From a nature conservation point of view sand dunes, along with saltmarshes, are often considered to be amongst the most natural habitats. They are formed wherever there is a suitable supply of sediment within the size range 0.2 – 2.0 mm, sand availability as well as mobility are key components in sand dune development. They may defined as: areas where wind blown sand is deposited inland from a wide beach which dries out periodically. Accumulations a few centimetres to 40 metres or more thick are the norm and can be formed by the combined action of wind and the stabilising effects of vegetation1. Coastal sand dunes can be categorised according to their geomorphological structure.
The aeolian sand mobility is also important for the regular creation of young vegetation, where the succession towards older and more nature vegetation can start again and again. However, traditionally dunes have been stabilised on a wide scale because mobility of sand has often been considered a threat to human interests (see: Stabilisation management). Nowadays the recognition of the importance of dynamics in the coastal environment has grown and management has changed to ‘dynamic preservation’(1) (see: Natural foredunes, Mobile dunes and blow-outs).
 

 1- Natural foredunes

Foredunes are shore-parallel, convex, symmetric to asymmetric dune ridges formed on the top of the backshore. Generally they have been classified into two main types: incipient and established foredunes. The coastal foredune actively exchanges sediment with the beach (4). The development is related to the erosional scenarios of the shoreline which alternates with stabilisation due to several biogenic factors (see: Houstrop, Denmark & the island Mellum, Germany). In places where dunes are several kilometres wide the sand dune body is often much bigger than the necessary storm surge defence profile. In these systems coastal defence is not critical and there is room for natural processes: the outer dune ridges can be allowed to develop into more natural foredunes through sand mobility like on Spiekeroog (Germany), Schiermonnikoog (The Netherlands) and in Sefton (England). This “dynamic” approach is leading to the development of more or less natural beaches. This way of management is usually considered positive and not a threat to coastal defence policy.

  2- Mobile dunes and blow-outs

Dunes are natural and dynamic systems which are characterised by a certain mobility of sand in parts of the area. Cycles of wind erosion followed by periods of stability are all part of the natural development of dunes (1). In natural coastal dune environments blowouts are commonly found. They may be initiated in a variety of ways and their development is not restricted to eroding coasts (4). There are a number of dune systems, which have maintained their large-scale dune mobility for a long time already. Examples are: Coto Doñana (Spain), Rabjerg Mile (Denmark) and Slowinski (Poland). These forms of naturalness will enlarge ecological variety because of the maintainance of pioneer situations. On the East Frisian Islands (Germany) mobile dunes and blowouts are left to develop in designated nature zones, which are not crucial for sea defence. These experiments were often considered very successful, as well as in Belgium (Flemish coast). In some places local communities and dune managers have agreed to control the natural dynamic processes (see: Stabilisation management), e.g. in the Furreby dunes (Denmark) and Cap Ferret (France). Over the last years some experiments started in France (Merlimont) and in the Netherlands (Meijendel dunes, Midden Heerenduin) to stimulate blow-outs and sand drift.

   3 – Stabilisation management

Mobility of sand dunes has often been considered a threat to human interests and consequently in most dune areas large-scale dune mobility has been effectively controlled since 1900. Dunes can be artificially created and stabilised to prevent sand drift and inundation of human facilities, provide a predictable barrier against wave overwash and flooding and provide a barrier to salt spray that can help maintain the existing biological inventory (see: Griend, The Netherlands). The most common techniques used to trap sand are employment of sand fences and planting of vegetation (see: Flemish Coast, Belgium; Memmert, Germany) (2). Marram grass (Ammophila arenaria) is used most commonly since the fourteenth or fifteenth century. Plants are usually taken by thinning natural areas of dense growth but the cultivation of grasses can have many advantages (see: Norderney, Germany) (3). The method of establishing marram grass can influence the vegetation development during further succession (see: Voorne, The Netherlands) (5). However, Marram grass does not thrive in artificially stabilised areas where burial by sand is prevented (see: Oostvoorne – Noordwijk – Oostkapelle, The Netherlands). Planting the area may attract seagulls to breed there (Larus spec.). These birds enrich their habitats with the nutrient N which fertilizes vegetation for dune development (see: Mellum, Memmert, Germany). Furthermore, dunes were traditionally stabilised by trees, especially by Pine tree (Pinus spec.) (see: Anholt, Denmark). With the plantation of pine trees in combination with Marram grass many dune complexes have been stabilised. The combined effect has been a dramatic decrease of pioneer and young vegetation communities.
 
 
 
 
 

 

References:

1. Doody (2000): Coastal conservation and management. An ecological perspective.
2. Nordstrom, K.F. (2000): Beaches and Dunes of Developed Coasts. Cambridge University Press. (PC2000a).
3. Schulze Dieckhoff, M. (1992): Propagating dune grasses by cultivation for dune conservation purposes. In: Carter, Curtis & Sheehy-Skeffington (eds.). Coastal Dunes: 273-281. Balkema. Rotterdam. (BCD92).
4. Short; A.D. (1999): Handbook of Beach and Shoreface Morphodynamics. John Wiley & Sons, LTD. UK. (BCD99).
5. van der Laan, D., O.F.R. van Tongeren, W.H. Putten & G. Veenbaas (1997): Vegetation development in  coastal foredunes in relation to methods of establishing marram grass (Ammophila arenaria). Journal of Coastal Conservation 3: 179-190. EUCC. Opulus Press Uppsala. Sweden. (KJc97b).