Early vegetation succession and management options on a brackish sediment dike

Port authorities worldwide are confronted with a continuous stream of dredged sediment that needs to be disposed. One of the solutions being considered for the Port of Antwerp (Belgium) is the beneficial use of constructing landscape dikes with dredged material. This paper examines whether spontaneous development, whether or not combined with mowing or sowing, is a valuable alternative to afforestation for revalorizing brackish sediment dikes. Early vegetation succession was followed on an experimental dike along the river Scheldt. The pioneer vegetation was closely related to flood-mark communities of the Atriplicetum littoralis. The most important abiotic variables for determining consecutive development were the salt gradient originating along the topographic gradient, and the mowing management. When halophytic pioneer species have disappeared, the successional pathways on dredged-sediment dikes are very similar to those described for other hyper-eutrophicated soils, such as abandoned arable fields. Zero-management results in species-poor Urtica-Elymus stands. Mowing and cut removal leads to ruderal grassland related to the Artemisietea. Grass species need to be sown to obtain target communities of the Arrhenatherion. The consequences of these findings for the construction, design and management of future landscape dikes are discussed.