Delfland Coast, The Netherlands
Photographed by Frank van der Meulen
This picture shows an interesting geomorphologic landscape feature. It is the result of the interplay between wind, sand and vegetation after a few stormy days in August 2014. Prevailing winds from the North Sea (left) have blown huge amounts of sand from the beach. This sand was trapped by a narrow line of Marram grass (left), even so much that the grass itself is almost buried. About 50-75 cm of sand was accumulated in a few days. In the lee-side behind these grasses, a kind of cuesta-shaped sand body is formed. The windward slope is gentle and rising, the leeward slope is steep (ca 60°) and caused by the gravity fall of dry sand grains (particle size is about 250-300 μ). This sand body is about 5-10 m wide and several 100 m in length. It follows the Marram that was planted here along the beach in long rows.
Marram is noted for its ability to trap sand. It is used all over the world to trap sand and build up and re-enforce dunes in a natural way. Re-enforced dunes, for example, afford better protection against coastal erosion and flooding. Why does Marram prefer sand accumulation? The fresh dune sand is exploited by new tapering roots of Marram for nutrients. Older, lower, sand layers in the fore dunes are infested by root-feeding nematodes and pathogenic microbes. They decrease the nutrient and water uptake capacity of the Marram roots. Plant species that naturally succeed Marram grass, such as Fescue and Sand sedge, are tolerant of the pathogens of Marram. However, in due time they also develop such soil-borne pathogens. This ecologic chain of plant-soil feedback interactions and consequences for succession in the fore dunes was demonstrated in The Netherlands in the 1980s and 1990s by Van der Putten (Oecologia, 1988 Nature, 1993). It stimulated new developments in ecologic theory.