Orientation and speed of wind gusts causing abscission of wind-dispersed seeds influences dispersal distance

Summary: Abscission of seeds in some plant species occurs as a result of strong wind gusts that exert sufficient drag forces to liberate the seed from its parent. This may be an adaptive feature, as release into stronger wind gusts has been shown to lead to greater dispersal distances, which is likely to have evolutionary advantages. We test the hypotheses that (i) seeds released into upward wind gusts will, on average, travel further than those seeds released into wind gusts with horizontal or downward orientations and (ii) that the preferential abscission of seeds into upward wind gusts will result in the dispersal of seeds over greater distances. As a case study, we studied the abscission dynamics of Conyza bonariensis (L.) Cronquist (fleabane), which is an important weed with global distribution. Using abscission data obtained through a series of seed release experiments, we confirm that abscission of seeds in C. bonariensis is most likely to occur during strong and upward wind gusts. We demonstrate that, for a given wind speed, seeds released into upward wind gusts will, on average, travel further than those seeds released into wind gusts with horizontal or downward orientations. We also show that preferential release into upward wind gusts has some influence on the distance travelled, but the strength of this influence is dependent on the correlation between wind orientation and wind speed. For this particular study, the sensitivity of release to the horizontal wind speed seems to have a larger effect on the distance travelled than sensitivity to wind orientation. © 2013 British Ecological Society.