1. Central China Normal Univ., Hubei Province Key Lab. for Geographical Process Analysis and Simulation, School of Urban and Environmental Science 152 Luoyu Road Wuhan Hubei Province 430079 China
2. Rangeland Resources and Systems Research Unit USDA‐ARS 2150 Centre Ave, Bldg D Fort Collins CO 80526
3. Dep. of Plant and Soil Sciences Univ. of Kentucky 1100 Nicholasville Road Lexington 40546