Sediment and seed bank dynamics in river systems of southeastern Australia: implications for vegetation-based river rehabilitation

A riparian seed bank is a reserve of viable seeds and propagules in sediments of a river channel, channel bank and adjacent floodplain. Dispersal of seeds by water is termed hydrochory. Over the last 20 years, geomorphologists and ecologists have recognized the role of vegetation as an important control on the form and stability of river margins. There is now increasing recognition that these two areas of interest should be integrated in order to improve riparian management strategies that enhance the natural recovery mechanisms of river systems. However, our understanding of the dynamics of the riparian seed bank remains poor, particularly in an Australian context. Hydrochoric seeds are subject to the same forces as sediment in a river system. Sediment (and seeds) are sourced, transported and stored at various positions in a catchment. Hence, the mechanisms by which sediment is transported and deposited is a key control on the dispersal and storage mechanisms of seeds in the channel and riparian zone of rivers. In this presentation we will introduce background principles of riparian seedbank science and outline some of our research occurring in Wollombi Brook and Watagan Creek, eastern NSW. Through postdoctoral and PhD research we are designing experiments to: 1) Determine the type, volume, structure and viability of the soil seed bank within different geomorphic units and compare it to seed rain and extant vegetation associations. 2) Determine the relationship between hydrology, geomorphic structure and seedbank dynamics along intact riparian corridors. 3) Develop guidelines for best practice river rehabilitation based on an understanding of sediment transport and storage and seed bank dynamics.