1. School of Landscape Architecture, Beijing Forestry Univ., 35 Qinghua East Rd., Haidian District, Beijing 100083, China.
2. Researcher, Yangtze River Industrial Economic Research Institute, Nanjing Univ., Jiangsu 210093, China (corresponding author).
3. School of Landscape Architecture, Beijing Forestry Univ.; Professor, Beijing Forestry Univ., 35 Qinghua East Rd., Haidian District, Beijing 100083, China.