关键词: 幂函数法则, 频度, 种群分布, 空间异质性, 放牧梯度

Abstract: We compared the occurrence frequencies and spatial heterogeneity of individual plant species at three grassland sites with different grazing intensity in the northeast Inner Mongolian steppe. We arranged 3 transects 50 m long at three sites with light grazing, moderate grazing, and heavy grazing, in which 100 quadrats of 50 cm×50 cm (composed of four 25 cm×25 cm cells) were arranged. All species occurring in each cell were recorded by name and were analyzed using a power-law model. The most frequent species were Bassia dasyphylla and Leymus chinense in the lightly grazed site, Chenopodiaceae album and Cleistogenes squarrosa in the moderately grazed site, and Salsola collina and Allium polyrhizum in the heavily grazed site. At the community level, the species richness and the spatial heterogeneity, evaluated based on the frequency of occurrence, decreased with increased grazing intensity. The spatial heterogeneity at the species level tended to increased with increased grazing intensity. These results indicated that with higher grazing intensity, communities and the species in those communities were more fragmented, more aggregated, and contained more exclusive crowds. These characteristics in each species and the three communities appeared to be related to the reproduction strategies, life history, and physio-ecological characteristics of each species.

Key words: power-law, species occurrence, population distribution, spatial heterogeneity, grazing gradient