Primary and secondary seed dispersal by wind and water in Spergularia salina

Abstract

The patterns of repositioning by wind and water following their initial dispersal from the parent plant, of winged and unwinged seeds of the heteromorphic halophyte Spergularia salina were Investigated experimentally in both dense vegetation and bare ground under field conditions in a sea shore meadow in eastern Sweden Seeds were placed in situ in the field, and after four days with wind as the sole dispersing agency, 19% of the seeds were repositioned After another 11 days, during which both wind and water acted as dispersing agencies, all seeds of both types had either become repositioned and were still visible (1/3 of the seeds), had penetrated into the ground at the point of release or after dispersal (1/3), or were not recovered (1/3) The probability to become lifted secondarily by water was similar in both seed types Of those seeds repositioned and recovered on the ground, more of the winged type had been transported any distance horizontally than the unwinged type The seed dispersal curve was strongly skewed to the left, and the winged seed type was transported slightly further than the unwinged type, both during primary and secondary dispersal All seeds were transported further when placed on bare soil than when placed in dense vegetation Vertical transportation was quicker in dense vegetation, and unwinged seeds disappeared more quickly into the ground In dense vegetation, unwinged seeds were more frequently encountered in the seed bank than winged seeds, whereas in the absence of vegetation cover, seeds of both types recovered in the soil were found in equal shares