Study On The Ecological Characteristics Of Caragana Communities In Shanxi, Shaanxi, Ningxia And Inner Mongolia

The Genus Caragana (Leguminosae:Fabales) contains the deciduous shrub species with the distribution in temperate regions of Asian and the Qinghai-Tibet plateau. In China they are mostly found in arid or semi-arid areas in the north of Yellow River, the Qinghai-Tibet plateau at Southwestern and Northwestern Region, with a few species in the lower reach of Yangtze River in Southern part of the country. The species in Caragana are good for soil conservation and wind-erosion prevention as desert shield, as well as of high economic values for industrial use. This thesis employed quantitative methods to examine the ecological chrematistics of Caragana in the provinces of Shanxi, Shaanxi and Ningxia and the Inner Mongolia Autonomous Region, including the classification, ordination, interspecific relationships of dominant species, and the species diversity of Caragana communities. The purpose is to provide the basic data on the community ecology of the genus, fundamental to the utilization of the plant resources and to vegetation reclamation in mid-and northwest China where suffers severe land degradation.The Caragana communities were sampled from 58 quadrates and the analysis was made using TWINSPAN, DCA and DCCA with the results as follows. The TWINSPAN analysis classified Caragana communities into 11 types. The DCA ordination was found well fitting the relationship among the communities and their environment, as shown by the distinct distribution boundary of each community in DCA ordination plots. The total 11 communities were divided into 3 Groups namely A, B and C based on the dominant species. Group A contained all the quadrates ofⅢ,Ⅳ,Ⅴ,Ⅵ,Ⅸ, communities with Caragana korshinskii as dominant species at scrub layer. This group covered the Loess Plateau and steppe- or common deserts western Inner Mongolia. Group B contained 16 quadrates of I, II, VIII, X communities with C. ntermedia as the dominant species at scrub layer. It covered steppe desert zone and the sandy land at northern part of the Loess Plateau. The Group C contains 3 quadrates of XI community with C. microphylla as dominant species at scrub layer, founded at the meadow steppe and the common steppes in eastern Inner Mongolia. The DCCA ordination plots showed quadrates of sufficient concentration, well revealing the relationships of the samples to the environment.The interspecific association and correlation among the dominant species in Caragana communities were studied usingχ2-test, Jaccard association index, Pearson correlation coefficient and Spearman rank correlation coefficient. Only a few significant, mostly negative, correlations were identified among the species pairs. This suggests that the Caragana communities are under dynamic succession, prone to fluctuation by external disturbance or even degradation. The interspecific association and correlation analysis classified 20 dominant species into 3 ecological groups, i.e. C. korshinskii group, C. ntermedia group and C. microphylla group. The species with a group all showed relatively positive associations indicating the inter-dependent relationships with similar resource utilization and ecological demands. In contrast, the associations between the groups were loose and scattered showing distinct regional differentiation.This thesis also used indices of richness, diversity and evenness to study the response of species diversity in Caragana communities to climate factors and grazing disturbance. In response to anthropogenic activities and the soil and climate factors, although the Patrick index, Simpson index and Shannon-wiener index all fluctuated at relatively large scale, the general trend was similar, and the Pielou index remained stable. 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 grazing intensity. The indices of species diversity index and evenness peaked at D2 and D3, suggesting that moderate disturbance would enhance biodiversity and evenness. 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), showing the dominant role of water content in determining the plant diversity in Caragana communities.