Roads shape seed dispersal by rodents and carnivores at forest edges

Abstract

The influence of road networks on seed dispersal remains poorly understood. We conducted a field experiment in Mediterranean oak woodlands of southern Portugal to assess how road type (paved vs. unpaved) and road-forest context (edge vs. non-edge) shape seed dispersal by rodents and carnivores. Using labeled acorns and seed mimics, we tracked dispersal distances, number of dispersals, road crossings, and dispersal directions. Rodents dispersed seeds farther in forest edges and along paved roadsides, predominantly moving them parallel to roads, but rarely across--although crossings were more frequent on unpaved roads. In contrast, carnivores mediated long-distance dispersal, primarily perpendicular to roads, and although seed road crossings were rare, carnivore-dispersed seeds crossed roads--especially unpaved ones--nine times more frequently than rodent-dispersed seeds. Shrub cover increased rodent-mediated dispersal events, heavier acorns traveled farther, and water patches decreased carnivore-mediated dispersal events near roads. These findings highlight the dual role of roads as barriers and of roadsides as corridors for seed dispersal, with implications for forest regeneration and landscape connectivity. Roadside management should prioritize moderate shrub cover along paved roads to support rodent dispersal while balancing ecological benefits with potential trade-offs. Unpaved roads, in turn, should be managed as functional corridors for carnivores, enhancing connectivity between fragmented forests. By integrating species-specific dispersal processes into road planning, landscapes can be designed to minimize road barrier effects while promoting natural regeneration in human-modified forests.