Abstract:

The analysis of landscape structure in the Dongting Lake region by remote sensing interpretation indicates that the wetlands structure changed significantly in the past 20 years.Among the four major types of classification (i.e.reed,grass,water and mudflat),the distribution area of reed increased steadily (from 475 km2 to 751 km2),the area of grass was relatively stable,the area of water and mudflat was substantially reduced.In this process,some grass communities were replaced with the reed communities,and the grass communities invaded the mudflat areas.Sediment and hydrological regime were two main factors affecting the change of landscape pattern in Dongting Lake wetlands,but this situation changed after 2000 with the impact of sharp reduction in sediments and prolonged low flow period.Analysis by coupled hydrological calculation and spatial analysis on landscape reveals that although the elevations for different type of vegetation covers varied in different regions,their inundation patterns were much similar.Sediment and hydrological regime changes had triggered vegetation succession by changing the wetland inundation patterns.The operation of the Three Gorges Reservior had shortened the inundation period of middlelower wetlands,which in turn resulted in the grass invasion to water area up to 05 m