1. Key Laboratory of National Forestry & Grassland Administration on Forest Resources Conservation and Ecological Safety in the Upper Reaches of the Yangtze River, College of ForestrySichuan Agricultural University Chengdu 611130 China
2. Department of Resources and Environmental EngineeringSichuan Water Conservancy Vocational College Chongzhou 611845 China
3. College of Landscape ArchitectureSichuan Agricultural University Chengdu 611130 China