Habitat-specific dispersal:: environmental effects on the mechanisms and patterns of seed movement in a grassland herb Rhinanthus minor

Little is known about how patterns and mechanisms of seed dispersal vary among different habitats. To address this we studied Rhinanthus minor, a grassland annual herb, in four environments: early or late hay cutting, grazing by sheep, and no management. Comprehensive measures were made of dispersal, by intensive seed trapping up to 25 m from source plants and in four directions. We found large differences in dispersal among the environments in terms of curve shape, maximum distance and directionality. Dispersal was shortest under grazing (maximum distance 0.9 m) and furthest under the early cut (19.1 m). Dispersal differences reflect the mechanisms of dispersal in each environment. Dispersal was by wind under no management, and by the mowing machinery under an early cut, whereas a late cut produced a combination of dispersal by. wind and the machinery. Grazing hindered dispersal, through trampling of plants., Additional measures of seed mass supported the hypothesis of a negative seed size vs dispersal distance relationship and suggested its generality across a range of environments. Understanding the variation in dispersal patterns among environments may allow increased realism of spatial models.