1. School of Soil and Water Conservation; Beijing Forestry University; Beijing 100083 PR China
2. Research Institute of Forest Ecology, Environment and Protection; Chinese Academy of Forestry; Beijing 100091 PR China
3. Urban Management Bureau of Futian District; Shenzhen 518049 PR China
4. Guizhou Academy of Forestry; Guiyang 550011 PR China
5. Department of Geography; University of Florida; Gainesville Florida 32608 USA