Relationships between seed bank composition and an invasive plant in a floodplain wetland of the Murray–Darling Basin

Abstract

Seed banks are an important characteristic of wetland plant assemblages, enabling the storage of dormant propagules through wet and dry periods until the next favourable period for growth and reproduction. In this study, we use a seed bank emergence experiment to investigate whether the seed bank of a grassy floodplain wetland located in Australia’s Murray–Darling Basin has been impacted by the invasion of Juncus ingens N.A. Wakef. River regulation and altered flood regimes have encouraged the spread of this species throughout grassy wetland areas, particularly at Barmah Forest, a Ramsar Convention-listed wetland of international significance in Victoria. We particularly focus on changes in the seed bank of an ecologically important, but declining, floodplain grass, Pseudoraphis spinescens (R.Br.) Vickery, and implications for restoration. We found that sites invaded by J. ingens had a higher density of emerged J. ingens plants, a lower density of P. spinescens and a lower overall native species richness. J. ingens-dominated sites were also characterised by a significantly deeper maximum flood depth than P. spinescens-dominated sites. The overall density of P. spinescens plants emerging from the soil was very low in comparison to most other species, and largely restricted to shallow sites where the species was already present. This suggests that restoration efforts may need to focus on encouraging vegetative regrowth from existing grassy swards, rather than expecting recovery from a viable seed bank, and highlights the importance of conserving the remaining P. spinescens patches at Barmah Forest.