Abstract: After flooding to 156 m height, a wide area of wetlands emerged in the water level fluctuation zone of Three Gorges Reservoir. From July to September 2008, an investigation was made on the plant communities beside Baijia stream, the first order tributary of Pengxi River in Kaixian County of Chongqing. There were 33 species of wetland vascular plants, among which,  Paspalum paspaloides, Typha latifolia, Scirpus juncoides, S. triqueter, Polygonum longisetum were the dominant. The plant communities in study area were divided into eight associations. An obvious zonal distribution was observed at the lateral side of Baijia stream from riparian to 156 m altitude. There were three plant zones,  i.e., floodplain annual herb zone,  X. sibiricum zone, and P. paspaloides zone. With increasing elevation, the aboveground biomass showed a singlepeak pattern. During the period with lower water level, the increase of soil water content accelerated the growth of wetland plants. P. paspaloides was most dominant in the low lying area of second terraces of Baijia stream, and X. sibiricum widely distributed on the sloping field between the first and second terraces of the stream. The variations of soil water content and microgeomorphic pattern significantly affected the distribution of plant communities in water level fluctuation zone.

Key words: High altitude, Coppice tree, Disturbance, Analytic trees, Youth broken-down