1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, CAS and MWR, Yangling, Shaanxi 712100, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
3. Institute of Soil and Water Conservation, Northwest A&F University, Yangling, Shaanxi 712100, China
4. Department of Forestry, Mississippi State University, Starkville, MS 39759, USA