Classification of steppe vegetation in the eastern Pamir Alai and southwestern Tian-Shan Mountains (Tajikistan, Kyrgyzstan)

摘要

Aims: To complete the syntaxonomical scheme for the steppe vegetation of the montane and alpine zones in the Pamir Alai and southwestern Tian-Shan Mountains in Tajikistan and Kyrgyzstan with some remarks on its environmental predictors. Location: Tajikistan and Kyrgyzstan. Methods: A total of 274 releves were sampled in 2016-2017 using the seven-degree cover-abundance scale of Braun-Blanquet. They were classified with modified TWINSPAN with cut-off levels of 0%, 5%, 10% and 25% and total inertia as a measure of cluster heterogeneity. Diagnostic species were identified using the phi coefficient as a fidelity measure. Detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used to explore the relationships between groups in the dataset and to determine the environmental gradients that predict the species composition and distributional patterns of particular communities. Results: A total of 11 steppe communities were distinguished for the study area, grouped in five alliances and three orders. Seven of them are defined as new associations: Astragalo chomutowii-Stipetum subsessiliflorae, Stipetum bungeanae, Convolvuletum spiniferi, Stipo magnificae-Otostegietum olgae, Littledaleo alaicae-Stipetum trichoidis, Helictotricho fedtschenkoi-Stipeturn kirghisori and Astragalo lithophili-Sdpetum zalesskii. The communities belong to the Piptathero gradlis-Artemision brevifoliae (high-altitude, cold arid plateaus) and Ajanio-Cleistogenenion songoricae (alpine arid mountainous areas; both Ajanio-Cleistogenetea songoricae), the Poo bulbosae-Artemision persicae related to warm montane-subalpine belts of the southern part of Middle Asia (Astragalo microcephali-Brometea tomentelli, Carici stenophylloidis-Stipetalia arabicae) and the Stipion krylovii, typical steppes in semi-arid subalpine and alpine belts (Stipetalia krylovii, Cleistogeneta squarrosae). Within the Stipetalia krylovii, the TWINSPAN revealed a second unit at alliance level next to the Stipion krylovii, with currently only one association, but due to the limited amount of data we refrained from making a formal description. The main factors responsible for the species composition of the researched vegetation were altitude, content of organic top soil, and longitudinal position. Conclusions: We have completed the vegetation survey of the steppes in the middle and western part of Central Asia and have fostered the progress in finding the borderland between the steppes of the western Asiatic and central Asiatic subregions. This geographic transition corresponds to a syntaxanomic division between the classes of Astragalo microcephali-Brometea tomentelli Quezel 1973 and Cleistogenetea squarrosae Mirkin et al. ex Korotkov et al. 1991.