The Human‐Imprinted Regional Species Pool: Functional Trait Patterns of Commercial and Established Plants

ABSTRACT Urban plant communities assemble from a regional species pool shaped by both ecological processes and horticultural trade, yet how these two forces jointly structure its functional composition remains poorly understood. We characterized the potential regional species pool of Switzerland by compiling 5295 vascular plant species spanning herbs, shrubs, and trees and comparing established species (wild‐established only), commercial species (horticulturally available only), and overlapping species (both). Using a trait database covering life‐history strategies, morphology, environmental preferences, and human use, we examined functional trait space using principal component analysis and quantified functional richness, dispersion, and originality. We further tested which traits were associated with wild establishment among non‐native species and invasive status among overlapping species using Firth logistic regression. Commercial species were unevenly distributed across growth forms, dominating among trees (67.9%) and shrubs (59.7%) but less represented among herbs (17.9%). Functional differentiation was strongest along an environmental niche axis, with commercial herbs associated with drier conditions and commercial woody species with warmer conditions. Commercial species consistently had the lowest functional richness, dispersion, and originality across all growth forms. Wild establishment was associated with multiple environmental, reproductive, and ecological traits, whereas invasive status was associated with warmer temperature preference and anthropogenic tolerance, although the latter analysis was exploratory. These results indicate that commercial availability creates a functionally selective pool of species that may influence later urban community assembly. By shaping the functional possibilities available before local assembly occurs, horticultural trade may therefore leave an important human imprint on urban biodiversity, with potential downstream consequences for ecosystem functioning and trophic interactions.