Keywords:
island barrier dune
foredune
natural dynamics
tidal inlet

Location:  The Netherlands, Province of Friesland, Schiermonnikoog

The Wadden Island Schiermonnikoog
Schiermonnikoog is a barrier island in the Dutch Wadden Sea. Dunes, salt marshes and mud flats are the main habitats. Since 1989, the island has been a National Park with Natuurmonumenten as the manager, the Dutch national society for nature conservation. All in all, the National Park covers an area of approximately 2500 ha, the village Schiermonnikoog and farmland are excluded.
In 1990, the Government and Parliament of the Netherlands adopted a new national policy for coastal defence: dynamic preservation of the coastline. One part of the plan points at the importance of the preservation of the natural dynamics of the foredunes as an ecological main structure of the Netherlands. Schiemonnikoog is one of the selected areas in the Dutch coastal dune belt, where natural developments are possible without risks for sea defence.

Management
Until the late 1950s the study area was an almost bare sand flat with scattered young dunes up to 2 m high. In 1959, an approximately 5 m high sand dike was constructed which cut off the area from the direct influence of the sea, so plant colonisation started. In 1972 the coastal defence authorities decided to keep a gap in the dike open, that had resulted from a heavy winter storm. Additionally, the maintenance of the dike to the east of this gap was ceased. From this time on the area would be subject to irregular flooding and sand mobility.
To reconstruct the vegetation succession over a 42-year period, the Laboratory of Plant Ecology, University of Groningen, together with the Department of Ecology and Ecotoxicology, Free University of Amsterdam, analysed vegetation maps of six different years and data from a permanent plot using a Geographical Information System.

Results
Heavy storms and associated processes such as sand blowing, intensive flooding and increased salinity have created a disturbance / stress gradient of progressive and regressive succession across the beach plain. In certain places the vegetation cover has repeatedly been destroyed and succession reinitiated, whereas certain parts seem to have changed little and others have developed grassland and scrub cover. The lack of management with the aim to stabilise wind and water movements has led to the formation of a tidal inlet with a positive effect for both biodiversity and certain endangered pioneer species. It is concluded that the different stages of succession and associated diversity of plant species only can persist through the maintenance of the natural dynamics of the area.
 

The Wadden island of Schiermonnikoog with the study area and the position of the sand dike indicated

References

• Dommerholt, H. (1998): Management in the National Park of Schiermonnikoog by Natuurmonumenten. In: Drees (ed.). Coastal Dunes – Recreation and Planning. EUCC. Leiden. The Netherlands.
• Hillen, R. & P. Roelse (1995): Dynamic preservation of the coastline in the Netherlands. Journal of Costal Conservation 1: 17-28. EUCC. Opulus Press Uppsala. Sweden. (KJc95a).
• Janssen, M.P. (1995): Coastal Management: Restoration of Natural Processes in Foredunes. In: Healy &  M. Doody (eds.). Directions in European Coastal Management. Samara Publishing Limited. Cardigan. (PC95).
• van der Veen, A., A.P. Grootjans, J. de Jong & J. Rozema (1997): Reconstruction of an interrupted primary beach plain succession using a Geographical Information System. Journal of Coastal Conservation 3: 71-78. EUCC. Opulus Press Uppsala. Sweden. (KJc97).