Changes of herbaceous diversity along altitude gradients and community stability in the middle reaches of the Yarlung Zangbo River in China

Located in western and southwestern China, the Qinghai-Tibet Plateau is an important ecological security barrier area in China with a variety of vegetation types, and measuring plant population diversity is challenging due to its high altitude.In this paper, the herb communities in the middle reaches of the Yarlung Zangbo River on the Tibetan Plateau were investigated, and the variation of their diversity with altitude gradient, the similarity and stability of community structure were analyzed,The Alpha diversity index and Beta diversity index of species and the similarity and stability index of community were measured.The results show that:(1)In 7 elevations 7 sampling sites 70 quadrates with a total area of 700m 2 , 39 species of herbs were recorded, belonging to 20 families and 33 genera. Poaceae plants occupy a large proportion in all elevations, and are the first dominant species of herbs, followed by Asteraceae .(2)The highest species abundance and number of herbaceous species were reached in the altitude range of 3,600-3,800m, and the most suitable climate and geographical conditions for the survival of herbaceous communities were reached in the altitude range.(3)According to the Jaccard similarity index among the 7 altitude gradients, the community similarity was high when the altitude was below 3600m, while the community similarity was dissimilar when the altitude was above 3600m.(4)From the perspective of community stability index and diversity index, there was no direct correlation between plant community diversity and community stability.