Study On Quantitative Ecology Of Elaeagnus Mollis Communities In Shanxi

Elaeagnus mollis is one of the larger shrubs and dwarf trees, being an endemic to China and one of the state-protected two-grade rare and threatened plants, In China, Elaeagnus mollis is only distributed in both Shanxi and Shaanxi, especially distributed mostly the south of Luliang Mountains and the midst and west of Zhongtiao Mountains, Shanxi. The community composed of Elaeagnus mollis as the constructive species is one of the typical vegetation types in the hills and lower-mountains of southern of Shanxi.The ecological relationship of species, community and environment in Elaeagnus mollis communities were studied by using TWINSPAN and DCA. The results of TWINSPAN indicated that the communities were classified into 10 Associations, and the quadrats classification indicated two environmental gradients which were light intensity and soil humidity. The results of DCA suggested the first axis showed light gradients and the second axis reflected humidity gradients.The nearest neighbors of each individual and the distances between each individual-neighbor pair in Elaeagnus mollis communities were obtained by using the nearest neighbor's analysis. Based on the primary results above, the spatial pattern and interspecific segregation in the communities were studied by X2 test with a subtable method of a N×N nearest-neighbor contingency table. The result showed that the segregation relations for most of the species-paires are random (80.94%), some species-pairs are positively segregated (18.78%), and fewer species-pairs are negatively segregated (0.28%). Negative segregation may occur between dwarf shrubs with similar habitat requirements. Intensive interspecific competition may result in random or even uniform distribution, therefore, such species-pairs are apt to be negatively segregated. Large individuals tend to be positive segregated with the other large arbors since their size prevents them from occupying a small habitat.Stand structural diversity is useful in forecasting individual growth and can be indicative of overall biodiversity. Many variables related to structural diversity can be measured. However, species, diameter, and height are commonly measured and indicate changes in vertical and horizontal stand structure. The structural diversity of Elaeagnus mollis communities was studied by using both extended Shannon-Weaver index and STVI (structure index based on variance). The result from the both indices showed similar change tends. Moreover, there was smaller difference for the structural diversity value among all of plots. Elevation is not a main factor affecting those indices. The structural diversity indices of all kinds of the community indicated that the community types, the other environmental factors, and human activity are main factors effecting structure diversity.