Centuries of periodic inundation have shaped billabongs across the Murray-Darling Basin, and the plant communities they support. However, climate change and river regulation by humans have changed when and how often these systems are filled by overbank flows.
Some billabongs sit low enough on the floodplain that they fill in most years during freshes and small floods. Others are only connected during much larger flows, and may not fill for years at a time. These differences are likely to shape the delivery of seeds and sediment, the cues that trigger germination, and the plant communities that establish across the billabong profile, but how much they do so is not well described. Longer gaps between floods can favor terrestrial species, which are dominated by exotics and may outcompete native wetland plants. Drying is a normal part of how billabongs work, and not every wetland is meant to hold water every year. Seed banks are a major source of new plants when billabongs refill, but seeds do not stay viable forever, so billabongs that go many years between floods may hold a different set of species.
This research compares vegetation among billabongs of similar form and elevation on the lower Goulburn and Ovens River floodplains. The regulated Goulburn and unregulated Ovens differ in how frequently overbank flows occur. Field surveys will record species composition, cover, and structure across an elevation inundation gradient within each site, and soil cores from the same gradient will be germinated to describe the seed bank.
Surveys will inform the extent to which inundation frequency shapes plant communities and seed banks in billabongs, and whether seed banks retain the capacity to regenerate vegetation when water returns. These findings can help catchment managers identify which billabongs are best placed to respond to environmental watering under increasing climatic pressure.