Wind Dispersal Distances in Dimorphic Achenes of Ragwort, Senecio Jacobaea

Abstract

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.

Diaspore heteromorphism in the invasive Bromus tectorum L. (Poaceae): Sterile florets increase dispersal propensity and distance

“…This supports previous evidence that shrubs act as windbreaks and can reduce anemochory (McEvoy and Cox, 1987). Secondary dispersal was highest in disturbed areas and shrublands, i.e.…”

“…These results confirm those of Johnston (2011) and Monty et al (Monty et al, 2013), who found even more important rates of secondary dispersal of B. tectorum in areas with almost no vegetation (reclamation and burned areas, respectively). Research on other species also found an influence of vegetation on ground level dispersal through a decrease in wind speed, changes in wind turbulence and seed entrapment (Chambers, 2000;Marushia and Holt, 2006;McEvoy and Cox, 1987).…”

Espectro e distribuição vertical das estratégias de dispersão de diásporos do componente arbóreo em uma floresta estacional no sul do Brasil

“…Para estas, fatores como a altura da árvore, a velocidade e a direção do vento (Isaac 1930;Horn et al 2001), a topografia e a vegetação adjacentes (Cremer 1965), e a umidade (McEvoy & Cox 1987) influenciariam a dispersão. Aparentemente, grande parte dessas variáveis atua uniformizando o investimento na dispersão em todas as direções e para a maior distância possível.…”

Theoretical contributions to biological control success

“…Finally, the activator-inhibitor framework incorporates environmental disturbance, movement and spatial heterogeneity. This motivated the gathering of detailed information on movement showing that the relative dispersal ability of the host plant (McEvoy and Cox 1987) is much less than that of the natural enemy species [the cinnabar moth T. jacobaeae, the ragwort flea beetle L. jacobaeae, and the ragwort seed head fly Botanophila seneciella (Meade, 1892)] under field conditions (Harrison et al 1995;Rudd and McEvoy 1996). Thus, natural enemies can easily overtake and suppress a weed population spreading autonomously.…”