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

This report presents data from experiments on seed dispersal by wind for te n species of the family Apiaceae. Seed shadows were obtained in the field u nder natural conditions, using wind speeds between four and ten m/s. The fl ight of individual seeds was followed by eye, and seed shadows were acquire d, with median distances varying from 0.7 to 3.1 m between species. Multipl e regression models of wind speed and seed weight on dispersal distance wer e significant for six out of ten species; wind speed had significant effect s in seven cases, but seed weight only once. A good correlation between mea n terminal falling velocity of the seeds of a species and median dispersal distance, indicates the promising explanatory power that individual termina l velocity data might have on dispersal distance, together with wind speed and turbulence. The theory that seeds that seem to be adapted to wind dispe rsal travel much longer distances than seeds that have no adaptation was te sted. Flattened and winged seeds were indeed found to be transported furthe r by wind, but not much further. Moreover, the species with wind-adapted se eds were also taller, being an alternative explanation since their seeds ex perienced higher wind speeds at these greater heights. Furthermore, flatten ed and winged seeds were disseminated from ripe umbels at lower wind speeds in the laboratory. This means that the observed difference in dispersal di stance would have been smaller when species specific thresholds for wind sp eed were incorporated in the field experiments. We argue therefore, that se ed morphology is not always the best predictor in classifying species in gr oups with distinctly different dispersal ability.