内蒙古草原植物的生态替代及其对全球变化了草原动态的指示

在内蒙古草原区，从荒漠草原带到森林草原带，沿气候干燥度变化的方向调查了１１９个草原样地的植被与环境特征，依此定量分析了植被－环境关系。根据表述环境因子取样质量的环境因子墒值及环境因子与出现频率最高的５０个植物种间的平均相互信息，分析了所调查３０个环境因子在决定植被组成中的作用优势度。结果表明，气候因子的影响是占绝对优势的，而地形和管理因子的作用是次一级的，或是地区性的。群落的物种组成与其第一优势种关联极好，因而依群落第一优势种识别的植物群落类型是组成和结构相对稳定的群落单位。基于植物种在降水和气温梯度上最适区域的计算及依此在植物降水－气温平面上的直接排序，揭示出广泛的草原植物在气候梯度上的生态替代。这种替代，尤其是包括针茅属（Ｓｔｉｐａ）植物在内的草原优势植物的替代，导致了针茅草原的生态替代。本研究也定量刻划了内蒙古主要草原植物群落的植被特征，及其在气候、土壤和人为影响梯度上的分布幅度和生态适宜区域。草原植物种和植物群落在气候和放牧梯度上的直接排序提供了气候和土地利用变化后草原植被动态的可能图景。

ECOLOGICAL VICARIANCE OF STEPPE SPECIES AND COMMUNITIES ON CLIMATE GRADIENT IN INNER MONGOLIA AND ITS INDICATION TO STEPPE DYNAMICS UNDER THE GLOBAL CHANGE

Based on the investigation of the vegetation and environment in 119 sites along an itinerary from the desert-steppe transition zone to that offorest-steppe in Inner Mongolia steppe region, the vegetation environment relationships were quantitatively analyzed.The preponderance of the 30 factors in determination of vegetation composition were hierachized according to their sampling quality and their mutual information with the 50 most frequent spedes. The result showed that climate was the most preponderant; while the topographic and managerial factors were secondaryor local. The community composition was well associated with the first dominant spedes, so the dominance community-type ldentlfled according to the first dominant spedes was the relatively stable unit of similar composition and structure.The ecological vicariance of a large amount of steppe specles along climate gradient were revealed by an ordination of these spedes on a precipitation-temperature plane according tothelr preference to these 2 factors. This vicariance, especially the vicariance of the dominant species including a group of Stipa specie, resulted in the vicariance of the Stipa communities. The traits of the main steppe communities were characterized by presentation of their preference and amplitude on the climate, soil and grazing gradient, and by synthesls of their vegetation features. The direct ordination of the spedes and communities along the gradients of climate and grazing intensities provided adynamic scenario of the stePPe vegetation under the climate and landuse changes.