| Water-level-fluctuation zone (WLFZ) is a special area that flooded land periodically above the water since the seasonal water level fluctuating of rivers, lakes and reservoirs. With the accomplish of three-gorges reservoir, the mainstream and its tributaries of reservoir formed WLFZ with a vertical throw about 30m and an area about 300km2, which brought serious environmental problems. Pengxi river basin is the second largest tributary in Chongqing of the Yangtze River, it formed a WLFZ about 56.60km2, accounting for 16.27% of total WLFZ area in three-gorge reservoir after the reservoir accomplished. The ecological preservation and restoration of riparian belt are urgent problems for ecological environment protection in three-gorge reservoir, domestic and foreign experts believe that ecological restoring plant is a very effective way for damaged ecological system in riparian belt.Taking Pengxihe WLFZ basin in Three-Gorges Reservoir as survey area, the results showed that there were 146 vascular plant species belonging to 118 genera and 41 families, among of them Compositae and Gramineae were main plant in this zone. Geographic element analysis showed that the tropical plant species were the dominant ones for spatial patterns of seed plant species. Herbosa community in the WLFZ were including Xanthium sibiricum, Cynodon dactylon, Cyperus rotundus, Bidens frondosa+Conyza canadensis, Imperata cylindrical and so on. With SPSS software, clusters analysis have been carried out for herbosa communities from the level of altitudinal and time gradient, the results showed that vegetation distribution was a tendency to along the altitudinal and the community structure became more steadily with the succession of time. An analysis the relationship between community and environmental factors has been done by means of DCCA, and the results sowed that t altitudinal was the key factor which influencing vegetation distribution in WLFZ. Because of the area studied being very special, the altitudinal factor were basically reflecting the soil moisture status and nutrient content, the altitude also decided the basic community pattern in WLFZ of Pengxihe watershed. The time gradient’s variation characteristics of diversity index for vegetation in WLFZ appeared low-high-low with single peak curve form. The diversity index showed consistency between both altitudinal gradient and time gradient, and a low-high-low tendency with the altitudinal gradient from low to high. An analysis for niches of 25 dominant species has been made, and it showed that the species with more width niche was not always dominant species, such as Oxalis corniculata in May; while the species with more width niche was not always a higher overlap degree ones, such as Xanthium sibiricum, Cynodon dactylon. The niche overlap was not obvious since the competitiveness of species was strong, it would develop into greatly dominant species in community through competition to eliminate other ones. At the same time, species groups for the changes of niche overlap of main dominant species during May to September have been classified as well. Based on this research, some suggestions have been brought forward for species selection in the following Demonstration Base construction in the near future. |
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