1. Department of Ecology College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education Peking University 5 Yiheyuan Road Beijing 100871 China
2. Rubenstein School of Environment and Natural Resources University of Vermont Burlington Vermont 05405 USA
3. Key Laboratory of Adaptation and Evolution of Plateau Biota Northwest Institute of Plateau Biology Chinese Academy of Sciences 23 Xinning Road Xining 810008 China
4. State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 China
5. The Arnold Arboretum of Harvard University 1300 Centre Street Boston Massachusetts 02131 USA
6. State Key Laboratory of Forest and Soil Ecology Institute of Applied Ecology Chinese Academy of Sciences Shenyang 110164 China