**2. Research area and survey method**

Beijing is the capital of China and the ancient capital of many dynasties in history. It is located in the north of North China Plain (39°28′–41°05'N, 115°25′–117°30′E), with a width of 160 km from east to west, a length of 176 km from north to south, and a total area of 16410.54km2 , under the jurisdiction of 16 municipal districts. It is adjacent to Tianjin and surrounded by Hebei Province together with Tianjin, bordering

#### *Assessment of Urban Biodiversity: A Case Study of Beijing City, China DOI: http://dx.doi.org/10.5772/intechopen.106264*

Yanshan Mountain and Inner Mongolia Plateau in the north, Huang-Huai-Hai Plain in the south, Taihang Mountain and Shanxi Plateau in the west, and Songliao Plain in the northeast. It is generally divided into three geomorphic units: western mountain, northern mountain, and southeast plain. Beijing has a typical warm temperate semihumid continental monsoon climate, with an annual average temperature of 12.77°C (1978–2013) and an average annual precipitation of 548.86 mm (1978–2013). Though affected by the terrain, climate, soil, and other conditions, Beijing is rich in natural vegetation types, showing regular vertical distribution and transitional alternation. The main zonal vegetation is the warm temperate deciduous broad-leaved forest and the distribution of temperate coniferous forest. However, as an international metropolis, there are few natural communities in the urban area, and there are relatively many kinds of artificially planted plants.

The plant communities of three main types of green space in the parks, streets, and residential areas in each ring of the built-up area in Beijing are selected. Mechanical point method is used to conduct sample point survey within the 6th ring of the built-up area in Beijing. The lines are drawn from the center to the east, west, south, and north (i.e., "two axes"—along the east-west axis of Chang'an Street and the north-south axis perpendicular to it), and select appropriate parks, streets, and residential areas in four directions to conduct plant diversity surveys (three sample points were selected for different green space types within the 2nd ring). A total of 19 parks, 19 residential areas, and 19 streets were selected. A total of 57 transects were investigated in the street, and 114 arbor quadrats, 456 shrub quadrats, and 456 herb quadrats were surveyed in parks and residential areas.

The overall situation of the park green space, residential green space, and street green space in the selected sample points is inspected, and the types of plants, life forms, and whether they are introduced species appearing in the green space were recorded. Among them, all plant species in the park green space and residential green space were recorded, and 100 m transect was selected for each street to record all plant species. According to the method recommended by Fang et al. [41], three tree quadrats of 10 m × 10 m were selected in each park green space and residential green space, and four 5 m × 5 m shrub quadrats and four 1 m × 1 m herb quadrats were selected from each tree quadrat (shrub and herb quadrats were selected from tree quadrats, respectively).
