Chytry et al., 1993; Dulepova, Korolyuk, 2013). In comparison with the corresponding communities from Chara and Baikal areas, described vegetation is differentiated by the occurrence of xerophyte species that are common to mountain forest-steppe landscapes: Cleistogenes squarrosa, Thymus baicalensis, Serratula centauroides, Carex korshinskyi, Thermopsis lanceolata, etc. Many of these plants are used in the diagnosis of the class Cleistogenetea squarrosae, the order Stipetalia krylovii and the alliance Stipion krylovii.

We described the new alliance Festucion dahuricae that unites psammophyte vegetation recorded from the Selenga River basin. Its diagnostic combination includes Aconogonon sericeum, Artemisia xanthochroa, A. xylorhiza, Festuca dahurica, Ulmus pumila. Within this alliance, we distinguished two associations (Corispermo sibirici–Oxytropidetum lanatae, Agropyro michnoi–Vicietum tsydenii) and Salix microstachya community.

The class Cleistogenetea squarrosae, order Stipetalia krylovii and alliance Stipion krylovii represent sandy steppes that are characterized by high frequencies and abundance of bunchgrass plants (association Cleistogeno squarrosae–Festucetum dahuricae and community Hippophaё rhamnoides).

The Malkhan-Elysun sandy massif is the biggest in Transbaikalia (about 11 km²) and it is surrounded by the dry pine forests. Uniqueness of this territory is due to its ancient origin. Only here two species with disjunctive areas are found (Republic of Buryatia and the Republic of Tyva) — Thesium tuvense and Corispermum macrocarpum. Vegetation of the Malkhan-Elysun sands also is distinguished by high frequencies of Linum sibiricum, Scorzonera radiata, Silene jeniseensis and Aconogonon sericeum. This sand massif is represented by two associations (Thesio tuvense–Festucetum dahuricae, Corispermo macrocarpi–Leymetum crassinervii), 2 subassociations (C. m.–L. c. typicum, C. m.–L. c. hedysaretosum fruticosi) and 3 communities (Padus avium, Populus laurifolia and Salix microstachya).

Natural dynamics of sand dune vegetation in the Selenga River basin is presented by two chronosequences. The first one is common for massifs that are surrounded by steppes: Corispermetum sibirici → Leymetum crassinervii; Leymetum littoralis; Agropyro michnoi–Vicietum tsydenii → Corispermo sibirici–Oxytropidetum lanatae → communities Salix microstachya, Hippophaё rhamnoides; Cleistogeno squarrosae–Festucetum dahuricae → bunchgrass steppe. The second one has been only observed in the Malkhan-Elysun sands: Corispermo macrocarpi–Leymetum crassinervii → Thesio tuvense–Festucetum dahuricae → communities Padus avium, Populus laurifolia and Salix microstachya → dry pine forest.

Natural and anthropogenic dynamic of psammophyte vegetation lead to origin of open sands with poor communities dominated by the species with wide distribution. The associations designated by the differential species of the class Brometea korotkyi (ass. Corispermetum sibirici, ass. Leymetum crassinervii) and the order Oxytropidetalia lanatae (ass. Leymetum littoralis) are widespread in the Selenga River basin. We consider that these monodominant communities can be included to alliances and order of the central type which are diagnosed by species of higher rank syntaxons. They can’t be included to the earlier described order Brometalia korotkyi Hilbig et Koroljuk 2000 from the territory the Republic of Tyva which is diagnosed by the species that are absent in Transbaikalia: Artemisia tomentella, Corispermum mongolicum, Pugionum pterocarpum etc. (Hilbig, Korolyuk, 2000).