Abstract
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. In this paper we quantify dispersal distances and seed deposition of plant species moved over the ground by the slipstream of passing cars. We exposed marked seeds of four species on a section of road and drove a car along the road at a speed of 48 km/h. By tracking seeds we quantified movement parallel as well as lateral to the road, resulting dispersal kernels, and the effect of repeated vehicle passes. Median distances travelled by seeds along the road were about eight meters for species with wind dispersal morphologies and one meter for species without such adaptations. Airflow created by the car lifted seeds and resulted in longitudinal dispersal. Single seeds reached our maximum measuring distance of 45 m and for some species exceeded distances under primary dispersal. Mathematical models were fit to dispersal kernels. The incremental effect of passing vehicles on longitudinal dispersal decreased with increasing number of passes as seeds accumulated at road verges. We conclude that dispersal by vehicle airflow facilitates seed movement along roads and 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.
Highlights
Human-mediated dispersal (HMD) is a driver of long-range spread of plant species and is increasingly gaining attention in dispersal [1] and invasion ecology [2,3]
The results indicate that HMD may follow well defined mechanisms and that dispersal distances can far exceed primary dispersal vectors
Three of our study species commonly occur in the study area but to avoid any risk of establishment of the fourth species, we applied a microwave treatment to the seeds of Ambrosia artemisiifolia to prevent any seeds lost from the experimental site from germinating
Summary
Human-mediated dispersal (HMD) is a driver of long-range spread of plant species and is increasingly gaining attention in dispersal [1] and invasion ecology [2,3]. Roadsides are relevant in terms of HMD as some invasive species expand their ranges rapidly along road networks [4,5]. Several studies have demonstrated that the density of human transportation corridors [6,7] or human use of roads [8] are related to the frequency or spread rate of non-native plants. Several studies have demonstrated potential dispersal through attachment to vehicles by finding seeds of many species in samples of mud from the surface of vehicles [9,10,11,12,13]. The role of slipstreams and air turbulence caused by passing vehicles [18] has been suggested to be important in the spread of roadside plant populations [17] but this process has not yet been studied
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