Field experiments on seed dispersal by wind in ten umbelliferous species (Apiaceae)

This report presents data from experiments on seed dispersal by wind for ten species of the family Apiaceae. Seed shadows were obtained in the field under natural conditions, using wind speeds between four and ten m/s. The flight of individual seeds was followed by eye, and seed shadows were acquired, with median distances varying from 0.7 to 3.1 m between species. Multiple regression models of wind speed and seed weight on dispersal distance were significant for six out of ten species; wind speed had significant effects in seven cases, but seed weight only once. A good correlation between mean terminal falling velocity of the seeds of a species and median dispersal distance, indicates the promising explanatory power that individual terminal velocity data might have on dispersal distance, together with wind speed and turbulence. The theory that seeds that seem to be adapted to wind dispersal travel much longer distances than seeds that have no adaptation was tested. Flattened and winged seeds were indeed found to be transported further by wind, but not much further. Moreover, the species with wind-adapted seeds were also taller, being an alternative explanation since their seeds experienced higher wind speeds at these greater heights. Furthermore, flattened and winged seeds were disseminated from ripe umbels at lower wind speeds in the laboratory. This means that the observed difference in dispersal distance would have been smaller when species specific thresholds for wind speed were incorporated in the field experiments. We argue therefore, that seed morphology is not always the best predictor in classifying species in groups with distinctly different dispersal ability.