Distributional patterns of seed plant diversity in wet and aridification habitats along an elevational gradient in an alpine meadow

Because of the influence of global change and external disturbances, habitats of alpine meadows are trending toward aridification in the Qinghai-Tibetan Plateau. How would variation in habitat affect the elevational pattern of species diversity? Nine sample plots were set along an elevational gradient in the Dongda Mountains in southeast Tibet. Ten 1 m×1 m sample quadrats were set in each sample plot, with five quadrats located in wet habitat and the others located in dry habitat. Species composition in each quadrat was investigated. Species with a frequency lower than seven were defined as occasional species; otherwise, the species were common. For total occasional and common species, variation of α, β, and γ diversity were respectively analyzed along the elevational gradient. β diversity was measured by the Cody index (βc), multiplicative partitioning (βw), and the slope of regression between similarity of species composition and distance (βslope). There were 160 seed plants recorded in these sample plots, among which, 132 species were distributed in wet habitats and 107 species in dry habitats. For total and occasional species, α and γ diversity both decreased with elevational gain in wet habitats but increased in dry habitats. For common species, α and γ diversity both presented an increasing trend with elevational gain in wet and dry habitats. The elevational patterns of β indexes were not consistent,βc and βw in wet habitats were higher than that in dry habitats, and βc and βw of occasional species was higher than that of common species. The elevational patterns of species diversity between wet and dry habitats were different, and diversity of occasional species had a high value, and will directly affect elevational patterns of species diversity.