FRUIT ABSCISSION IN ACER-SACCHARINUM WITH REFERENCE TO SEED DISPERSAL

Winged fruits and seeds travel approximately twice as far as predicted by micrometeorological models of seed dispersal by the wind. We hypothesize that seeds preferentially abscise at higher velocities because the motive force for abscission is drag (proportional to the square of the wind velocity). A 3-year study of fruit abscission in Acer saccharinum L., supplemented by experimental studies, demonstrates that for this species (i) separation layers develop rapidly when relative humidity is low (the early afternoon in a typical diurnal relative humidity cycle), and (ii) the exponents in power law equations relating abscission rate to wind speed are somewhat higher than the expected value of 2.O. Consequently, micrometeorological models of dispersal must be modified to account for the nonrandom nature of abscission.