Abstract: In this paper, the spatial distribution pattern of arbors in 5 plots in the Usytu Nature Reserve was studied using the method of point pattern analysis. The results showed that the contagious distribution was the main spatial distribution pattern in the study area. A significant cluster distribution occurred in plot a and e under all the spatial scales; a random distribution occurred in plot b and d under small scale （r<8 m), but a cluster distribution occurred under large scale; a random distribution occurred in plot c under all scales. Diversity of herbaceous species under forest was analyzed using six different diversity indexes, the results revealed that there was a significant correlation between the diversity of herbaceous species and the spatial distribution pattern of arbors, that is the diversity of herbaceous species in the plots where a cluster distribution of arbors occurred was higher than that in the plots where a random distribution of arbors occurred.

Key words: arbor, spatial distribution pattern, cluster distribution, herbaceous species, diversity index, Usytu Nature Reserve, Inner Mongolia