1. School of Natural Resources and the Environment University of Arizona Tucson AZ 85721 U.S.A.
2. Institute of Environment and Sustainable Development in Agriculture Chinese Academy of Agricultural Sciences Beijing 100081 China
3. Institute of Ecology, College of Urban and Environmental Science and Key Laboratory for Earth Surface Processes of the Ministry of Education Peking University Beijing 100871 China
4. DAPPER Stats Portland OR 97212 U.S.A.