Multiple pathways in diaspore dispersal, exemplified by studies of Noogoora Burr (Xanthium occidentale Bertol., Compositae)

LIDDLE, M. J. & ELGAR, M. A., 1984. Multiple pathways in diaspore dispersal, exemplified by studies of Noogoora Burr (Xanthium occidmtale Bertol., Compositae). Some of the ways in which the burrs are dispersed and some of the factors that may cause changes between the different dispersal pathways were examined. Populations of burrs were marked on the plants in an ungrazed paddock, a paddock grazed by horses, and a paddock grazed by sheep. Eleven percent of the marked populations were recovered from the hair of horses and 26% from the sheeps' wool. A single flood removed 80% of one population. Burrs moved a mean distance of 30 cm on paths used by horses and 18% were buried in the path soil. Burrs were placed in animals' hair by hand. After 16 days, sheep retained 76% of the burrs in their wool, while only 2% remained in the hair of horses and cattle. An experiment showed that burrs may be catapulted up to a distance of 3.3 m from the plants. A model is presented which outlines the alternative or sequential pathways that may be followed by the burrs. Occasional events, such as flooding and presence or absence of stock, were the main causes of changes between pathways. In the model, these dispersal mechanisms are considered as release-phase and substrate-phase processes. Each process derives its energy from different sources and may be modified by inputs of energy from other sources.