Secondary Dispersal Of Willow Seeds: Sailing On Water Into Safe Sites

Abstract

Abstract Willows (Salix spp.) produce many small seeds that are dispersed primarily through the air by winds (anemochory) and sometimes secondarily by flowing water (hydrochory). In this paper I identify another way willow seeds are dispersed – being blown by winds while sailing or floating on the surface of standing water, here termed pleustochory. In experiments, seeds of Salix gooddingii C.R. Ball floated on water for four days and sailed swiftly on the surface of pools when light winds blew, reaching speeds in excess of five meters per minute. Field observations showed that S. gooddingii seeds sailing on water were blown downwind and soon came to rest at the edge of the pool, in their preferred safe sites. This dispersal via pleustochory from unsuitable sites (middle of a pool) into safe sites (edge of pool) is therefore a new example of directed dispersal. Salix gooddingii seed dispersal and seedling densities were studied at a large, remote pool in the Tijuana River Valley, San Diego Co., to examine...