Grassland composition, structure, and diversity patterns along major environmental gradients in the Central Tien Shan

摘要

What species and traits signal vegetation types along prominent environmental gradients in the Central Tien Shan and what are the corresponding diversity patterns? Vegetation was sampled at 41 sites throughout the Kyrgyz Republic using quadrats stratified throughout a 1,000-m(2) sample area. Relationships among major environmental gradients, vegetation structure, and species composition were explored with nonmetric multidimensional scaling. Species distributions were examined to characterize phytogeographic patterns. Seven vegetation types ranging from desert grassland to meadow steppe were identified with cluster analysis, ordered primarily along elevation/mean annual temperature gradients. Four arid grassland types were distinguished, ranging mainly from 900 to 1,700 m elevation, and characterized by co-dominance of grasses and forbs with secondary dominance by shrubs. Annual and biennial forbs equaled perennial forbs in total importance. Grasses include C3 and C4 species. Three montane grassland types were recognized and characterized by co-dominance of perennial C3 grasses and forbs. Transition to montane steppe occurred from 1,500 to 1,900 m and is correlated with absence of C4 grasses and dominance of Festuca valesiaca. Highest diversity was found at intermediate elevations, from 1,800 to 2,600 m, in meadow steppe habitats. Forty-six percent of 580 identified species are Middle Asian endemics and remaining species primarily have distributions including Eastern Europe, the Caucasus, and western Siberia. Although grassland degradation from overgrazing has been chronic throughout the region, grasslands are widespread throughout the Kyrgyz Republic and many, particularly mid-elevation meadow steppes, retain high levels of native species diversity.