Study On The Vertical Pattern Of The Plant Communities In Youshui Basin, Qinling Mountains

Qinling Mountains are the main natural boundaries of north-south climate, vegetation types and typical regions of vegetation transition zone. So the study of plant community characteristics, bio-diversity is valuable, and has been paid much attention by many ecologists. The Youshui basin was chosen as the study area, using typical sampling and systematic sampling techniques, we systematically analyzed the different structure and composition of community in different site conditions according to different role of environmental factors, the numerical classification of the plant communites, and get the variation rules of the community structure and plant diversity along the altitudinal gradient. The result was shown as follows:The vegetation survey on the natural communities in the Youshui basin, Qinling Mountains indicated that there were 460 species of vascular plants in 238 genera of 105 families,including101 families of Angiosperm, 1 family of Gymnospermae and 3 families of Pteridophyta in the research area. Rosaceae and Compositae are the biggest families, which contains 62 and 26 species, respectively. The results also show that the vertical structure of the community was obvious, which was composed of tree layer, sub-tree layer, bush layer and grass layer, but there are less interstratum plants. The diameter level of trees in broadleaf forest communities showed a "J" type, but the coniferous forest communities showed an stable diameter level.Using two-way clustering analysis, the plant communities in Youshuihe basin was divided into 33 types. The 52 plots were analyzed by DCA, and the results indicated that the first axis of DCA from left to right showed the changing value of environmental gradient with the elevation increasing gradually; and the second axis of DCA from bottom to top showed an integrated environmental gradients—an increasing trend of humidity, soil thickness and runoff. Because of the big span of latitude and longitude and the complexity of environmental factors variation of Qinling Mountain, and there are some local niche changes in different regions, so the complexity of the distribution pattern of plant diversity was reflected. DCA ordination can well reflect the relationship between the diversity of plant and the environmental factors, the climate variables and habitat heterogeneity. In order to explain the environment factors better, DCCA was adopted to analyze the ecological relationship of plant communities. DCCA biplot can well reflect the habitat status of every community, in soil of the communities habitat.Elevation increased gradually along the first DCCA axis from right to left. Basically, the second DCCA axis showed the change trends of humus thickness of the site soil, habitat moisture and soil texture. The physicochemical properties of the soil and habitat moisture become better, and there was a trend that the aspect changed from sunny slope into shady slope. Comparing the results of DCA with DCCA ordination, we found that they inosculated with each other. DCA ordination reflected more information about the species, while DCCA reflected more information about the environmental factors. However, the relations and relative position of all the plots had not changed, and all 35 formations had relatively clear boundaries, which proved the results of two-way clustering was fully correct.Analysis of community diversity of natural forests in QinLingYou Basin shows that the species diversity was the highest in 2000m. The richness index and the Shannon-Wiener index was the highest among 1700m-2000m, but the Pielou evenness index did not show any obvious rules.