| The littoral zone (riparian zones, etc.) is an important component of wetlands and is the ecotone between terrestrial ecosystem and aquatic ecosystem, which has the characters of materials and energy frequently exchange, extremely rich biodiversity and so on. Vegetation of littoral zone is an integral part in wetland ecosystem, which has a significant impact on ecological processes of transport and transformation of material, energy cycles, as well as distribution pattern of biological community. Study on the characteristics of vegetation of littoral zone not only helps to understand the evoloution of wetland, but also to enhance the wetland ecosystem and has important significant on biodiversity conservation.In this paper, Baijia Stream of Pengxi River of Kaixian County is the the place of research. Base on system analysis of hydrology of Three Gorges Reservoir, water level fluctuationis is the main line. The soil seed banks of littoral zone are studied by germination test and field investigation. Then from the perspective of competition between plants, competition intensity and competition results of dominant species are studied to prediction the evolution of vegetation. Finally, plant flora, community type,αdiversity of community and distribution pattern of biomass of littoral zone are analyzed through systematic sampling of communities investigation.The results of the thesis are articulated as below:(1) The soil seed banks are studied by the methods of germination test and field investigation. The effects of water level fluctuation on the distribution pattern of soil seed bank is significant. The ground vegetation species richness, species richness of soil seed bank and seed density show a decreasing trend with the increasing of flooding intensity.(2) The intra-and interspecific competition of dominant plant are studied. Due to the competitions of plants, the quantity of plants have significant change between early and growth stage of growing season. Plant competition intensity decreases gradually with distance (P<0.01). When the distance between plants is under 30 cm, the competition is fierce and interspecific competition is stronger than intraspecific competition. Furthermore, the fiercest competition happens between plants with a distance under 10 cm. Individual quantity and height of dominant species increase with distance between plants, while the biomass, seed yield and branches decrease firstly and then increase. Species with high fertility and growth rate had advantage in competition, which ensure their survival in littoral zone.(3) The plants floral of littoral zone of Baijia Stream is analyzed. There are 34 families of vascular plants including 70 genera and 85 species. The rate of single-species families and the monotypic genera is high, the dominate plants are herbs. Comparing with 156 m hydrological cycle, the number of species is decreased. The floristic elements of the 30 families are composed of 4 area-types and 1 subtype, while there are 9 area-types of genus, the 66 genera are composed of 9 area-types and 4 subtypes. The Widespread and Pantropic are the majority geographic element of family and genera, which show that the plants of littoral zone are strongly disturbed by water level fluctuation. Species with high ecological amplitude and competitive ability ensure their survival in littoral zone.(4) The relationship between water level fluctuation and vegetation community is discussed. The vegetations are divided into 18 community types by TWINSPAN classification. Ass. Cynodon dactylon and the other 4 community types are the main types in littoral zone of Baijia Stream. With increasing of elevation, the Shannon index, evenness index, richness and patterns of biomass show distribution of"∧"type, while the Simpson index shows a distribution of"∨"type. Comparing with the hydrological cycle of 156 m,the community type andαdiversity change along with water level fluctuation.
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