Study On Community Structure Characteristics Of Yunwu Mountain

Grassland resources were destroyed and its ecosystem deteriorated seriously because of harsh natural conditions and increasing of humans activitives, which finally can cause habitat loss and species diversity decreased. Yunwu Mountain nature reserve is the unique typical steppe nature reserve in Loess Plateau, and has been had unique and complete grassland ecological landscapes. According to the systematic investigation on enclosure and grazing grassland, this paper analyses the process in temporal and spatial changes of the community structure characteristics and species diversity on Yunwu Mountain. The results show that:1. The dominant species and accompanying species were not all the same in different grassland types (enclosure and grazing) and different succession stages of same grassland type (Stipa bungeana and Thymus mongolicus), and the dominant species changed in different month following the plant growth period. The CCA ordination for species-environment factors in different months indicated that the first two axes can clearly explained the relationship between species-environment, but can't explained the species distribution well. Multiple comparison and frequency analysis were performed to analysis the biological characteristics, and the results showed the advantage of enclosure grassland in different angle.2. Based on the research of the growth pattern of major dominant species in the communities, the growth of the plants is basically coincident with Logistic models before the height and individual aboveground biomass reaches to the maximum, and there is a dynamic fractal relationship between them. The function as follows:lnB=D*lnH+lnC; In this experiment both plant height and plant individual aboveground biomass have a significantly logarithm correlation with precipitation accumulation as the function of y=a*lnx+b.3. Based on the research of grassland community diversity, the fluctuate trend of all species diversity index were similarly in community. The correlation analysis showed that except no significant correlation was found between evenness index and Margalef index in enclosure grassland, significantly or very significantly correlated were found among all other index in each community. Simpson,Shannon-wiener diversity index and Margalef's richness indexes in the enclosure grassland (S. bungeana Community and T. mongolicus community) and evenness index in grazing grassland were significantly or very significantly parabola relationship with the biomass. Comparing with S?qrenson similarity index, Bray-curtis index was more concrete, and can explain the continuity and progressiveness of species composition structure during the succession process.