Objective  Composition and diversity of the forest communities at the Caohai National Nature Reserve were studied to maximize the conservation of the natural resources.

  Method  In relatively concentrated and representative areas at the reserve, a survey was conducted on 16 lots, 20 m×30 m each in size, randomly selected following the typical sampling protocol. On each lot, 5 shrub plots sized 2 m×2 m each and 5 herb plots sized 1 m×1 m each were assigned along the diagonal line to observe the species, morphology, and varieties of the plants in a communities.

  Result  Totally, 74 species, 62 genera, and 34 families were found on the plots. Among them, 14 species were arbors; 23, bushes; and, 37, herbs. Species stratification was evident as the existing varieties of arbor class were dominated by Pinus yunnanensis, P. armandii, Cunninghamia lanceolata, Quercus aliena, Populus yunnanensis and Carpinus pubescens; whereas, the shrub and herb classes varied depending on the community type and eco-environment．All individual plants at the reserve showed a normal bell-shaped vertical distribution, a partially slant inversed J-shaped distribution on trunk-diameter, and an inverted J-shaped distribution on canopy-width, indicating constant and healthy growth of the forests. The 6 species that had their critical indicators scored greater than 5 with significant differences on the vertical, trunk and canopy structures. Both the richness and diversity indices of the communities ranked in the order of: herb class>shrub class>tree class, and the uniformity index: shrub class>herb class>tree class.

  Conclusion  Located at the apex on a land in transition from eastern Yunnan plateau to Guizhou plateau, the Caohai National Nature Reserve displayed the typical regional characteristic low variety and diversity but relatively stable composition of plants on its forest communities. There were numerous plants with sizable trunks in the C. lanceolate community that were declining and would continue to decline in number. The diversity on tree trunk-diameter of the C. pubescens community was exceedingly low, especially on plants with large trunk girth. Therefore, a special attention to protect and manage such communities needed be placed for forest conservation.