Composition change and vegetation degradation of riparian forests in the altai plain,NW China

Riparian forests of the Altai Plain in China were studied usingDetrended Canonical Correspondence Analysis (DCCA) and Two-way Indictor SpeciesAnalysis (TWINSPAN). The species could be divided into hydrophytes,hygrophytes,hygro-mesophytes, xero-mesophytes, xerophytes, and high xerophytes. Riverrun-off, water table, and physical components of the soil decided thedistribution of the species. The forests could be classified into wood swamp,hygro-mesic forest, mesic forest and xeric forest. As a specific habitat in thedesert of northwest China, the river valleys harbored most of thePopulus and Salix species recorded inChina. However, the forest has been gradually invaded by adjacent desertspecies. Meanwhile, the native species diversity of the forest has beendeclining as the soil has become more saline and more xeric through intensiveirrigation practice and dam construction in the upper rivers.