Wind Dispersal Distances in Dimorphic Achenes of Ragwort, Senecio Jacobaea.

A mark-recapture study of wind-dispersed achenes of Senecio jacobaeo conducted in western Oregon showed that the proportion of achenes dispersing a given distance varied significantly with changes in site (inland vs. coastal), surroundings (mown vs. unmown), height of release (0-50, 50-100, 100-150, 150-200 cm), time of release (early vs late in the season), direction of dispersal, and achene type (disk vs. ray achenes). Influences of height of release, direction, achene type, and time of release were strongly conditioned by site and surroundings. The majority of achenes dispersed very short distances. Of 53 301 achenes falling in the recapture area, 31% travelled only 1 m, 89% travelled 5 m or less, and none were collected > 14 m from the source. Thus, while it is theoretically possible for these wind-dispersed achenes to travel long distances, actual dispersal distances are short due to local conditions of humidity, wind, and vegetation structure.