A Model of Wind Dispersal of Winged or Plumed Seeds

Abstract

We derived a micrometeorological model for the dispersal of winged or plumed seeds from a point source. The model is based on six measurable parameters: mean release height, mean and standard deviation of the terminal velocities of seeds, standard deviation of vertical wind velocities, and the mean and standard deviation of the natural logarithms of horizontal wind velocities. Predictions of the model include (1) the distribution of the dispersal curve (defined as numbers vs. distance from source) is right skewed; (2) the median and long—range dispersal distances need not be well correlated; and (3) increased variance in flight trajectories for a seed population will place the mode of the dispersal curve closer to the source. Empirical tests of the model showed that it adequately characterizes the observed dispersal curves for experimental releases. It is shown that a simple ballistic provides a good estimate of the median dispersal distance (and mean distance if the skew of the dispersal curve is slight) for experimental releases. Tests of the model using natural releases from isolated trees indicated that winged seeds do not detach from the parent randomly with respect to horizontal wind velocity. The need to understand the relationship between the probability of detachment and the frequency distribution of horizontal wind velocities is stressed.