Question: How resilient is the seed bank of an invaded dune system? Is that resilience dependent on duration of invasion? How does the accumulated litter layer contribute to the soil seed bank?
Location: Coastal sand dunes invaded by Acacia longifolia, Portugal.
Methods: Seedling emergence was used to quantify and compare soil seed banks in long-invaded, recently invaded and non-invaded areas. Changes in seed banks were also compared with areas where A. longifolia and the litter layer were removed.
Results: Species richness, seedling density and diversity were higher in non-invaded and recently-invaded areas than in long-invaded areas. Although there was an apparent similarity between non-invaded and recently-invaded areas, analyses of species traits revealed differences. Non-invaded areas had a wider array of traits. Exotic/invasive species dominated invaded seed banks while native species dominated non-invaded seed banks. Life forms, growth forms, longevity and dispersal mode showed differences between areas, with cleared plots of long-invaded areas being apparently the most similar to non-invaded plots. Acacia longifolia seeds were most abundant in long-invaded areas, particularly where the litter layer remained. Removal of A. longifolia plus the litter had little effect on the seed bank composition of recently-invaded areas but resulted in noticeable changes in seed banks of long-invaded areas.
Conclusions: Long-invaded areas are less resilient and show a higher reinvasion potential, despite severe alteration of the seed banks of both areas. Seed bank studies can be a useful tool to guide management, but can give misleading results when invasion periods are protracted.