Geographic Patterns of the Richness and Density of Wild Orchids in Nature Reserves of Jiangxi, China

Orchids have attracted much attention from researchers, because of their richness of species and their great ornamental and medicinal value. Jiangxi Province, which is located in southeastern China and ringed on three sides by mountains, contains many nature reserves and harbors large number of orchids. Here, we conducted field surveys of orchids in 35 nature reserves in Jiangxi, using sampling lines and plots. We also analyzed the relationship between orchid richness and density with environmental variables and studied the relationship among these nature reserves. We found that the mountainous areas of southwestern, southern, and northeastern Jiangxi have a high richness and density of orchids, while the mountainous areas of central and northwestern Jiangxi have low richness and density. Jiulianshan and Jinggangshan are the two most rich-species reserves, with 58 and 55 orchids, respectively. Eight reserves (22% of those surveyed) had fewer than 10 orchids. Compared with soil, climate, and vegetation, topography was more closely related to the richness and density of orchids. Topographical variables explained 19% and 20% of the total variation in SR and SD, respectively. The result of hierarchical clustering analysis showed that the 35 nature reserves of Jiangxi obviously fall into two main clusters, which are separated by the Ganjiang River-Poyang Lake water system. In conclusion, the geographical patterns of richness and the density of orchids in Jiangxi are uneven and are affected by topography and vegetation, while their distribution is affected by the terrain of Jiangxi. Our work explains the richness and density patterns and the assembly mechanism of the orchids in Jiangxi and also provides new ideas for the protection of orchids in this region.