SEED DISPERSAL CAPACITY OF 6 PERENNIAL GRASSLAND SPECIES MEASURED IN A WIND-TUNNEL AT VARYING WIND-SPEED AND HEIGHT

The dispersal capacity of six perennial grassland species with differe nt seed aerodynamic attributes was assessed in a wind tunnel. The sele cted species have difficulty in recolonizing restored ecosystems becau se of a poor dispersal of seeds. The variation in dispersal distances of seeds within and between species was assessed by releasing seeds at varying wind speeds and release heights, and expressed as 1st percent ile, mode, and 99th percentile values. Dispersal distances of long-ran ge dispersed seeds (99th percentile values) increased exponentially wi th wind speed. At wind speeds of 14 m/s, predicted maximum distances a re 10-15 m for small and relatively heavy spherical seeds and 20-30 m for large and relatively light cylindrical or disk-like seeds. In the study area, wind gusts >10 m/s at plant height occur at least annually , and plants of the selected species live up to several decades. This suggests a great potential for long-range dispersal during the lifetim e of a plant. Plants may gain wider dispersal of seeds by increasing t he release height (e.g., taller infructescences) and by requiring stro nger winds to release seeds (e.g., dispersal in autumn and winter).