Species diversity of grassland communities in the Aletai region of the northern Xinj iang province

A survey along a natural gradient at large scales was employed to investigate the variability of species richness and evenness of grassland communities growing in the Aletai region of the northern Xinjiang,and was completed in 1996~1997 and 2001 to address the relationship between elevation and biodiversity in this study.99 plots with the size of 1 m×1 m were positionted and sampled to collect data of plant communities at a vertical interval of 200 m between 1 000 and 3 100 m above sea level.The species diversity of plant communities was measured by using ShannonWiener (H) index,Pielou index (J),and species number (S).The results showed that richness index,evenness index and diversity index were significantly different among grassland communities.The study detected that richness index decreased gradually in the order of mountain steppe,mountain meadow,desert steppe,meadow steppe,desert,alpine meadow,mountain desert.Evenness index decreased gradually in the order of mountain meadow,meadow steppe,desert steppe,desert,alpine meadow,mountain steppe,mountain desert.Species diversity decreased in the order of mountain steppe,meadow steppe,desert steppe,mountain meadow,desert,alpine meadow,to mountain desert.Species diversity index was influenced by richness index and evenness index in a certain community,and evenness index contributed more to species diversity index than richness index did in a community distributing in the Aletai region of the northern Xinjiang.Species diversity increased with the increase of elevation from 1 000 m to 2 000 m,but decreased from 2 000 m to 3 000m.With altitudinal increase,the variational trend of diversity index was accordant with evenness index and richness index.