EFFECTS OF DAM IMPOUNDMENT ON LAKESIDE VEGETATION SUCCESSION IN THE PLATEAU WETLANDS OF THE LASHI LAKE

The Lashi lake,a typical wetland in the upstream of the Yangtze River was selected to study the effects of dam impoundment on the characteristics and distribution patterns of vegetation by the methods of traditional field survey combining with locate study.The results showed that there were 97 species of vascular plants in the studying area belonging to 34 families and 76 genera.The vegetation could be divided into 2 types,3 subtypes and 10 communities.The vegetation distribution pattern and composition structure alternated obviously.The proportions of swamp,meadow and aquatic plants in the study area were changed from 44.54%,18.69% and 36.76%,respectively in 2009 to 32.59%,13.68% and 53.59%,respectively in 2011.The area of meadow and swamp shrank as dam impounding while the area of aquatic plant expanded gradually.The dominant species of Artemisia in the meadow was replaced by Cynodon dactylon gradually.And the community of Leersia hexandra became the main component in the study area.The vegetation succession model was meadow(weeds community,Cynodon dactylon community) to swamp(Juncus allioides community,Acorus calamus community,Eleocharis vallcculosa community,Polygonum hydropiper community) to aquatic vegetation(Leersia hexandra community,Polygonum amphibium community,Azolla imbricate community,Potamogeton distinctus-Myriophyllum spicatum community) following the dam impounding.The measure of dam impoundment made the Lashi lake vegetation succession reversely,which prolonged the life of the lake wetland but its effects on fish,waterfowl,and the wetland ecological structure and ecological service need further study.