The dispersal of winged fruits and seeds differing in autorotative behaviour

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Abstract
The application of micrometeorological models of heavy particle dispersal to winged diaspores (samaras) requires that the diaspores maintain stable flight and that descent velocity is constant with respect to vertical air motion. Others have argued that these assumptions may be invalid for autorotating samaras and that bilaterally symmetric samaras will disperse farther than asymmetric samaras in conditions of large horizontal wind velocities (and (or) high turbulence) because the asymmetric morphology is inherently less stable in flight. Therefore, application of these models may not be appropriate for asymmetric samaras. Experimental and natural releases of asymmetric and symmetric samaras reported here indicate that the two samara morphologies respond similarly to a given flow regime. Thus, in modelling dispersal, the autorotation of the samaras can be ignored, and the samaras can be regarded as heavy particles descending at a constant rate from source to deposition site. Key words: winged seeds, descent velocity, dispersal, Fraxinus americana, Acer negundo, micrometeorological dispersal models.

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