Paved Roads as Ecohydrological Modifiers: Slope-Driven Runoff Is Associated With Roadside Establishment of the Atlantic Halophyte Cochlearia danica in Continental Europe.

Linear transport infrastructures are widely recognised as corridors for plant dispersal; however, their role in modifying local abiotic conditions remains less explored. In this study, we examined whether slope-driven, unidirectional precipitation runoff from paved roads is associated with differences in roadside soil-moisture and local abundance of Cochlearia danica, an Atlantic halophytic species currently spreading into continental Europe. Targeted roadside surveys were conducted in Slovakia, Hungary, Serbia and Romania, complemented by comparative soil-moisture assessments on opposing sides of sloping road sections. Downslope verges receiving concentrated runoff consistently showed higher gravimetric soil-moisture and were associated with larger C. danica populations than upslope verges. Population size showed a positive association with local variation in soil-moisture. Supplementary species distribution modelling based on bioclimatic variables predicted low macroclimatic suitability for the study region, indicating that several recorded roadside populations occur under marginal conditions. In addition to Hungary, C. danica was documented for the first time in Serbia and Romania, with evidence suggesting local establishment of revisited sites. Our results suggest that paved road design may create small-scale ecohydrological asymmetry along road verges, potentially contributing to the establishment of Atlantic halophytes in continental roadside habitats.