Frequent inundation helps counteract land use impacts on wetland propagule banks

Abstract

Question: How do contrasting influences of inundation and historical land uses affect restoration of soil propagule bank composition in floodplain wetlands? Location: Northern Nature Reserve (large ephemeral floodplain), Macquarie Marshes, New South Wales, Australia.

Methods: We conducted germination assays on soil samples collected from fields with different land-use histories, stratified along an inundation gradient. We used GLM to determine whether native and exotic species richness and abundance varied along gradients of inundation and land use.

Results: Species richness and plant abundance in soil propagule banks were positively related to inundation and negatively related to intense historic land use. The abundance of native species was significantly higher in more frequently inundated areas. Abundances of exotic and ruderal species were higher in areas of intense prior land use. Overall species richness was generally similar across land-use histories.

Conclusions: Land-use legacies compromised the ability of propagule banks to rejuvenate native vegetation in this floodplain wetland, especially in less frequently flooded parts of the floodplain, which harboured more ruderal and exotic species. Negative effects of prior land use may be alleviated by increased inundation. Native soil propagule banks were remarkably intact, providing a reservoir for restoration of wetland vegetation, even in soils highly disturbed by up to 20 yr of agricultural cropping. With appropriate inundation, soil propagule banks in less degraded areas of the Macquarie Marshes can provide diverse mixtures of desired species in high abundance but, in highly degraded areas, full restoration may be delayed.