1. School of Ecology and Nature Conservation, Beijing Forestry University , Beijing 100083 , China
2. The Key Laboratory of Ecological Protection in the Yellow River Basin of National Forestry and Grassland Administration , Beijing 100083 , China
3. College of Agriculture, Purdue University , West Lafayette, IN 47907 , USA
4. Biological Systems Engineering, Florida A&M University , Tallahassee, FL 32310 , USA
5. Wetland Research Centre of Beijing Forestry University , Beijing 100083 , China