1. School of Soil and Water Conservation; Beijing Forestry Univ.; Beijing People's Republic of China 100083
2. Dep. of Ecology; Evolution and Natural Resources, Rutgers Univ.; New Brunswick NJ 08901
3. Key Lab of Ecosystem Network Observation and Modeling; Institute of Geographic Sciences and Natural Resources, Chinese Academy of Sciences; Beijing People's Republic of China 100101
4. Dep. of Plant Biology and Pathology; Rutgers Univ.; New Brunswick NJ 08901