1. State Key Laboratory of Vegetation and Environmental Change; Institute of Botany; Chinese Academy of Sciences; Beijing 100093 China
2. University of Chinese Academy of Sciences; Beijing 100049 China
3. State Key Laboratory of Forest and Soil Ecology; Institute of Applied Ecology; Chinese Academy of Sciences; Shenyang 110164 China
4. Department of Biology; Graduate Degree Program in Ecology; Colorado State University; Fort Collins Colorado 80523 USA
5. Department of Botany and Microbiology; University of Oklahoma; Norman OK USA
6. Department of Forest Ecology and Management; Swedish University of Agricultural Sciences; Umeå 901 83 Sweden