WU, DONGHUI, Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China. Key laboratory for vegetation ecology, ministry of education, Northeast Normal University, 130117 Changchun, China Jilin Provincial Key Laboratory of Animal Resource Conservation and Utilization, Northeast Normal University, 130117, Changchun, China.