Patterns of plant diversity change across arid landscapes of the Aral Sea region (Central Asia)

Arid and semi-arid ecosystems of Central Asia are undergoing rapid transformation due to climate change, large-scale anthropogenic pressure, and desertification processes, particularly following the desiccation of the Aral Sea. The vegetation cover of the Aral Sea region (Uzbekistan) represents a unique natural laboratory for studying long-term changes in biodiversity and community structure under increasing aridity and environmental stress. This study aims to assess temporal and spatial changes in plant biodiversity in the Aral Sea region by comparing historical and contemporary geobotanical data, with a focus on α- and β-diversity patterns across major vegetation types and landscape units. We analysed historical vegetation records (1960s–1990s) and contemporary field data collected during expeditions in 2020–2023 across five natural–geographical regions (Ustyurt Plateau, Eastern Chink, dried Aral Sea bed, North-Western Kyzylkum, Amu Darya Delta) and five vegetation complexes (halophytic, gypsophytic, psammophytic, tugai, and takyr communities). Alpha diversity was quantified using species richness, Shannon diversity index, and dominance index, while beta diversity was assessed using Whittaker’s approach and SDR simplex decomposition (similarity, species replacement, and richness difference). Multivariate analyses (NMDS), kernel density estimation, and generalized linear models were applied using R software. Comparative analysis revealed pronounced shifts in vegetation structure and biodiversity over time. Most vegetation types exhibited a decline in species richness and Shannon diversity, accompanied by increased dominance of a limited number of stress-tolerant species. Halophytic and gypsophytic communities showed substantial losses of species richness in the dried Aral Sea bed and North-Western Kyzylkum, whereas psammophytic communities demonstrated partial recovery in some areas. Beta-diversity patterns indicated that species loss dominated in highly degraded regions, while species turnover prevailed in relatively stable landscapes such as the Amu Darya Delta and parts of the Ustyurt Plateau. The observed changes reflect ongoing desertification, climate-driven aridisation, and anthropogenic pressure across the Aral Sea region. Spatial heterogeneity in α- and β-diversity responses highlights differing ecosystem resilience among vegetation types. These findings underscore the importance of long-term biodiversity monitoring and provide a scientific basis for conservation and restoration strategies in arid landscapes of Central Asia.

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