Effect of three georges reservoir (Yangzi River) on the plant species richness in drawdown zone downstream the tributary river (Pengxihe River)

In order to understand the spatial pattern of plant community and the maintenance mechanism of biodiversity in littoral zone of Three Gorges Reservoir, 110 km stretches of Pengxihe River (from estuary to the backwater of Three Gorges) were chose to study. We investigated species composition and environmental variables along 50 m long stretches of riverbank between the high-water level and the lowest summer water level, at a 5 km interval. The results showed that: (1) along longitudinal gradients, longitudinal species richness, longitudinal shrub species richness and longitudinal herb species richness were significantly related to distance to estuary; (2) along lateral gradient, there were visible different changes in all kinds of types (lateral species richness, lateral tree species richness, lateral shrub species richness, lateral herb species richness). Along lateral gradient, species richness and herb species richness first increased with the elevation then reduced with it, trees and shrubs species richness increased with the elevation. (3) Correlation analyses showed that substrate types were correlated with the longitudinal species richness, without considering the distance to estuary. Soil moisture and substrate heterogeneity were correlated with lateral, species richness. These results indicated that, along longitudinal gradient of the river, distance to estuary plays an important role in species richness, and along lateral gradient spatial heterogeneity due to inundation and flooding plays an important role in forming a new pattern of plant community in the littoral zone of Three Gorges Reservoir Region. Because of special hydrological dynamics, plant in the littoral zone of Three Gorges, are gradually form a unique spatial pattern to some extent, though it had the same change law with riparian plant of a natural river.