Soil seed banks in degraded riparian zones: Friend or foe?

The restoration and management of riparian plant communities and riparian zones is the dominant focus of river restoration efforts globally. While soil seed banks are understood to be integral to the vegetation dynamics and restoration of many ecosystems, little is known of their role in riparian zones, particularly in lowland areas. This study investigates soil seed banks of riparian zones adjacent to small lowland streams and their potential to influence riparian restoration. We compared the composition and structure of the viable soil seed bank between cleared and wooded reaches along three lowland creeks in south-eastern Australia. The viable soil seed bank was characterised using the seedling emergence method and compared to environmental variables and the extant vegetation. Riparian condition (i.e., cleared or wooded) and the distance from the channel both explained the variation in many characteristics of the soil seed bank, including the total number of germinants, species and overall community composition. Stream reaches cleared of riparian vegetation had significantly more species than wooded reaches. Community composition of the soil seed bank was significantly correlated with site openness and was generally dissimilar to the extant vegetation. The floristic composition of the extant vegetation may be less important than structural characteristics in influencing soil seed bank dynamics within these environments. The soil seed bank contributes to the diversity of vegetation in these riparian zones. However, recruitment from the soil seed bank will contribute toward restoring only some components of riparian plant communities and may detract from restoration by introducing undesirable species.