RIPARIAN PLANTS IN THE MAINSTREAM OF THE YELLOW RIVER:ASSEMBLAGE CHARACTERISTICS AND ITS INFLUENCING FACTORS

Riparian vegetation,as a key component of riparian ecosystem,offers suitable habitat and migrating or dif-fusing corridor for animals and plants,and has an important function in buffering and filtrating non-point pollution.The Yellow River is an important wetland in China,and also an essential zone supporting biodiversity.However,the devel-opment of riparian vegetation along the Yellow River is threatened by flow regime alteration caused by the overexploi-tation of water resources such as agricultural irrigation and hydraulic engineering construction.Embankment along the lower river is also destroying the habitats of the riparian vegetation.However,previous researches on the riparian vege-tation along the Yellow River focused on only some specific area.To ensure a deep understanding of the present status of the riparian vegetation and provide support for the protection of riparian vegetation diversity and the riparian man-agement of the Yellow River,two systematic surveys were carried out in April to June and September to October,2008,respectively.The species composition and species diversity of riparian plant communities were analyzed.Classifications of the vegetation by two way indicator species analysis(TWINSPAN) were also carried out.Altogether 169 species belonging to 37 families and 124 genera were recorded.Floristic analysis showed that the flora had diverse geographical origins.With regard to the spatial distribution,the herbaceous plants in the middle river sections were more abundant than those in the upper and lower river sections both in biomass and density.TWINSPAN classification divided the vegetation into 17 communities.The characteristics of the communities were described.The correlative analyses indi-cated that altitude,annual mean temperature,annual mean rainfall,annual mean runoff,mean maximum velocity were the main factors influencing the structure and distribution of the assemblages.