| Summary: | International audience The dunes of Berck- Merlimont, corresponding to the northern limit of the Picard coastal plain, is nowadays one of the most exceptionalsedimentary assemblages of European coasts , particularly representative of the North-Atlantic coastal dune oligotrophic vegetation systems.It extends to about five kilometers inland and consists of two series of sand ridges built at different times, the innermost rising to over40 m. These two ridges isolate a wide interdunal plain patterned by a complex microtopography, likely to be a former fluvio-marine environmentwhich was lastly covered in aeolian sand. Within each of both ridges and the plain we see numerous more or less flooded depressions,either naturally hollowed out by wind erosion or water ponds and holes of anthropogenic origin (former hunting ponds and bomb holes). Thisdiversity of geomorphological, hydrogeological and ecological conditions is causing the differentiation of several large systems of vegetation,sometimes highly specialized , developing from the foreshore and foredune towards the rear hygrophilous coastal forest and innermostxerophilous dune woodlands : 1 - System of the xerosere (dry dunes) of the coastal dunes, from the vegetation of foreshore to the grasslandand scrub of the back dunes, more or less affected by wind and salt spray; 2 - System of hygrosere of the dune slacks and interdunalplain, that can subdivided into two vegetation subsystems on mineral soils or organic to almost peaty soils; 3 - System of the non-floodedplain, mostly mesophilic (mesosere), housing very original sandy coastal grassland and natural or semi- natural meadows; 4 - System of thexerosere (dry dunes) of the inner ridge, more disturbed because widely planted with pines at a time (especially in communal dunes). Thediversity, originality and patrimonial value of each of these vegetation systems are presented and illustrated in this paper. Their genesis andnatural or anthropogenic evolution constitute the basis of discussion and guidance for ...
|
|---|