Seeds of change: the role of seedbanks in plant invasion of heavily disturbed dryland riverine habitats in the northern Murray-Darling Basin

Seedbanks are an important reservoir of plant diversity from which plants are able to regenerate, particularly in dynamic, disturbance-driven landscapes characterised by unpredictable environmental variation. Understanding the composition of seedbanks and their role in extant vegetation dynamics provides insights into past and future vegetation change, including the potential for plant invasions under different scenarios. In ecosystems subject to anthropogenic disturbance, however, seedbank dynamics remain poorly understood, especially in relation to their contribution to plant invasion. Here, I investigate the composition of soil and litter seedbanks across riverine habitats (instream, riparian, and floodplain) in the heavily modified agricultural landscapes of the northern Murray–Darling Basin, eastern Australia. Using germination trials, I examined spatial variation in native and non-native seedbank assemblages and explored likely environmental drivers of seedbank composition as well as similarity to the extant vegetation. It was found that germinable seedbanks comprise a wide range of native growth forms as well as a diverse assemblage of opportunistic plant invaders. Non-native seedbank assemblages were associated with land use and hydrological variation, reflecting the roles of disturbance, stochasticity, and opportunism in shaping invasion pathways. Floodplain habitats harboured seeds of the greatest number of non-native species. Numerous native and non-native species detected in seedbanks were absent from corresponding extant vegetation assemblages, suggesting the potential for extant vegetation shifts under changing environmental conditions, including further invasions.