Response of species diversity in Caragana Korshinskii communities to climate factors and grazing disturbance in Shanxi, Shaanxi, Ningxia and Inner Mongolia
晋、陕、宁、蒙柠条锦鸡儿群落物种多样性对放牧干扰和气象因子的响应

Caragana korshinskii is a leguminous perennial deciduous shrub species commonly found in arid, semi-arid lands in the loess plateau in northwestern China. This speices maintained the vigorous capacity of reproduction, regeneration and drought-resistance, good for soil conservation against wind-erosion and desertification. C. korshinskii is also an excellent forage and medicinal plant with high economic values and industrial usage. This study examined indices of richness, diversity and evenness to study the response of species diversity in C. korshinskii communities to climate factors and grazing disturbance in Shanxi, Shaanxi, Ningxia and Inner Mongolia. The results showed that: (1) The species composition of community were found simple and less diversified. There were 111 angiosperm speices in 64 genera of 25 families, C. korshinskii were dominant species of scrub layer; and main species of herb layer included Compositae, Leguminosae, Chenopodiaceae and Gramineae. All of them were annual, xerophyte and super xerophytic plants, which showed drought resistance of C. korshinskii communities. In the scrub layer of forest steppe, there were many other species coexisting with C. korshinskii. Comparing with forest steppe and typical steppe, Chenopodiaceae species were more commonly in desert steppe; (2) In response to anthropogenic activities, as well as soil and climate factors, the Patrick index, Simpson index and Shannon-Wiener index all fluctuated at large scale, but along the similar trend. Generally, richness index and diversity index in Shanxi and Shaanxi were higher than in Ningxia and Inner Mongolia, while the Pielou index remained stable; And (3) according to the distance between samples of C. korshinskii communities and residence, grazing intensity were divided into 4 grades,including D4, D3, D2 and D1 as the order from strong to the weak. Grazing intensity was found significantly correlated to Simpson index(P<0.01) and Shannon-Wiener or Patrick index and Pielou index(P<0.05). The species richness in the communities gradually decreased with the aggravating of grazing intensity. The indices of species diversity index and evenness peaked at D2 and D3, suggesting that moderate disturbance would enhance biodiversity and evenness; (4) Significant positive correlations were observed in Patrick index, Simpson index and Shannon-Wiener index to annual precipitation(P<0.01)and annual relative humidity(P<0.05). Fluctuations of annual precipitation and annual relative humidity along the similar trend, showing the dominant role of water content in determining the plant diversity in C. korshinskii communities. Annual precipitation was more than 400 mm in Shanxi and Shaanxi, richness index and diversity index of communities were high, and perennial plants were in the ascendant. However, in Inner Mongolia, annual precipitation was lower and rainfall focused on July and August, causing richness index and diversity index declined and annual plants were common