College of Forestry, Gansu Agricultural University, Lanzhou, Gansu 730070, China;
College of Forestry, Gansu Agricultural University, Lanzhou, Gansu 730070, China;
College of Forestry, Gansu Agricultural University, Lanzhou, Gansu 730070, China;
College of Forestry, Gansu Agricultural University, Lanzhou, Gansu 730070, China;