中文摘要：

基于内蒙古地区草原植物群落样带调查,采用双向指示种分析（TWINSAPN）、除趋势对应分析（DCA）、多元回归树（MRT）和典范对应分析（CCA）等方法,探讨了群落组成、分布格局及影响其分异的主导环境因子.结果如下：1）TWINSPAN将273个群落调查样方划分为8个群系级草原类型,各自代表并反映出该地区草原群落的特点;2）DCA排序结果间接地反映出群落类型与环境梯度之间的关系,CCA排序结果较好地展示了各群落类型中优势物种的生境特征,并进一步展示了该地区草原类型、主要物种与环境因子的响应关系;3）DCA、MRT及CCA结果均表明,气候因素对于该地区草原植被的地域分异影响作用较大,其中水分因子的影响十分突出,特别是最湿月、最暖季节与最冷季节降水,是构成内蒙草原植被类型区域分异的决定性因素;4）MRT与CCA结合使用能进一步挖掘出更多的环境信息,为群落分布格局的形成原因提供更深入更全面的环境解释.

英文摘要：

Various temperate steppe communities are present in the Inner Mongolian Plateau region from northeast towards southwest in Northern China,largely owing to regional heterogeneous environment with sharp water and thermal gradients as well as spatially-differentiated soil types.To study influence of those regional and local environmental factors on distribution and differentiation pattern of steppe vegetation,relationships between community features and environmental factors were analyzed.Vegetation data were sampled from 273 plots along a 1 500 km belt transect,climatic and soil data were obtained from field survey or collected with GIS tools.TWINSPAN（two-way indicator species analysis）was used to classify vegetation,DCA（detrended correspondence analysis）was used to examine and validate differentiation among those vegetation formations.Classification by TWINSPAN,MRT（multivariate regression trees）was used to select key environmental factors greatly influencing distribution and composition of communities.CCA（canonical correspondence analysis）was used to interpret the most prominent environmental factors dominating spatial differentiation of vegetation types as well as their species composition features.Those 273 plots surveyed along the belt transect could be clearly classified into 8vegetation formations belonging to 3vegetation subtypes,each could characterize and stand for a special kind of grassland habitats.DCA ordination implied some relationships between steppe communities and environment gradients. Moisture gradient（represented by precipitation regime）from southwest up to northeast,partly along with thermal gradient（represented by the temperature regime）in the same direction,seemed to function as the most prominent factor influencing distribution and differentiation of regional steppe communities.Distribution pattern of 23 dominant species revealed by CCA ordination clearly demonstrated chief environmental factors dominating differentiation of steppe communities.DCA ordination,MRT and