Aboveground Biomass of a Naturaly-regenerated Schima superba Community at Xiaokeng of the Nanling Mountain Aboveground biomass of natural Castanopsis fissa community at the Xiaokeng of NanLing Mountain, Southern China Arbuscular mycorrhizal status of Glomus plants in tropical secondary forest or Xishuangbanna, Southwest China Study on the Change of Soil Nutrient Before and After Burning Secondary Forest in Xishuangbanna THE UTILIZATION OF TROPICAL SECONDARY FOREST AND THE CHANGE OF SOIL PHYSICAL PROPERTIES