Phytosociological studies in the Alashan Gobi - A contribution to the flora and vegetation of Inner Mongolia (NW China)
The study contributes to the knowledge of the semi-desert and desert communities of the southern Alashan Gobi (Ejina Qi area) and the montane slopes and foothills of the northern Qilian Shan, Beishan, and Ya Gan Mts. of northwestern China. It follows the traditional BRAUN-BLANQUET approach. Stone and gravel deserts are the most common and most impressive feature of the landscape, typical of the more or less flat and extended alluvial plains, terraces and depressions. In addition, dunes and aeolian sands occur, dominated by psammophytic phytocoenoses. Outstanding and very prominent is the Ruoshui river system, its inland delta and endorheic basins, which drains the whole area. As most parts of the area receive less than 60 mm rainfall per year, xerophytic semishrubs and dwarf-shrubs give a peculiar appearance to this desert. The zonal vegetation drastically changes from shrub semi-deserts and montane dwarf-shrub communities ( Sympegma montane steppe) in the surrounding mountains, to a very open desert steppe, dominated by dwarf-shrubs, such as Artemisia tschernieviana, Ephedra przewalskii, Nitraria sphaerocarpa, Reaumuria soongorica, and Zygophyllum xanthoxylon . Trees are a rarity and exclusively linked with the groundwater flow of the Ruoshui, where phreatophytes, such as Populus euphratica and Tamarix ramosissima, dominate the natural riparian woodland. Frequently intermixed are aeolian sands, dunes and salty depressions (solonchak formation) with various psammophytes [e. g., Calligonum mongolicum, Haloxylon ammodendron ('black saxaul')] and halophytes (e. g., Aeluropus littoralis var. sinensis, Kalidium foliatum, Salicornia perennans ). They form the azonal vegetation of the whole area. Grasslands ( Achnatherum splendens ) and marshes ( Phragmites reed) occur around flood plain depressions, stream sides and the endorheic basins, providing an important grazing resource for the local people and their life-stock. In total, five classes, six orders, six alliances, seven associations, three subassociations and eight rankless communities are treated for the first time from this part of China. Six of the units are described as new (viz., Asterothamno centrali-asiatici-Gymnocarpetum przewalskii, Nitrario sphaerocarpae-Artemisietum tschernievianae, with the subassociations typicum, lycietosum ruthenicae, and calligonetosum mongolicae, Salicornio perennantis-Aeluropetum sinensis, Halerpesto cymbalariae-Crypsietum aculeatae). They provide the basis for the comparison of the vegetation of the study area with the units described from the neighbouring Mongolia, which remain the single syntaxonomic reference for this part of Central Asia.