Abstract: In the area (24°39′-30°08′N, 108°47′-114°15′E),the root systems of 68 trees belonging to 12 tree species were investigated to furnish the scientific basis of tree species selection for planting in the water-eroded lands.By the combiming method of qualitative and quantitative,the ecological adaptability of common tree species to the water-eroded lands in the subtropical zone were evaluated.The conclusions were:1.The limit of ecological adaptation for 20 tree species to soil layer depth were worked out.The limit of 0-5cm was for Pinus massoniana,P.taeda,P.elliotii,Liqiuidambar formosana,Robinia pseudoacacia,Pistacia chinensis,Quercus fabri,Q.acutissima,Q.chenii,Castanea henuyi,Cyclobalanopsis glauca,6-20cm for Q. rariabilis,Dalbergia hupeana,Schima superba,Nyssa sinensis, Cupressus funebris,Ziziphus juiuna,Myrica rubra;and 21-30cm for Cunninghamia lanceolata, Sassafras tzumu.The root traits of the tree species which have the minimum limit of the ecological adaptation are as follows:The larger area,the deeper distribution and creeping on the shallow layer of soil and developing along the crevice of rock in soil.2.Using Quantification theory (I)the relationship between 11 tree species and ecological factors,and the adaptability of plants to the ecological factors were found out.According to their contribution to the plant growth,the order of the ecological factors were arranged.In addition,we found that the soil layer,soil layer plus parent material and slope were the most important factors to the growth of plants in water-eroded land.

Key words: Water-eroaed, Afforesting tree species, Ecological adaptability