LANDSCAPE FEATURES OF THE FOREST-STEPPE ECOTONE ON THE SOUTHEASTERN EDGE OF THE INNER MONGOLIA PLATEAU

The forest steppe ecotone at the southeastern edge of the Inner Mongolia Plateau is located at the transitional zone between the deciduous broad leaved forest zone in the eastern part of China and the steppe zone. The vegetation boundaries of the study area (115°45′ 117°45′E 42°00′ 43°45′N) were delimited using remotely sensed images according to characteristics and distributions of plant communities. The ecotone can be divided into three landscape units: forest grassland on the mountains at the edge of the plateau, woodland steppe on the plateau and mountainous woodland steppe. High species turnover was found between each pair of zones as well as between the forest grassland landscape and woodland steppe landscape. There are a large number of endemic species in the forest zone, which indicates that the broad leaved forest has not reached its climate determined edge. Between the forest and forest grassland zones, the climate changes from warm and humid to cold and humid with the rapidly rising mountains at the edge of the plateau. From forest grassland on the mountains at the edge of the plateau to woodland steppe on the plateau, the temperature becomes increasingly milder while the precipitation decreases. From woodland steppe on the plateau to steppe zone, the precipitation gradually decreases but temperature has no obvious change. Insufficient water supply is the principle factor for the lack of trees in the steppe zone. The vegetation at the forest steppe ecotone is a mosaic of forest and steppe/grassland. The results of this field survey show that the Ulmus pumila open forest should not be assigned to the forest steppe landscape. Instead, it must be regarded as an extra zonal distribution within the steppe zone.