Diversity and conservation of higher plants in Northwest Yunnan-Southeast Tibet

Located on the southern margin of the Qinghai-Tibet Plateau, the Northwest Yunnan-Southeast Tibet (NYST) is a biodiversity hotspot. However, plant diversity in the region faces enormous threats, including forest fragmentation and overexploitation of natural resources. Here, we updated the catalogue of higher plants in NYST by integrating various data sources and referring to the newest results of molecular systematics and taxonomy. Combining phylogenetic approaches and a spatial analysis of forest landscape fragmentation, we assessed spatial variations in taxonomic richness and phylogenetic diversity, and identified potential geographic units for conservation gaps. NYST harbours nearly one-third of China's higher plant species, of which ∼60% of the species listed as threatened are endemic. Among the genera, the highest number of endemic and threatened species belong to Rhododendron. The largest increase in the number of threatened species was observed in the Orchidaceae over the last 15 years. Seed plant taxonomic richness and phylogenetic diversity were significantly positively correlated at both the species and genus levels. Counties with large mountains are hotspots of phylogenetic diversity as well as total, endemic, and threatened species richness. The pattern of diversity of higher plants in the study area is likely related to the Himalayan-Tibetan Plateau uplift. The western part of Yulong County and the central to southern parts of Shangri-La County are conservation gaps in this area. In-depth local field surveys of plant diversity are needed, especially in those counties where there is large disparity between the number of species present and collected specimens (e.g., Yulong County). This study provides data and a theoretical basis for the study and conservation of NYST plant diversity.