Abstract: [Objective] This paper presents an analysis and comprehension of the diversity and structural characteristics of woody plants in the greenbelt attached to urban roads in the Sixth Ring Road of Beijing from two aspects, comprehensively sort out the current situation of urban greening campaign in Beijing, in order to find the problems and gradient changes and provide basic sample data for further dynamic research.[Method]Based on the 0.5 m World View 2 remote sensing image, the roads within 1km outside the 6th Ring Road in Beijing were visually interpreted. Meanwhile, ArcGIS was used to randomly select field survey road sections for the named roads in the area through taking 10% of the total length of each type of roads as the survey length. Woody plant species, DBH, crown breadth and other indicators were investigated for the selected road sections, and the species diversity and tree structure were analyzed. Result]This study recorded a total of 33 families, 61 genera and 77 species of woody plants in the green spaces along the roads in Beijing, including 59 tree species, 15 shrub species and 3 vine species. The most common tree species was Sophora japonica (Japanese pagoda tree), and there were 62 native species in Beijing. The richness and species diversity showed a gradual trend of increase from the inside to the outside of the city along the ring roads. The mean DBH of trees was 24.07 cm, which decreased gradually from the inside to the outside of the city along the ring roads, and the number of the DBH of trees in the grade Ⅱ was the largest. The overall proportion of larger diameter class trees gradually decreases from the inside to the outside of the city, and it was also higher along national roads and hutongs than that of other types of roads. The average crown breadth of trees was 6.33 m, and the crown breadth of grade IV, i.e. 6-8 m, was the most common. The crown breadth of trees between ring roads gradually decreases from the inside to the outside of the city. Among all the types of roads, trees with a large crown breadth along national highways and hutongs occupy a large proportion.[Conclusion]The species diversity in the green spaces along the roads in Beijing is not high, and the dominant tree species is widely planted, especially S. japonica, as Beijing's city tree, its number and frequency are much higher than those of other tree species. The proportion of maturing trees is relatively high, with an uneven distribution, but there are too few juvenile trees, with no necessary supplementary plantings in the later period. The overall crown cover is good, and the crown breadth is distributed evenly in different grades. The green spaces along the roads in Beijing is obviously affected by the process of urbanization, along the ring roads, there is a gradual increase in the change of species and a decrease in the specifications from the inside to the outside of the city. The species richness along urban roads (ring road, main road, secondary main road, branch road, Hutong) is obviously higher than that of roads in the outskirts (expressway, national highway, provincial road,). The larger diameter class trees are mostly distributed along national roads and hutongs, and the crown breadth of trees along roads on the outskirts is larger than that along urban roads.

Key words: road, Beijing, diversity, structure, ring road, type