Figure 1.
The car remained within the driving lane, making this the section most directly impacted by the passing vehicle. The adjoining sections (left and right) were not driven over, but would have been strongly affected by the vehicle's airflow. Seed settlement is considered to occur in the verge, which provides the most immediate establishment opportunity for seeds. The opposite lane represents the area beyond the midpoint of the lane, where, on a real road, the seed would be in the path of oncoming traffic.
Figure 2.
Probability distributions of seeds along the study road after 80 vehicle passes.
(A) Ailanthus altissima (B) Clematis vitalba, (C) Ambrosia artemisiifolia and (D) Brassica napus. Filled circles represent the mean (±95% CI) probabilities of 10 replicates. The grey lines show the fitted dispersal functions. Open triangles show mean probabilities for seeds to reach the road verge at that distance along the line of travel. The y-axis is on a log scale and 0.0001 was added to all probabilities to show zero values. Note that this is not a total dispersal kernel but solely shows secondary dispersal by car's airflow.
Table 1.
Characteristics of the study species.
Figure 3.
Effect of the number of vehicle passes on the shape of the fitted dispersal kernel (Lognormal function).
(A) Ailanthus altissima, (B) Clematis vitalba, (C) Ambrosia artemisiifolia, and (D) Brassica napus. The y-axis is on a log scale and 0.0001 was added to all probabilities to show zero values. Inset tables show parameter estimates (a = scale parameter, b = shape parameter) for the different numbers of vehicle passes.
Table 2.
Dispersal distances for the study species after different numbers of vehicle passes.
Table 3.
Parameter estimates and AIC for different dispersal functions.
Figure 4.
Lateral movement of seeds of Ailanthus altissima in relation to the number of vehicle passes.
(A) Mean probabilities of seed deposition of Ailanthus altissima in the parallel road sections in relation to the number of vehicle passes. (B) Proportion (±95% CI) of seeds of Ailanthus altissima accumulating at the verge in relation to the number of vehicle passes. At the start of experiment seeds were laid out only on the driving lane.
Figure 5.
Influence of the starting section on parallel and lateral movement of seeds by a passing car.
Dispersal patterns of Ailanthus altissima seeds after one vehicle pass for seeds initially placed in the verge (left panel), the left side (second panel from left) the driving lane (centre panel), the right side (second panel from right) and the opposite lane (right panel). Probabilities of reaching the different sections of the study road are indicated by different grey shading. Probabilities are averaged over 50 replicates.