Dandelion seed dispersal: The horizontal wind speed does not matter for long-distance dispersal - it is updraft!

Long-distance dispersal of seeds (LDD) surely affects most ecological and evolutionary processes related to plant species. Hence, numerous attempts to quantify LDD have been made and, especially for wind dispersal, several simulation models have been developed. However, the mechanisms promoting LDD by wind still remain ambiguous and the effects of different weather conditions on LDD, although recognized as important, have only rarely been investigated. Here we examine the influence of wind speed and updrafts on dispersal of dandelion (Taraxacum officinale agg.), a typical wind-dispersed herb of open habitats. We used PAPPUS, a weather-sensitive mechanistic simulation model of wind dispersal, which considers frequency distribution of weather conditions during the period the simulation refers to. A simulation for the 4-month shedding period of dandelion shows that high wind speed does not promote LDD. In contrast, vertical-turbulence, especially convective updrafts, are of overwhelming importance. Mainly caused by updrafts, in the simulations more than 0.05% of dandelion seeds were dispersed beyond 100m, a distance commonly used to define LDD. We conclude that long-distance dispersal of seeds of herbaceous species with falling velocities <0.5-1.0 ms(-1) is mainly caused by convective updrafts.