[ Objective] The aim was to study the distribution of vegetation and its relationship with environmental factors in Yellow River estuarine wetland. [ Method] According to the data of the plant sample investigation and the related environmental factors in Yellow River Delta National Na- ture Reserve in 2009 -2010, the plant community changes and its relationship with environmental factors in temperate estuary wetland were ana- lyzed. [Result] There was little vegetation in the Yellow River delta and the distribution of plant was influenced by environment. Judging from the vegetation structure, the vertical structure of vegetation in the supralittoral zone zone vegetation cover included arbor layer, shrub layer and grass layer. The importance of grass was larger than shrub and arbor. In the intertidal zone, the vertical structure of plants was divided into shrub and herb layers. Judging from the variety, the species in the supralittoral zone was higher than that in the intertidal. The first principal component elected by Principal Component Analysis better reflects the salt of the study area, and the second principal component better reflects nutrient information. Regression analysis showed a positive correlation between importance value and the total salt content and electrical conductivity. In other words, if the total salt content and electrical conductivity increases, the importance value rose. However, the diversity index decreased as the total salt con- tent and electrical conductivity increased. [ Conclusion] The study provided theoretical basis for the ecological protection of vegetations and formula- tion of regional policies.
KOU Ming-juanLIU Jia-zhenCHEN Yong-jinZHU Hai-yongLU Ya-kunLU Ming
To investigate climate evolution during the Miocene, especially during the Middle Mio- cene climate transition on the northeastern Tibetan Plateau, stable oxygen and carbon isotopes of car- bonates from a 288-m-thick lacustrine-fluvial sediment sequence covering the period from 17.1 to 6.1 Ma from Tianshui Basin, China, were analyzed. The relatively low stable oxygen isotope values indicate the prevalence of wet climate conditions during the period of 17.1-13.6 Ma, an interval corresponding to the well-known Middle Miocene Climate Optimum. The interval between 13.6 and 11.0 Ma （i.e., the late Middle Miocene） is marked by a progressive increase in the δ18O values, indicative of a decrease in precipitation, probably linked to the expansion of the East Antarctic Ice Sheet and global cooling since about 14 Ma. The climate in the study area continued to get drier as shown by the enrichment of the heavy oxygen isotope from 11 Ma. We attribute these stepwise climatic changes as revealed by our car- bonate δ18Orecord from the northeastern Tibetan Plateau to the sustained global cooling that may have reduced moist transport to Central Asia, which in turn led to a permanent aridification.
