Abstract: The structure of urban forest determines the appearance and total green biomass of urban forest and consequently its eco-efficiency. A stratified sampling survey was conducted on the urban forest within the range from 1 km outside the Sixth Ring Road to the center of Beijing to analyze species diversity and arbor specifications and their spatial variation, and find out current problems and variation pattern in gradient, with the aim to provide reference for the diversity conservation and scientific management of Beijing’s urban forests. Through a survey of 847 plots of various types of urban forests, we recorded woody plants of 50 families, 106 genera and 159 species, 75% of which are indigenous species. The urban forest communities are dominated by a few species. Populus tomentosaCarr. and Sophora japonica L. are the tree species used most in quantity (9.7%) and most frequently (28.45%). For arbors, the average DBH is 19.79 cm and the average crown breadth is 5.4 m. The overall specification is small with limited difference. The urban forests in Beijing showed an obvious change in gradient from the inside to the outside towards the direction of urban development. Species richness outside 4th Road is higher than that inside, with the highest richness of 112 species within 4th-5th Roads. The diversity and homogeneity gradually decreased. The arbor specification becomes smaller. Species composition, diversity, and arbor specification in “six urban districts” are better than those of other administrative areas.

Key words: Tibetan antelope, ecological corridor, human disturbance, alpine desert, QinghaiTibet Plateau.