The rapid expansion of road networks is a key driver of reduced connectivity across forested landscapes worldwide. Roads can alter wildlife movement, disrupt ecological processes, and limit the natural pathways that maintain forest resilience in the face of land use and climate change.
Seed dispersal by animals is a key natural process that helps forests regenerate, stay resilient to climate change, and maintain healthy genetic diversity among tree populations. Because many forests rely on mammals to move seeds across habitat boundaries, understanding how roads influence these movements has become increasingly important for conservation planning. Yet guidance remains limited on how different road types and roadside conditions affect animal-mediated seed dispersal.
Craveiro, J., Bugalho, M.N. and Vaz, P.G. 2025. Roads shape seed dispersal by rodents and carnivores at forest edges. Journal of Applied Ecology 62(11): 3040-3054. DOI: 10.1111/1365-2664.70174
To address this gap, new research examined how road characteristics and their position in the landscape influence seed dispersal by small mammals and carnivores in Mediterranean oak woodlands of southern Portugal. The study compared paved and unpaved roads situated either at forest edges or within continuous forest.
Field experiments tracked small-mammal dispersal by placing 1,440 labeled holm oak acorns inside small protective cages along roads and in paired roadless control areas, then monitoring movements for several months. Carnivore-mediated dispersal was assessed by embedding seed mimics in dried fruits, using camera traps to identify consumers, and conducting systematic scat surveys across a 1.2 km radius to locate dispersed seeds and identify road crossings.
Small mammals dispersed more than half of the experimental seeds, generally moving them short distances of about 5 meters. Seed movement was greater along road verges than in roadless forest, and farthest at forest edges where suitable caching sites were more limited.
Roads acted as partial barriers, particularly when paved, since road crossings by small mammals were rare. Most small-mammal dispersal occurred parallel to the road, indicating that roadside vegetation strongly influences movement pathways. Shrub cover increased both the number of seeds moved and dispersal distance, suggesting that vegetation structure along verges plays an important role in forest regeneration processes.
Carnivores dispersed fewer seeds overall but moved them substantially farther, with average dispersal distances of around 460 meters. They crossed roads with seeds far more frequently than small mammals, especially on unpaved roads and in forest interior contexts.
Dispersal was predominantly perpendicular to the road and directed into forested areas, making carnivores important agents of long-distance connectivity between habitat patches. Fewer dispersal events occurred in areas with multiple water patches, likely because carnivores shifted movement toward riparian corridors rather than roadsides.
The results show that roads can simultaneously hinder and facilitate seed dispersal, influencing forest connectivity at both local and landscape scales. Paved roads tend to inhibit movement, while unpaved roads can function as ecological corridors that support long-distance seed flow.
Strategic roadside vegetation management offers an opportunity to enhance natural regeneration. Maintaining moderate shrub cover along paved roads can support small-mammal movement while balancing safety and maintenance needs. Unpaved verges provide valuable conduits for carnivore movement and should be managed to sustain habitat continuity between forest fragments. Integrating these insights into road planning and vegetation management can improve forest connectivity and resilience amid ongoing habitat fragmentation.
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