1. Center for Documentation and Information, Institute of Botany, Chinese Academy of Sciences , Beijing 100093 , China
2. School of Ecology and Nature Conservation, Beijing Forestry University , Beijing 100083 , China
3. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences , Beijing 100093 , China
4. Department of Geography, Remote Sensing Laboratories, University of Zurich , 8057 Zurich , Switzerland