1. Center for Chinese Agricultural Policy, Institute of Geographical Sciences and Natural Resource Research, Chinese Academy of Sciences, Jia 11, Datun Road, Beijing 100101, China.
2. Department of Agricultural and Resource Economics, University of California, 1 Shields Avenue, Davis, CA 95616, USA.
3. Department of Agricultural, Food, and Resource Economics, Rutgers University, 55 Dudley Road, New Brunswick, NJ 08901–8520, USA.