Endemic formation of stitchwort polster (Stellaria pulvinata Grub.) in highlands of the Mongolian Altai

Abstract

Stitchwort polster (Stellaria pulvinata Grub.) is an endemic species with local distribution in the arid regions of Central Asia—the Mongolian Altai highlands (2500–3800 m above sea level). This species forms an endemic alpine cryophyte-herb-polster formation that is divided into three classes and ten groups of associations. Stitchwort is dominant and codominant in cryophyte-herb polster communities. In cryophyte-herb-sedge-kobresia polster communities, this species changes its presence from significant to minor, with moderate abundance. Cryophyte-herb-gramineous polster communities are widespread and have the highest coenotic diversity. Cryopetrophyte polster communities with Stellaria pulvinata play an important role in the vegetation cover of the central part of Mongolian Altai. They do not form a separate high-rise belt but are found in the composition of the vegetation cover of two high-rise belts, the cryophype bunchgrass steppe belt (2800–3200 m) and the cryophyte kobresia and sedge tundra belt (3200–3500 m). They are also sporadically found in the subnival belt (3500–3800 m). At the level of microcombinations, the vegetation cover structure contains serial ranks of polster communities on the mountainsides and polster complexes with herb-gramineous communities on the peneplanation surfaces and alpine moraines. Exposition combinations of phytocatenae with cryophyte-herb polster communities and cryophyte-bunchgrass steppes with stitchwort occur at the level of meso-combinations.