THE ROLE OF ABSCISSION IN LONG-DISTANCE SEED DISPERSAL BY THE WIND

It has become clear that long-distance seed dispersal plays a crucial role in plant metapopulation persistence and response to rapid climate change. Recent studies of the role of convective vs. shear-generated updrafts in prompting long-distance dispersal using Taraxacum officinale as an example, suggest that (1) the probability of abscission is independent of horizontal speed and thus (2) shear-induced vertical turbulence is low, and so by default the bulk of updrafts must be due to convection, especially in open habitats such as grasslands. In this paper, I directly test the first hypothesis, and indirectly test the second via a modeling exercise. Employing shorter averaging times than used previously, it is shown that abscission in T. officinale is controlled by horizontal wind speed. Indeed, it is related to the square of the wind speed, as might be expected if drag is the motive force. I also show that this augmentation of wind speed by the abscission bias should sufficiently increase the shear-induced turbulence so that shear rivals convection as a source of updrafts in open habitats. In conclusion, long-distance dispersal by wind will not be successfully modeled until we couple the abscission and subsequent dispersal processes.

[1]  Michael L. Cain,et al.  Methods for estimating long-distance dispersal , 2003 .

[2]  Simon A. Levin,et al.  A Theoretical Framework for Data Analysis of Wind Dispersal of Seeds and Pollen , 1989 .

[3]  Michael L. Cain,et al.  ARE LONG‐DISTANCE DISPERSAL EVENTS IN PLANTS USUALLY CAUSED BY NONSTANDARD MEANS OF DISPERSAL? , 2003 .

[4]  Gabriel G. Katul,et al.  DETERMINANTS OF LONG-DISTANCE SEED DISPERSAL BY WIND IN GRASSLANDS , 2004 .

[5]  S. Levin,et al.  The Ecology and Evolution of Seed Dispersal: A Theoretical Perspective , 2003 .

[6]  Peter Poschlod,et al.  Dandelion Seed Dispersal: The Horizontal Wind Speed Does Not Matter for Long‐Distance Dispersal ‐ it is Updraft! , 2003 .

[7]  D. Greene,et al.  Fruit abscission in Acer saccharinum with reference to seed dispersal , 1992 .

[8]  D. Greene,et al.  LONG-DISTANCE WIND DISPERSAL OF TREE SEEDS , 1995 .

[9]  O. Tackenberg.  Modeling long‐distance dispersal of plant diaspores by wind , 2003 .

[10]  P. Schippers,et al.  Release thresholds strongly determine the range of seed dispersal by wind , 2005 .

[11]  Ran Nathan,et al.  Spatiotemporal variation in seed dispersal and recruitment near and far from Pinus halepensis trees. , 2000 .

[12]  T. Sharik,et al.  Seed dispersal of the endangered virginia round-leaf birch (Betula uber) , 1983 .

[13]  D. Greene,et al.  Wind Dispersal of Seeds from a Forest Into a Clearing , 1995 .

[14]  S. Levin,et al.  Mechanisms of long-distance dispersal of seeds by wind , 2002, Nature.

[15]  Ran Nathan,et al.  FIELD VALIDATION AND SENSITIVITY ANALYSIS OF A MECHANISTIC MODEL FOR TREE SEED DISPERSAL BY WIND , 2001 .

[16]  David M Richardson,et al.  Predicting Plant Migration Rates in a Changing World: The Role of Long‐Distance Dispersal , 1999, The American Naturalist.

[17]  R. Nathan,et al.  Long-distance dispersal of tree seeds by wind , 2001, Ecological Research.