Contribution of soil seed banks to vegetation resilience in coastal freshwater wetlands of subtropical Australia

Abstract

Questions: What role do soil seed banks play in the resilience of coastal freshwater wetland vegetation communities? How might soil seed bank composition and similarity to standing vegetation drive changes in vegetation expression, particularly given projected changes in climate?. Location: Sixty wooded coastal freshwater wetlands in southeast Queensland, Australia. Methods: We surveyed standing vegetation and investigated soil seed bank composition through an 8-month-long emergence experiment. Results: Soil seed bank assemblages were dominated by forb and sedge species (23% exotic), but composition varied throughout the study region. Spatial (north–south) and land-use (urban–rural) gradients explained some variation in soil seed bank composition. Soil moisture and groundwater dependence also influenced species distributions, particularly for freshwater wetland species. The similarity of soil seed banks to standing vegetation was low. Species present in both extant and soil seed bank assemblages were commonly native wetland taxa, including one salt marsh species (Juncus kraussii). Conclusions: Projected climatic changes will likely drive changes in coastal freshwater wetland vegetation communities through increases in the frequency and intensity of disturbances (e.g., storm surge). Our results suggest that regeneration from soil seed banks could promote four potential scenarios: (1) expansion of weed communities, (2) expansion of salt marsh communities, (3) maintenance and expansion of wetland/terrestrial species, and (4) transformation to an unvegetated open water zone because of reduced regeneration success under changing conditions. These diverse vegetation futures highlight the vulnerability of wooded coastal freshwater wetlands and the need for research and management interventions to maintain their biodiversity and ecosystem services.