CLASSIFICATION AND ORDINATION OF PLANT COMMUNITIES IN THE SOUTH OF SONG-NEN PLAIN
松嫩平原南部植物群落的分类和排序

In the south of the Song-Nen plain there is a temperate semimoist continental climate. The zonal vegetation in this region is meadow steppe. The distribution and combination of plants appear to be controlled mainly by the edaphic condition. Using qualitative and quantitative analyses, the vegetation can be divided into 11 communities. Based on ordination and biotope analyses, the 11 communities may be grouped into 5 ecological combinations: (1) The salt-alkali tolerant and hygrophilous combination, including the Sueada corniculata, the Sueada glauca and the Puccinellia tenuiflora communities; (2)The slightly salt-alkali tolerant and mesophilous combination, including the Leymus chinensis community; (3) The moisteutrophilous combination, including the Calamagrostis-Leymus, the Leymus-Potentilla and the Leymus-Hemarthria communities; (4) The Stipa baicalensis community on drainage rich soil; (5) The ammophilousxerophilous plant combination, including the Stipa grandis-Filifolium, the S. grandis and the Ulmus communities. As a example, a 2-dimensional ordination of 23 releves shows that the vegetation in the field is a mixture in varying proportions of continuity, and discontinuity In 2-dimensional ordination, the communities may be plotted according to the axes related to the saline content and alkalization of soil as well as soil moisture gradients in ordination field. The positions on each axis and the distance values between communities can quantitatively reflect the difference and relationship between communities.