Studies On The Species Diversity In Vegetation Succession In Ziwuling Area

The component structure, floristic characteristics, species diversity, community productivity, soil physical-chemical properties, and the relationship between species diversity, community productivity and soil factors was tudied in vegetation succession in Ziwuling area on the Loess Plateau. The results are as followed:1. There are 114 species in 87 genera and 40 families including 10 species of trees, 29 species of shrubs, 71 species of herbs and another 4 species of liana in vegetation successional in Ziwuling area. As to the plant floristic composition, the 40 families belong to 6 geographical elements and the 87 genera belong to 9 geographical elements in vegetation succession. Both the family and genera with temperate distribution are dominant in this area. The analysis of life form spectrum of flora shows that the phaenerophyte and phaenerophyte are the dominant life form which account for 42.1% and 40.1% respectively, followed the geocryptophytes with 12.3%. The chamaephytes and therophyte less distributed in the area that is no more than 5%.2. The species diversity increased with vegetation succession. From the initial stage to the end, the Margalef index increased by 196%, Shannon-wiener index increased by 149% and Simpson index increased by 218 percent. With community succession, the Sorensen index and Jaccard index had a decrease of 66.1% and 70.3%, while the Cody index gradually increased by 150%. The layeredαdiversity indicated that the species diversity index of herbs in the initial stages were larger than latter, the species diversity index of shrubs increased with succession and the increased range were greater in early stage, furthermore, all other species diversity indexes of trees in climax community were bigger than in Pioneer arbor community stage except Simpson index.3. With the succession, soil organic matter and total nitrogen showed an upward trend, soil available nitrogen and soil moisture were fluctuating, and soil bulk density decreased slightly. The soil organic matter, total nitrogen, available nitrogen and soil moisture of 0 ~ 20 cm layer significantly rise with the succession. The soil organic matter and total nitrogen of 20 ~ 40 cm and 40 ~ 60 cm layer declined markedly and soil moisture and soil bulk had little increase compared to 0 ~ 20 cm layer. The soil available nitrogen had greater fluctuation in different succession stage. 4. The community species diversity and surface soil environmental factors have closely relationship that gradually weakened with the soil depth in the succession process. The soil organic matter and total nitrogen are significant or very significant positive correlation with species diversity, then soil moisture and soil available nitrogen, the correlation between soil bulk density and species diversity are the weakest. The 20 ~ 40cm layer of soil organic matter and soil total nitrogen showed weak correlation with community species diversity and the 40 ~ 60 cm layer of soil environmental factors showed no correlation with community species diversity.