Distribution pattern, composition, and diversity of the Rubiaceae species along the altitudinal gradient of the Himalayas in Western Bhutan

摘要

The study conducted along the altitudinal gradient of 300-3900 m asl. recorded a total of 36 species (21 genera) and 46species (29 genera) in study areas I and II respectively. The sighting of only one species each for the majority of genera,including Pavetta L., Oldenlandia L., and Argostemma Wall., which are described as the largest genera of Rubiaceae, wasunusual. While the species with a narrow distribution range were found concentrated at the lower altitude exhibiting endemicnature, the herbaceous species exhibiting maximum distribution range were dominant at the higher altitudinal range. The lowaltitudinal hump-shaped distribution pattern was observed in both study areas. The higher diversity indicated by the Shannon-Wiener and Simpson diversity analysis was attributed to the moderate mean precipitation, temperature, and relative humidity.The altitude and litter thickness contributed the maximum to the species composition and distribution pattern based on canonicalcorrespondence analysis.