Abstract: Understanding the influence of stand factors on species diversity of herb layer in forest plantations is of great significance for forest tending and rational management. In this study, we investigated six stand factors (i.e., stand death rate, average tree height, average branch height, average diameter at breast height, average crown width, and stand density) and community characteristics of herb layer in Zhangbei poplar plantations. The species diversity indices of herb layer were calculated to analyze the changes in stand structure and species diversity of herb layer with changes of stand factors. The results showed that 44 species of vascular plants in herb layer were found, belonging to 38 genera of 17 families. The top three families with the most species were Compositae, Leguminosae and Gramineae. Xerophytes were the dominant ecological water type of plants, with a total of 25 species accounting for 56.82% of all species. Hemicryptophyte, a total of 27 species, was the dominant life form in herb layer, which accounted for 61.36% of the total species. The species richness index, Shannon index and Pielou index varied among different plots, with species richness index having the largest coefficient of variation (CV). Simpson index did not vary among different plots, with a minimal CV. There were significant differences in the stand factors among various plots, among which the degree of variation of stand death rate was the highest, and the variation degree of average diameter at breast height was the lowest. The main stand factors affecting species richness index of herb layer were stand death rate, average branch height, average diameter at breast height and stand density. The main stand factors affecting the Shannon index were stand death rate, average tree height, average diameter at breast height and stand density. Stand factors had no effects on Simpson index and Pielou index. Appropriate regulation of stand density and mixture of poplar with conifer species would be beneficial to the maintenance of species diversity of herb layer in Zhangbei poplar plantations.

Key words: urban and rural settlements, spatial differentiation, Tibet, influencing factor, agglomeration distribution