Primary and secondary dispersal of grass species in the Patagonian steppe

MARTÍN AGUIAR; RUY PEREA; SEBASTIÁN AGUIAR

Montpellier

Workshop; Plant Dispersal and Migration workshop; 2001

Dispersal distance of seeds is the result of two processes - primary and secondary dispersal - controlled by seed morphology, surface roughness, and wind velocity. We studied separately the two process by following individual seeds from two grass species Bromus pictus and Poa ligularis during five minutes. Seed dispersal was studied along a grazing intensity to capture the effects of land-use on surface roughness. Dispersal distance was relatively short (less than 1 m) and was affected species characteristics and grazing condition. To evaluate what happens after the first minutes we studied seed permanence in different microsites. After 80 days seeds located in bare soil and close to pebbles disappeared, whereas around 80 % of the seeds located in grass, shrub or litter covered patches remained in place. Based on our results we propose that dispersal distance in low and sparse vegetation of arid and semiarid ecosystem may short. Height of vegetation constrain distance on primary dispersal, whereas sparse vegetation promotes dispersal distance in secondary dispersal. Land-use, such as overgrazing may increase dispersal distance by reducing surface roughness.