VERTICAL DIFFERENCE OF THE VEGETATION IN THE MIDDLE AND UPPER REACHES OF XUNHE RIVER BASIN ON THE SOUTH FACE OF QINLING MOUNTAIN

The upper and middle reaches of Xunhe River basin is located in the south face of Qinling Mountain.The vertical difference of the vegetation in the region is studied through field works in order to understand the vegetation in the Qinling Mountain deeply and provide scientific basis for rational development and utilization of the vegetation resources.The vegetation in this region can be divided into three vertical zones:the mid and low_mountain typical deciduous broad_leaved forest zone,the mid_mountain deciduous little broad_leaved forest zone,and the sub_alpine coniferous forest zone.The plant species and vegetation types in the three vertical zones are different from each other,and their numbers decrease with increasing altitude.The proportion of tropical genera to all genera of the mid and low_mountain typical deciduous broad_leaved forest zone is larger than those of other two zones,but the proportions of the temperature genera are almost the same in all zones.The proportions of phanerophytes,hemicryptophytes and cryptophytes are the largest in the mid_mountatin deciduous little broad_leaves forest zone,the mid_mountain deciduous little broad_leaved forest zone,and the sub_alpine coniferous forest zone,respectively.The three zones are different in bare land types,initiative succession communities,pioneer forests and climax communities.The vegetation resources in this region should be protected and rationally utilized according to the conditions of each vertical zone.In the mid—and low_mountain typical deciduous broad_leaved forest zone,firewood forests and commercial forests should be expanded at the Quercus variabilis sub_zone,and the Q.aliena var.Acuteserraeta sub_zone should be built into a timber forest base .The Betula albo_sinensis forests on the gentle slopes may be cut ,but those on the steep slopes should be forbidden to be fall within the mid_mountain deciduous little broad_leaved forest zone.All the forests in the sub_alpine coniferous forest zone should be protected as forests for the conservation of water.eneraareal