The Distributing Characters Of Plant Species And Plant Community Diversity In The Water-level-fluctuating Zone Of Three Gorges Reservoir

Water-level-fluctuating zone (WLFZ) is a transition ecological environment between terrestrial and aquatic ecosystems. In Three Gorges Reservoir Region (TGR), with the attractive characters of environmental factor, ecological processing and gradients of plant communities, WLFZ becomes the key system for controlling terrestrial and aquatic ecosystems. It is very important to keep the WLFZ ecological functions run smoothly after TGR operation, such as riverbank stabilization, soil conservation and creation of beautiful landscape, which will be very helpful to recover the WLFZ after the impoundment of Three Gorges Dam. For this purpose, we need to investigate the distribution and diversity of present plant communities, to confirm the dominant plant communities in this area, and to get the information for their living environment. With all these informaton, we can build a stable, varied plants database, which is the foundation for make the scientific strategy to recover the WLFZ after the TGR operation.From2009-2010, the project,'Research Work for Main Wetland Creatures Resource in Chongqing', was investigated in Three TGR in9counties, Wushan, Fengjie, Fengdu, Zhongxian, Yunyang, Kaixian, Shizhu, Fulin, and Jiangjin. We investigated all the wild plants in WLFZ of the9counties. With setting typical plots and line-transit, all the plants information, such as plant name, their living characters, and their varied characters were recorded. For those we can't identify in local area, we took the pictures, brought the plant samples back to lab to identify.To investigate the dominant plant communities in WLFZ in Wushan, Fengjie, Yunyang, Kaixian, Zhongxian, Fengdu,180plots were set depending on different water flood. We recorded all the information including plants'number, height, coverage, and their micro-living environment. We investigated the floristic composition, spatial distribution pattern, community classification, ordination and species diversity in these plots. Statistical software were performed to analysis data. The key conclusions of the study are as follows.(1) Based on field survey, in WLFZ of Three Gorges Reservoir Region (TGR) in Chongqing, there were466kinds of seed plants, which belong to78families,253genera. Among them, there were2species of gymnosperm, belong to1families,2genera. Herbaceous plant had an absolute predominance in WLFZ in TGR of Chongqing. In herbaceous plants, Compositae, Gramineae and Cyperaceae were the main families. In terms of genus, large genus was rarity, but single genera and specy was excessive. The geographical distribution and composition of flora in WLFZ was very complicated. The geographical composition of this area had many types, such as, tropic, temperate, Eastern Asian and Mediterranean. In geographical distribution, the disjunction distribution took a large proportion. With all the plants information we got from field survey, we built our database, Directory of Vascular Plants in Water-level-fluctuating zone of Three Gorges Reservoir in Chongqing (Appendix1). Directory of70Dominant Species in Water-level-fluctuating zone of Three Gorges Reservoir in Chongqing (Appendix2).(2) Based on the TWFNSPAN classification,50plots were divided into15associations, be classified as three types. The distributions of aquatic plant communities were consistent with the water in the environment which basically represented the major plant communities in water-level-fluctuating zone in the TGR in Chongqing. There were four wetland plants in these communities, submerged aquatic vegetation, emergent aquatic plants, and fixation of both floating-leaved aquatic plants and submerged, emergent aquatic plant. Aquatic plants communities can also be classified as three types, submerged plant community, fixed floating leaves community and emergent plant community. Emergent plant was the major community.We also analyzed the plants in WLFZ by Detrended Correspondence Analysis (DCA) compositor, the feature values of the first and second ordination axis were0.884and0.718, respectively. According the results, the distributions of aquatic plant communities were consistent with the water in the environment. The first ordination axis reflected basically the effects of water on aquatic plants which increased gradually from left side to right side. The second ordination axis reflected the close relationship of soil moisture and the life form of dominant aquatic plant species. The DCA compositor data showed that the main species had the same location on the species map and the community compositor ranks, which means the distribution of aquatic plant communities was closely related to the spatial distribution of dominant species. The ecological environment type and the gradient, which were reflected by the first and second ordination axis values, were corresponding with the DCA compositor data. These results were showed that the spatial distribution of plant species was very similar to the distribution of the communities.(3) We used7indexes to evaluate the spatial distribution pattern of dominant plant species, diffusion index (ID), aggregation index (ICS), green index (GI), aggregation frequency index (ICF), mean crowding index(IMC), poly-block index (IP) and Maurice west index (IM). The results showed that,1) the distribution of all dominant species had different aggregation intensity, the lower threaten of fluctuating water flood, the lower dominance of dominant species.2) The spatial distribution pattern of plant species was affected by fluctuating water flood, but which is not the only reason.3) In different section, same plant species had the different aggregation intensity, which mainly related to the local environments. In same section, different plant species had different aggregation intensity, which related to their breeding habits.4) In each altitude section, Cynodon dactylon community was the dominant species, because of its tolerant ability to flood, drought, and soil leanness, and with abundant root mass, nutritional reproduction method. The distribution pattern of other species was not obvious.(4) The analysis of a-diversity in plant communities showed that species diversity mainly affected by flood seasonal in WLFZ in the TGR. With lower elevation, longer and deeper flood, there were greater flood disturbance to the species diversity, which showed a downward trends significantly. Comparisons of various indices of species diversity, the results were concerted among species richness, Simpson diversity index and Shannon-Wiener information index, but the species evenness index was had little difference. To analysis species evenness, Pielou evenness index and Alatalo index stayed the same. Otherwise, to analysis the plots with less species, Pielou index was much better than Alatalo index. The results in good agreement between Simpson diversity index (SDI) and Shannon-Wiener information index (SWI) analysis. SWI was more sensitive than SDI to species diversity analysis, but SDI was more stable than SWI because of the species evenness. Species diversity index which based on the number of individuals and the important value of species stayed consistent in practice, but it was better to use species diversity index which based on the important value of species. Whereas, for species richness analysis, it was better to use species diversity index which based on the number of individuals.(5) The analysis of (3-diversity for plant species of WLFZ in TGR showed that the number of plant species and overall number of plants increased with the altitude elevation, the flood threaten decrease, and other changes in living environments, and accompanied by increased plant species diversity, decreased species similarity, and species alternation.The plant species distribution in WLFZ can be influenced strongly by fluctuating water flood. The more fluctuation flood, the less plant species. The ecological environments in TGR can be affected by many factors, including cyclically water-level changing, soil and its nutrition running off, environmental pollution, and large facilities construction. Further, the plant diversity and ecological safety can be threatened by those consequences. In order to recover the plant cover and to protect the plant species diversity in WLFZ in TGR, we need to keep doing the scientific research work on the effects of flood water on the ecological environment and plant living. We also need to investigate the plant resources and wild plants in this area, especially the rare, unique and key wild plant species, to take corresponding countermeasures on protecting the plant resources in WLFZ in TGR.