1. Institute of Resources and Energy Research, Baotou Teachers’ College, Inner Mongolia University of Science and Technology, 3 Science Road, Baotou 014030, China
2. School of Economics and Management, Baotou Teachers’ College, Inner Mongolia University of Science and Technology, 3 Science Road, Baotou 014030, China
3. Department of Forest and Wildlife Ecology, University of Wisconsin-Madison, 1630 Linden Dr., Madison, WI 53706, USA
4. Faculty of Art and Science, University of Toronto-St. George Campus, 27 King’s College Cir, Toronto, ON M5S 1A1, Canada
5. School of Economics and Management, Northeast Forestry University, 26 Hexing Road, Harbin 150006, China