Schooler, S.H., Cook, T., Prichard, G. & Yeates, A.G. (In press).
Disturbance-mediated competition: the interacting roles of inundation regime and mechanical and herbicidal control in determining native and invasive plant abundance.
Disturbance can be driven by either human activity (directly or indirectly) or natural processes and can have different effects on each species in a plant assemblage. We looked at the relationship between the exotic plant alligator weed and two pasture grasses, one native (couch) and one exotic (kikuyu), under the influence of different disturbances over a two year period. Disturbances included a natural gradient in inundation duration, from short to long inundation time, and two human driven disturbances, mowing and herbicide exposure, where herbicide was selective and did not influence the grass species. The two human driven disturbances were looked at separately and in combination with each other and were repeated along the natural disturbance gradient. Alligator weed did better in areas of long inundation duration whereas kikuyu did better in less disturbed areas and couch occurred at low levels along the gradient. In areas of herbicide use alligator weed declined by 97.5%, kikuyu remained the same and couch increased in areas of high inundation disturbance but not in low inundation disturbance areas. Mowing alone did not affect the amount any of the three species occurred in any areas along the inundation gradient. We concluded that human driven and natural disturbance act together to shape the plant assemblage and weed removal should focus on areas which will have the greatest benefit to desired species, in this case areas of higher inundation disturbance where the native plant grows without the influence of the exotic grass.