Dispersal of seeds by vehicles
Human-mediated dispersal is known as an important driver of long-distance dispersal for plants, but underlying mechanisms have rarely been assessed. Road corridors function as routes of secondary dispersal for many plant species, but the extent to which vehicles support this process remains unclear. The dispersal distances and seed deposition of plant species moved over the ground by the slipstream of passing cars have been quantified. Marked seeds of four species were exposed on a section of road and a car was driven along the road at a speed of 48 km/h. The four species used were Ailanthus altissima (Simaroubaceae, EPPO List of IAP), Ambrosia artemisiifolia (Asteraceae, EPPO List of IAP), Brassica nappus (Brassicaceae) and Clematis vitalba (Ranunculaceae) as they have different seed morphology, are common along roads and are spread via vehicle movements. The effect of repeated vehicle passes was quantified by tracking parallel and lateral movement of seeds to the road.
Median distances travelled by seeds along the road were about 8 m for species with wind dispersal morphologies and 1 m for species without such adaptations. Airflow created by the car lifted seeds and resulted in longitudinal dispersal. Single seeds reached a maximum distance of 45 m. The incremental effect of passing vehicles on longitudinal dispersal decreased with increasing number of passes as seeds accumulated at road verges. It can therefore be concluded that dispersal by vehicle airflow facilitates seed movement along roads and the accumulation of seeds in roadside habitats. Dispersal by vehicle airflow can aid the spread of plant species and thus has wide implications for roadside ecology, invasion biology and nature conservation.
Sources
von der Lippe M, Bullock JM, Kowarik I, Knopp T ; Wichmann M (2013) Human-Mediated Dispersal of Seeds by the Airflow of Vehicles. PLoS ONE 8(1): e52733. doi:10.1371/journal.pone.0052733