Floatability and a semiempirical model for resuspension thresholds of hydrochorous seeds

Floatability and incipient motion of seeds are the key indicators in primary and secondary dispersal during hydrochory, respectively. Floatability could prolong the time for seeds' survival in water and thereby extend the distance of primary dispersal. Seeds that were deposited but did not germinate may be resuspended and transported by currents farther until permanently stranded. This study aimed to describe and predict the dispersal patterns and movements of seeds with these 2 indicators under static and dynamic water conditions that correspond to the 2 aforementioned dispersal phases. The physical properties and hydrodynamic characteristics of seeds from 3 angiosperm species were used to study the floatability and resuspension thresholds of hydrochorous seeds. Floatability quantified by the number of seeds remaining buoyant varies among the 3 species, implicating their differing capabilities of primary dispersal. Resuspension thresholds of settled seeds were quantified by critical currents (shear velocities) that move seeds at rest on the bed sediment. On the basis of a model of nonuniform sand and collected experimental data, we proposed a model suitable for incipient motion of seeds from the bed. This model can be applied in the evaluation of secondary dispersal potential under different flow conditions. The preliminary research on the movements of seeds in water helps elucidate and determine species distribution and establishment. These factors are important in dispersal ecology.