Canopy Plants Safeguard the Taxonomic and Phylogenetic Diversity of Recruiting Plants Worldwide.

Plant recruitment-the transition from seed dispersal to seedling establishment-is a vulnerable stage strongly shaped by canopy plants, which modify microclimates, soils, and biotic interactions relative to open ground. Using a global database covering 142 communities across ten terrestrial biomes, we examined canopy effects on taxonomic and phylogenetic diversity at global and local scales, quantified with Hill numbers (q = 0, 1, 2) to weight rare, common, and dominant species. Globally, canopy microsites hosted five times more exclusive species and over three times more evolutionary history than open ground. Locally, canopies buffered aridity's negative effects, sustaining higher diversity. For q = 1, open ground had higher diversity under low aridity, but under dry conditions canopies promoted rare, stress-sensitive species alongside dominants. These patterns show that canopy plants act as microrefugia, preserving both species richness and evolutionary history, highlighting their critical role as guardians of plant diversity under increasing climatic aridity.