The dispersal characteristics of the invasive plant Mimulus guttatus and the ecological significance of increased occurrence of high-flow events

1 Increased occurrence of high-flow events as a result of climate change may affect the dispersal success of an invasive plant species Mimulus guttatus and may result in range expansion. Predicted changes in climate point to a continuation of the recent observed trends in increased precipitation and high-flow events in Northern Europe. 2 The study focused on the dispersal characteristics of M. guttatus, and especially the roles of vegetative fragmentation with increasing water velocities, subsequent fragment survival, regeneration and colonization, as well as the buoyancy, survival and germination success of seeds. 3 M. guttatus was found to fragment readily under velocities typical of high flow conditions and even small fragments had high survival, regeneration and colonization capacity. 4 Large numbers of small (< 0.02 mg) seeds are produced; however, seeds have a short buoyancy period so the timing and magnitude of high-flow events is crucial in determining potential dispersal distances. Seeds germinate readily both in water and on sand with an average 33% germination within 9 days. 5 The dual strategy of dispersal by vegetative fragments and seeds, together with the opportunity of dispersing the two types of propagules during different periods of the year, facilitates local dominance by M. guttatus as well as long-distance colonization. As a result, the rate of spread of M. guttatus into inundation communities along rivers is likely to increase with more frequent high-flow events, especially if these coincide with the growing season. Thus, predicting the response of riparian invasive species to environmental change requires not only an understanding of the role of climate in plant demography but also the impact of changes in hydrology on rates of spread