Seed rain as a propagule source for restoration of semi-arid floodplain old fields

Aims

Revegetation of the world's abandoned agricultural land (old fields) is vital to promote biodiversity and restore ecosystem services. Natural regeneration, whereby vegetation regrows on its own via the propagules already within the landscape, is a cost-effective restoration approach for old fields. It is vital that we understand how different seed sources contribute to the regenerative capacity of old fields to make informed management decisions. Little is known about seed rain as a propagule source for restoration within semi-arid floodplains of eastern Australia.

Location

Within this study, we examined seed rain and extant vegetation in old fields and paired remnant sites across four regions in the northern Murray–Darling Basin, eastern Australia.

Methods

Seed rain was surveyed using seed traps that were then subjected to a seedling emergence experiment.

Results

Minimal differences in seed rain composition, species richness, abundance, and plant functional groups were observed between old-field and remnant sites, indicating similarities in seed dispersal within both land use histories. Larger distances to remnant patches and mean annual rainfall were found to drive the composition of old field's seed rain. The study found few emerged Eucalyptus seedlings despite seed traps being placed during peak seed release periods, which may be due to poor tree conditions from drought, interference with seed traps and the episodic germination requirements of Eucalyptus coolabah.

Conclusions

This study demonstrates that seed rain can contribute to the natural regeneration of understorey vegetation, with low abundances of exotic species, unlike other seed bank types. However, seed rain composition resembled little of the extant vegetation, suggesting a species pool facing barriers to germination and establishment, but likely linked to bet-hedging strategies. Moving forward to promote natural regeneration via seed rain in old fields, protecting existing patches of vegetation within the landscape is vital to enable biotic connectivity.