Abstract: There are 124 understory species in the 662 sampled plots, belonging to 37 families and 91 genera, of which 54 are endemic to China, in the herb community in Huanglong valley, southwestern China.In total, thirty-three orchid species of 21 genera were recorded, of which 12 species are endemic to China and one is new It is interesting that so many terrestrial orchids appear in a small area (ca. 1 km²). Furthermore, some of the orchid species are dominant in the herb community. Most of the species, including orchid, have low frequency and uneven distribution patterns. The results indicated that the orchid species in Huanglong valley may disperse with regard to resource usage. Orchid species distributed mainly in two different habitats, i.e. travertine areas and the remained forest. The microenvironmental conditions and the orchid species compositions were found to be quite different between these two habitats. Travertine areas had a higher number of orchid species as well as higher numbers of orchid species per plot as compared to forest. In the travertine areas, 30 orchid species were found; the most common ones being Cypripedium bardolphianum, C.flavum, C.tibeticum, G.diantha, Phaius chusua and Ph. delavayi. However, in the forested habitat, 21 orchid species were found; the most common ones being T.szechuanica and Goodyera repens. Light availability seems critical to the performance and distribution of orchid species. Stream flow through the travertine area during the orchids growing season appears to be an important factor in shaping and maintaining stable microenvironments which favorable to the growth and reproduction of orchids. The results suggest that some orchid species in the travertine area would be threatened if the travertine stream flows were changed or disrupted.

Key words: orchid species, diversity, community structure, conservation