Research On Species Diversity And Community Stability Of Minqin Liangucheng Nature Reserve

Based on theories of population dynamics and species diversity-community stability, we had studied community stability and species diversity of the five special communities in Minqin Liangucheng Natural Reserve in Gansu. The results showed that it was more comprehensive to evaluate community stability and species diversity from species diversity of shrubbery, reproductive strategy , population dynamics of dominant trees and primary productivity of shrubbery than from single factor. The important layers of communities were shrubbery, the proportion of shrubberies quantity were over 90%. The important values of shrubberies dominant trees were very higher than that of the sub-dominant trees, which showed that the dominating trees had obvious role in keeping community's structure and ecological function. The distributive patterns of the dominant trees were decided by species' biological characteristic and environments, the distributive pattern of Ephedra przewalskii and Potaninia mongolica were clump, and other species' were poisson. The dominant trees mainly breed offspring through Vegetative Reproduction, and Sexual Reproduction of many species had decreasing or ended, that benefited for species adapting to the stress environment and not benefited for evolution and scattering of species. The species diversities were decided mainly by distributive pattern of precipitation and variety of soil. It had obvious relationship between community stability and species diversity of shrubbery, the higher the index of shrubbery species diversity was, the more stabile the community was. It had immediate relationship between the stability of dominant tree and the stability of community, the more stabile the dominant tree was, the more stabile the community was. It had determinate relationship between the primary productivity of shrubbery and diversity of shrubbery, the higher the diversity was, the higher productivity of shrubbery was. Shrubbery had important role in keeping community stability, its index of species diversity had little variance, the more rich the species composition was, the more stabile the community was. perennial herbs and annual herbs only influenced the species diversity and physiognomic characteristic of community, but it had higher annual undulation and was not so important in keeping community stability. The dominant trees had been multiplying offspring through Vegetation Reproduction, and its Sexual Reproduction was weakened or ended, that was benefit for species to adapt stress environment and to promote population growth, but made against adaptability evolution and dispersal for far distance. There were lower index of species diversity in five special communities, the order from high to low was Oxytropis bicolor community> Potaninia mongolica community > Reamuria soongorica community> Ephedra Przewalskii community> Kalidium cuspidatum community, and the index order of shrubbery from high tolow was same as communities, but all of the five communities had higher index of ecological dominant because the dominant trees pad a important role in keeping community stability. The five communities had lower the primary productivity that contributed to shrubbery than herbage, the order from high to low was Reamuria soongorica community> Oxytropis bicolor community> Potaninia mongolica. community > Ephedra Przewalskii community> Kalidium cuspidatum community. The Oxytropis bicolor community had higher index of species diversity and lower index of ecological dominant than other community, Oxytropis bicolor and Caragana opulens, its preponderant trees are unceasing population, and Reamuria soongorica is declining population, on all account, the Oxytropis bicolor community is more stabile than other communities. The species diversity index of the Potaninia mongolica community was higher than that of three other communities and lower than that of Oxytropis bicolor community, and Potaninia mongolica, its dominant tree was stabile, therefore the community was a stabile community. The Ephedra Przewalskii community had lower index of species diversity and higher index ecological dominance than other communities and had great role in keeping the structure of community and species diversity, Ephedra Przewalskii was more stable, so that the Ephedra Przewalskii community was more stable. The Kalidium cuspidatum community was not stable and it preponderant tree was declining because of the lower index of species diversity and higher index ecological dominance. Despite its higher index of species diversity, the Reamuria soongorica community was not extremely stable because it had lost its ability of multiplying and resuming, it would be replaced by the community composted of herbages.