Seed-bank dynamics in the invasive plant, Ambrosia artemisiifolia L.

The seed-bank dynamics of Ambrosia artemisiifolia (Asteraceae), an annual invasive plant introduced from North America to Europe, were studied in nine French populations developing in field crops, set-asides or wastelands. The vertical distribution of seeds was studied in two different depth sections (0-5 cm and 5-20 cm), and the spatial horizontal pattern of distribution was analysed for two selected field-crop and set-aside populations. The proportions of dormant, non-dormant and dead seeds, as well as the changes in seed-bank dormancy overtime, were evaluated. Natural seedling recruitment and its variation under different disturbance treatments in competitive set-asides were also studied. From 536 +/- 194 to 4477 +/- 717 seeds m(-2) were found in the living seed bank (0-20cm). The majority of seeds in field crops was found in the lower soil layer, whereas the opposite pattern was observed in set-asides and wastelands. Dormant seed proportions were low (0-18%) before natural germination, but then regularly increased. The seed bank of A. artemisiifolia was spatially aggregated irrespective of the extent of soil disturbance. On average, 23 +/- 12 to 292 +/- 62 seedlings M 2 were recorded, with densities lower in set-asides than in field crops and wastelands. Seedling densities were not correlated to upper seed densities except for two field crops. Soil disturbance and the removal of vegetation had positive effects on seedling recruitment in set-asides. Seed-bank dynamics appear to be crucial in the invasive success of A. artemisiifolia, and this knowledge will provide insights for the management of the species.