Soil seed bank of calamine sites in Belgium: what could be learned for original metallophytes communities restoration?

Metalliferous sites often host rare, ecologically endemic taxa adapted to high levels of heavy metals in soils. In Belgium, these sites correspond to Calamine sites. They are often considered as waste ground dangerous for human health and public authorities are inclined to promote site remediation by fertilization, ground supply or removal, building ... In the present study, we analysed the seed bank of two ancient calamine sites in order to precise strategies for restoration of calamine original communities by top soil removal and perturbation. Composite soil samples were taken in 5 facies in two sites corresponding to different association. Cores were divided in three layers: litter, 0-5 cm, 5-10 cm. The total number of taxa was 24 taxa at Theux and 15 at Schmalgraf. The most abundant species (68%) are Agrostis capillaries and Viola calaminaria. Seed bank composition appeared different between facies except for three species. The seed bank was dominated by pseudo metallophytes species in Schmalgraf and by metallophytes or other species in Theux. The majority of the species didn’t present significant difference of number of seed between the three layers, except seven species (A. capillaries, V. calaminaria, Silene vulgaris, Minuertia verna, ...) with significant lower number of seed in the layer 5-10 cm. Our result showed that soil seed bank composition reflect well vegetation communities of the two sites. In addition, because pseudo-metallophyte species as Agrostis capillaries dominated seed bank when they were present in the vegetation, soil removal must be used with parsimony to restore original communities.