Research On The Characteristics And Diversity Of Plant Community In Closing Watershed Of The Loess Area In Western Shanxi Province

This study was conducted in the characteristic closed small watershed - Liugou watershed the Loess Plateau of Western Shanxi. Based on sample line method and sample plot method, the relative important value, community a diversity index (Shannon-Weiner index,Pielou index,Simpson index), community similarity coefficient (Jaccard index), and evaluation method of community stability was used. The plant community of closed small watershed - Liugou watershed the Loess Plateau in 2007(closed small watershed for 26 years) and 1996(closed small watershed for 15 years), as well as grassland with just closed were employed to investigate so as to obtain the data on vegetation, soil etc. According to the comparison of experimental data, the dynamic characteristics of vegetation community in small watershed were analyzed including community composition, species diversity, community similarity, community stability, the biomass and so on. The results showed as followed:On the upper hillside and sunny slope, the dominant tree species of community was Robinia pseudoacacia, and the dominant herbaceous specie was Carex humilis, with 26 years closed. On shaded slope, the dominant arbor and shrub of community was Quercus liaotungensis. and the dominant herbaceous specie was Potentilla chinensis. On half shaded slope, the dominant arbor and shrub of community was Syringa pekinensis. and the dominant herbaceous specie was Potentilla chinensis. There were mostly dominated by Forsythia suspensa,Ostryopsis davidiana and Carex tristachya on gully erosion. Through the Jaccard coefficient of community similarity index analysis, it was further confirmed that there were similar species composition of the plant communities with similar environmental factors. Compared the different habitat types of community diversity, community stability were found that the plant communities were in a stage of a certain degree of instability, relative stability of habitat with the order of half sunny slope> upper hillside > gully bottom > half shaded slope> shaded slope> sunny slope.Compared to communities with 15 years closed, arbor and shrub layer of community with 26 years closed had significant changes in species composition, the proportion of Syringa pekinensis,Robinia pseudoacacia,Platycladus orientalis were marked increase, and play a more important position, and the proportion of Hippophae rhamnoides,Ostryopsis davidiana which were the main species in the early closed had declined markedly. Due to the different types of environmental habitats, there were found the difference exists among the variation of the vegetation community.With the vegetation restoration gradually, the Shannon-Weiner index and Pielou index of arbor and shrub layer were significantly increased, Simpson's index was declined, and community stability was improved. The results showed that vegetation community as a whole was developed in more rich, uniform and stable direction with the closing time.Compared to communities of grassland with just closed, arbor and shrub layer of community with 26 years closed had retained most species in the early closed community, especially in half shaded slope community. Herbaceous species were more rich and occupied the main position in the early closing, however, herbaceous species were diminishing with the closed time and the role was reduced continuously; in particular, a number of pioneer species such as Glycine soja, were gradually degraded or disappeared. Some species such as Pinus tabulaeformis which could adapt to change of environmental elements were gradual development and growth. Then Community structure was more complex, community composition was more uniform and reasonable.The changes of community biomass in closed watershed with different years showed that the biomass in different habitats was increased with the closed period.