1. College of Forestry, Sichuan Agricultural University, Chengdu 611130, China
2. Key Laboratory of Forest Protection of Sichuan Education Department, Sichuan Agricultural University, Chengdu 611130, China
3. Key Laboratory of National Forestry & Grassland Administration on Forest Resources Conservation and Ecological Safety in the Upper Reaches of the Yangtze River, Sichuan Agricultural University, Chengdu 611130, China