Multidimensional biodiversity indicators reveal hydrothermal filtering and restoration priorities along an altitude gradient in the Lancang river dry-hot valley

Dry-hot valleys are climate-sensitive mountain systems where biodiversity monitoring must connect community responses with practical restoration priorities. We tested whether a multidimensional indicator suite integrating taxonomic, functional and phylogenetic attributes can diagnose plant community assembly along an altitude gradient in the upper Lancang River dry-hot valley. Vascular plants were surveyed in 16 plots across five altitude bands (2100–2700 m) during the 2024 growing season. We quantified community-weighted means of nine plant traits, four functional diversity indices (FRic, FEve, FDis and Rao's Q), and three phylogenetic metrics (PD, NRI and NTI), and related them to hydrothermal and edaphic variables using Mantel tests and redundancy analysis. Species richness and PD peaked at mid altitude, whereas low- and high-altitude communities had positive NRI and NTI values, indicating stronger environmental filtering under hot-dry and cold constraints. Functional responses were dimension-specific: FRic and Rao's Q declined with altitude, FEve peaked near the transition belt, and FDis increased in the upper belt. Community-weighted traits shifted from drought-conservative syndromes at low altitude to more acquisitive strategies at mid altitude and cold-associated conservative syndromes at high altitude. Mean annual precipitation and soil water content were the strongest correlates across indicator dimensions, while salinity and soil nutrients acted as secondary filters. These results show that combining phylogenetic structure, functional diversity and community-weighted traits provides a practical indicator suite for dry-hot valley monitoring, identifies altitude extremes as priority zones for conservation and restoration, and highlights precipitation and plot-scale soil moisture as early-warning variables under climate change.