Regenerative capacity of old-fields on semi-arid floodplains in the northern Murray-Darling basin

Revegetating abandoned agricultural lands is vital to restoring critical ecological functions and services. Natural regeneration, whereby vegetation regrows via the seeds already present within the landscape, has shown to be an effective approach to restoring large agricultural areas, although more research is required to understand the regenerative capacity of the various seed sources. Here, we investigate the regenerative capacity of old-fields of semi-arid floodplains of eastern Australia in a year-long seedling emergence experiment. We examined the germinable seed banks from three potential propagule sources (soil, leaf litter, and animal scats) collected across 24 field sites, comprising 12 old-fields and 12 adjacent remnant vegetation patches, distributed across four regions. Soil seed banks stored the most germinable species of the three seed bank types, although these were dominated largely by annual herbaceous species. High abundances of seedlings emerged from scat samples, indicating that native animals, such as kangaroos and emus, play a role in transporting seeds in these landscapes. Finally, leaf litter stored the most germinable propagules of woody species, therefore, representing a vital mechanism for woody vegetation regeneration. There were few differences in emerging seedling assemblages in terms of species richness, abundance or composition between seed banks of old-fields and adjacent remnant vegetation, suggesting that old-field seed banks have a high level of resilience. Our findings suggest that these seed banks can make an important contribution to natural regeneration of these old-fields, but mainly with respect to understory and midstory species, with overstory tree species mostly absent from these seed sources.

Automated summary

This study investigated the regenerative capacity of old-fields in semi-arid floodplains of eastern Australia through a year-long seedling emergence experiment, revealing that soil, leaf litter, and animal scats all contain rich germinable species. Overstory tree species are mainly absent from these seed sources, but they play an important role in the regeneration of understory and midstory species.