Patterns and drivers of phylogenetic diversity of seed plants along an elevational gradient in the central Himalayas

The how and why of the spatial variation in biodiversity is one of the fundamental topics in biogeography research, but accurate insights require the incorporation of phylogenetic information. Here, to provide a better understanding of the origin and mechanism of biodiversity in montane ecosystems and thus support conservation planning, we explored the elevational patterns of phylogenetic diversity and structure of seed plants in the Gyirong Valley, the longest valley in China's central Himalayas. The observed patterns were related to climatic, historical, geographical, and disturbance-related factors, and the relative contributions of these factors in explaining them were assessed. Our results showed that phylogenetic diversity of seed plants in the central Himalayas were described by a strongly hump-shaped pattern, peaking at 2700 m around. The phylogenetic structure of the plants was characterized by overdispersion at lower elevations and clustering at higher elevations, reflecting the cooperation between interspecies competition and environmental filtering in community assembly. Among the examined environmental factors, climatic factors showed the highest explanatory power, suggesting environmental filtering was largely driven by climatic rather than other factors. In summary, our finding indicating that mild climate at lower elevations presumably encourage phylogenetic differentiation by promoting interspecies competition, whereas increasingly harsh climatic condition with elevation may lead to closer phylogenetic relatedness through environmental filtering. Overall, our findings improve our knowledge about the elevational gradient of biodiversity in the Himalayas, and highlight the need for intensified conservation efforts at middle elevations as well as greater scientific concern regarding the impact of climate change on the biodiversity.