Vegetation of the water-level fluctuation zone in the Three Gorges Reservoir at the initial impoundment stage

The water-level of Three Gorges Reservoir first reached a normal storage level 175 m in October 2010, resulting in a large-area water-fluctuating zone with an elevation difference of 30 m (145–175 m). We used the Geographic Information System (GIS) technology, the field quadrat survey, the species importance value calculation, and literature data to assess the natural environment situation, the vegetation regeneration status, and the ecological benefits of the dominant plant species in terms of mitigating agricultural non-point source pollution of the WLFZ in the Three Gorges Reservoir at the initial impoundment stage. The results showed that: (1) the WLFZ area presented an obvious trend of increasing first and then decreasing from west to east, and the exposed area at the elevation intervals of 145–175 m, 155–175 m, and 165–175 m accounted for 20, 37.49, and 42.51% of the total area, respectively; (2) the WLFZ area gradually decreased with increasing gradient, and the exposed area at the gradient intervals of 60° accounted for 60.90, 18.62, 12.03, 8.06, and 0.39%, respectively, of the total area. (3) The vegetated area increased with increasing water level elevation, and the vegetation coverage area at elevation intervals of 145–155 m, 155–165 m, and 165–175 m accounted for 4.96, 16.09, and 44.77%, respectively, of the total area of the corresponding elevation interval. The vegetated area gradually decreased with increasing gradient, and at the sections Jiangjin-Changshou, Fuling-Yunyang, and Fengjie-Yiling, the vegetated area accounted for 15.30, 71, and 12.70%, respectively, of the total vegetation coverage area. (4) The important value calculation results indicate that the dominant species significantly differed among the different elevations in the three belt transects of the Yangtze River main stream (Zhongxian section), the Xiaojiang River (Kaizhou section), and the Xiangxi River (Guizhou section). The dominant annual herb species were Digitaria sanguinalis (Linn.) Scop., Conyza canadensis (Linn.) Cronq., Bidens frondosa Linn., Echinochloa crusgali (Linn.) Beauv., and Setaria viridis (Linn.) Beauv., while the dominant perennial herb species were Cynodon dactylon(Linn.) Pers. and Cyperus rotundus Linn.. (5) The water level elevation was the most important factor affecting vegetation restoration. At the initial impoundment stage, the naturally regenerating plant species Cynodon dactylon(Linn.) Pers. and Cyperus rotun