Syntaxonomic classification of forb steppes and related vegetation of subalpine and alpine belts in the Pamir-Alai Mountains (Tajikistan, Middle Asia)

Abstract

Aims: To complete the syntaxonomic scheme of subalpine forb steppes in the Pamir-Alai Mountains in Tajikistan with some remarks on its environmental predictors. Study area: Tajikistan. Methods: A total of 149 relevés were sampled in 2014 and 2021 using the seven-degree cover-abundance scale of the Braun-Blanquet scheme. These were classified with a modified TWINSPAN algorithm with pseudospecies cut-off levels of 0%, 2%, 5% and 25%, and total inertia as a measure of cluster heterogeneity. Diagnostic species were determined using the phi coefficient as a fidelity measure. Detrended Correspondence Analysis (DCA) was used to show compositional differences between the distinguished alpine and subalpine grassland units. Results: Our classification revealed 12 clusters of alpine and subalpine grassland vegetation in Middle Asia. A total of nine new associations and three communities were distinguished. New vegetation types at potential class rank for Irano-Turanian subalpine and alpine grasslands have been proposed: forb steppes with Eremogone griffithii and Nepeta podostachys in subalpine and alpine belts and alpine grasslands with Festuca alaica and Festuca kryloviana for mesic habitats in the alpine belt. The main factors differentiating the species composition were the mean diurnal temperature range, the sum of annual precipitation, precipitation seasonality and the minimum temperature of the coldest month. Conclusions: Our study sheds light on the open habitat vegetation in the Pamir-Alai Mountains and has contributed to the consistent hierarchical classification of the vegetation of the eastern Irano-Turanian region. Subalpine and alpine forb steppes are a very interesting and distinct grassland type in Middle Asia. The syntaxonomic position of some of the distinguished communities is still unclear and further research on this type of alpine and subalpine vegetation within the mountains of Middle Asia is needed. Taxonomic references: The nomenclature of the vascular plants follows Plants of the World Online (POWO 2023) and problematic taxonomic issues were solved according to The World Flora Online (WFO 2023). Nomenclature of Stipa spp. follows Nobis et al. (2020, 2022) and of Geranium spp. Cherepanov (1995). The nomenclature of bryophytes follows Ignatov et al. (2006). Abbreviations: DCA = Detrended Correspondence Analysis.