1.College of Soil and Water Conservation,Beijing Forestry University,100083,Beijing;2.Inner Mongolia Research Academy of Forestry Sciences,010010,Hohhot;3.Forestry Bureau of Aohan Banner in Inner Mongolia,024300,Aohan,Inner Mongolia;4.Inner Mongolia Agricultural University,010010,Hohhot;5.Ningxia Institute of Forest Inventory and Planning,750001,Yinchuan: China