1. Department of Geography; Humboldt-Universität zu Berlin; Unter den Linden 6 10099 Berlin Germany
2. Leibniz Centre for Agricultural Landscape Research (ZALF); Eberswalder Straße 84 15374 Müncheberg Germany
3. Institute of Geographic Sciences and Natural Resources Research; Chinese Academy of Sciences; Beijing 100101 China
4. State Key Laboratory of Resources and Environmental Information System; Beijing 100101 China