Moderate impacts of plant invasion and management regimes in coastal hind dune seed banks

Plant invaders may directly or indirectly affect ecosystem resilience through their impact on soil seed banks. The invaders, and the application of control measures, change seed bank dynamics by altering the number of seeds entering and leaving the seed bank. We tested the impact of bitou bush (Chrysanthemoides monilifera ssp. rotundata), on the seed bank. We examined seed banks in heavily-invaded, sparsely-invaded and managed dunes, where bitou bush biomass had been controlled. While management of bitou bush may have reduced the density of bitou bush seeds in the soil, it did not reduce the richness of other weed species. Native tree species richness was significantly higher in seed banks of sparsely-invaded than either heavily-invaded or managed sites, perhaps indicating a permanent shift in community structure following invasion. However, remaining indices of native seed bank diversity were similar across all invasion categories, indicating that seed banks of many native species were unaffected by both invasion and management. While examination of seed banks is informative in assessing past and potential community dynamics, low similarity between the standing vegetation and seed bank at all sites indicated that many hind dune species had other storage or regeneration modes and seed banks cannot be relied upon for comprehensive dune restoration.