内蒙古高原东南缘森林草原过渡带景观的若干特征

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

内蒙古高原东南缘森林草原过渡带位于中国东部暖温带落叶阔叶林向温带草原过渡的区域 ,本研究区的范围为 115°45′～ 117°45′ E,42°0 0′～ 43°45′ N。以群落分类和分布规律为主要依据 ,利用遥感影象 ,划分了研究区内的植被界线 ,并分析了过渡带内部植被的空间分异。结果表明 :研究区内森林带、过渡带和草原带的界线明显 ,过渡带内部由于地貌条件的差异可进一步划分为高原边缘山地森林草甸景观、高原森林草原景观和山地森林草原景观。从东南向西北做一条样带 ,可以发现 ,从森林到森林草甸 ,进而到森林草原和草原 ,物种的递变明显。森林带有大量的本带特有的种类 ,这些种类为暖温带落叶阔叶林北部的常见种类 ,说明本区的落叶阔叶林并没有处在落叶阔叶林带的气候边缘 ,而是由于地貌的变化才迅速向森林草甸进而向森林草原过渡 ;高原边缘山地森林草甸景观与高原森林草原景观的共有种类少 ,二者各自均有大量特有种。从森林带过渡到高原边缘山地森林草甸 ,水热组合由暖湿向冷湿方向发展 ,这种变化是由坝缘山地的迅速升高所引起的。从高原边缘山地森林草甸过渡到高原森林草原 ,温度状况逐渐好转而降水量呈逐渐下降的趋势 。

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.