Objective The coupling mechanism between stand structure and biodiversity is the important basis to innovate management techniques of plantations on basis of biodiversity conservation and improvement. However, the status of less research on the relationship between stand structure and woody plant diversity is the important bottleneck to managing urban forest scientifically. Therefore, taking the urban forest, which distributed within the sixth ring road in Beijing, as study objectives, and the aim of the study is to solve the affecting mechanisms of stand structure on woody plant diversity to provide theoretical supports for scientific establishing and managing urban forest.

Method Shannon-Wiener index, Margalef richness, Pielou evenness and Berger-Parker dominance were chosen to characterize the diversity of tree species composition, and average DBH, average tree height, diameter composition diversity, tree height composition diversity and stand basal area were chosen to describe the complexity of urban forest structure. Meanwhile, Pearson method was used to analyze the correlation between stand physical structure and woody plant composition, and principal component analysis was used to construct complexity indices to integratedly describe the relationship between stand physical structure and woody plant composition. Furthermore, the coupling degree between indices of stand physical structure and indices of woody plant species composition was analyzed.

Result (1) The species diversity of woody plants increased with the increase of tree height composition diversity and stand basal area, and decreased with enhancement of tree size while the influence of diameter composition diversity on woody plant species diversity was not significant. The higher woody plant species diversity was found in those urban forest stand with more complex vertical structure. (2) Woody plant diversity was significantly affected by complexity of vertical structure and complexity of space occupancy, while there was no remarkably relations between complexity of horizontal structure and complexity of woody plant composition.

Conclusion Woody plant species diversity is significantly affected by stand physical structure, and the main factors influencing woody plant species diversity were tree size and space occupancy, complexity of vertical structure. Thus it is suggested that enhancing complexity of vertical structure, tree size differentiation of inter- and intro-species and spatial heterogeneity of stably ecological species groups should be adopted to increase woody plant species diversity efficiently in establishing and managing urban forest activities, and then to improve the urban forest stability and integrated ecosystem services.