Abstract:

The analysis of the spatial distribution patterns and diversity characteristics of mountain plant communities in arid areas in response to an elevation gradient is helpful to explore the ecological adaptation strategies of mountain plants. TWINSPAN and DCA sequencing methods were used to study the distribution pattern and diversity of alpine grassland vegetation community on the north slope of Qilian Mountains. It was found that the alpine grassland vegetation in the Qilian Mountains could be divided into 9 categories， and with increasing elevation， the vegetation type changed from desert to desert steppe and then to typical steppe. Finally， there was a gradual transition to a meadow grassland. The key plant species associations in the elevational succession of vegetation categories were： a patchy distribution of associated Kalidium foliatum+Phyllanthus urinaria， transitioning to associated Ajania fruticulosa+P. urinaria， then associated Sympegma regelii+P. urinaria， an association of Caragana opulens+Achnatherum splendens， an association of Agropyron cristatum+Stipa sareptana， an association of S. sareptana+Leymus secalinus， gradually evolving into a Caragana jubata+Salix cupularis association， and eventually a Carex tristachya+Kobresia myosuroides association with mosaic distribution. The Shannon-Wiener diversity indexes （H'） and species richness indexes （R） of grassland communities generally showed ‘double peaks’； the Pielou evenness index （J） had highest values at mid altitudes， while the Simpson dominance index （C） had lowest values at mid altitudes. In summary， the vegetation types of the Qilian Mountains exhibited an elevational succession from low-altitude desert to high-altitude meadow grassland with associated changes in plant community distribution patterns and species composition， which reflected the filtering effect of the mountain environment on plant community construction.

Key words: species diversity, Qilian Mountain, plant community composition, elevation, TWINSPAN