1. State Key Laboratory of Forest and Soil Ecology; Institute of Applied Ecology; Chinese Academy of Sciences; Shenyang 110164 China
2. Key Laboratory of Water Environment Evolution and Pollution Control in Three Gorges Reservoir; Chongqing Three Gorges University; Wanzhou 404100 China
3. University of Chinese Academy of Sciences; Beijing 100049 China
4. Department of Ecology; College of Urban and Environmental Sciences; and Key Laboratory for Earth Surface Processes of the Ministry of Education; Peking University; Beijing 100871 China
5. Environmental Studies Department; University of California; Santa Cruz CA 95064 USA