1. School of Geographic Science and Remote Sensing, Guangzhou University, Guangzhou 510006, China
2. State Key Laboratory of Black Soils Conservation and Utilization, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China
3. College of Geographical Sciences, Harbin Normal University, Harbin 150025, China
4. School of Public Administration and Law, Northeast Agricultural University, Harbin 150030, China