Characteristics Of The Phytocoenosis In Datong Country

This paper takes Qinghai Datong area as the research object, revolving around the mutual responds and relationships between the environmental gradient and vegetation characteristics, this paper carries on the research on the vegetation classification, the connection between community distribution and environmental factors, population niche, community diversity and community stability by investigating a large number of vegetation communities in this region and combining multivariate statistics such as TWINSPAN, DCCA, canonical correlation analysis and principal component analysis .The main conclusions this paper comes to are as follows:(1)DCCA ordination analysis shows that in Qinghai Datong area the distribution of plant communities under the mixed influence of orographical factor and water content demonstrates a high correlation with soil water content, and micro-topographigraphy, as illustrated in each axis of DCCA. Altitude, slope degree, direction and water content as micro topographical factors can produce a significant influence on the distribution of plant community.(2)The niche breadth of main vegetation can reflect the adaptability to the environment and evenness of distribution of populations. Galeopsis bifida,E. sinica,Picea crassifolia, P.rotundifolia ,Betwla platyphylla have higher niche width and stronger adaptability, hence becoming a dominant populations in this region; while C. crebra,P. viviparum, Lancea tibetica, G. Pylzowianum have lower niche. Not all populations with lower niche are dominant populations. This peculiarity depends on the range and evenness of distribution of the certain population. Populations with higher niche breadth always have higher niche overlap, but not all populations with smaller niche breadth have lower niche overlap.(1)"Species diversity"is proposed to comprehensively evaluate species compositing as well as the community effect of the related species. The result show that both on the sequence from cultivated farmland to converted land to natural forest and the sequence from the newly converted lands to long-term converted lands, the Shannon-Wiener diversity index and Gleason richness index shows a"small-big-small"process, while the Simpson dominance index and Hill evenness index present a contrary process. On the process of community succession, species diversity doesn't present a monotonously rise or drop trend. The result indicates that we should fully take the succession stage into consideration in the evaluation of species diversity. Neither it is reasonable to think that the communities with the highest species diversity are the best, nor is it advisable to imitate the climax communities with the least species, let alone judge the stability of the plant communities only by species diversity.(4)The stability of typical plant formations in Qinghai Datong area is analysed by using M. Godron methods, The result indicates: all the plant formations of Qinghai Datong are unstility in certain extent, Form. Betwla platyphylla, Form. Sabina przewalskii., Form. Hippophae, Form. Picea crassifolia. have a higher stability,Form. agricultural land have lower one.