Global effects of patch edge on plant species alpha diversity

• Effects of four edge metrics on alpha diversity were identified across three vegetation types. • Edge metrics have greater impact on shrub diversity than other vegetations. • Shape complexity and distance to edge have positive relation with plant diversity. • Edge metrics have more greatly impact on alpha diversity at larger scale. • Plant diversity has greater relation with morphological traits than other traits. Despite extensive global research on edge effects, their generalizable patterns across multiple spatial scales and vegetation types remain unclear. Using 6,188 vegetation plots worldwide, this study investigated how four edge metrics influence plant species alpha diversity, integrating functional trait diversity analysis. Results revealed stronger impacts of edge metrics on shrub diversity and more pronounced effects at larger scales. For all vegetation types, increases in shape complexity (PMSI), edge length, and distance to the edge were significantly associated with rising Shannon-Wiener (H) and Simpson (D) indices. Conversely, species richness declined significantly with increasing edge density (ED), while the Pielou index increased with higher PMSI and ED. Forest diversity indices were more strongly correlated with reproductive and morphological traits, whereas shrub and grassland indices showed stronger links to nutritional and morphological traits. These findings enhance understanding of how edge metrics structure plant diversity in fragmented habitats, providing a basis for predicting biodiversity responses to landscape change.