NWT Holme Dunes by Tasha North
Sea holly by David North
Coastal sand dunes
Sand dunes along the North and East Norfolk coasts are formed when onshore winds, carrying sand from the beach, are interrupted by material lying at the top of the beach and caused to drop the sand they are carrying. Initially these embryo dunes are colonised by hardy pioneer plants which are able to cope with the well-drained, wind-blown and often salty conditions. These include prickly saltwort, sea rocket and sea sandwort.
The major dune-building is done by marram grass, which is adapted to grow up through blown sand which covers it, thus building the height of the dune and stabilising it. This stage is generally referred to as the yellow dune. As yellow dunes mature, increasing in organic matter and becoming protected from onshore wind and salt by new dunes forming towards the beach, they are colonised by many plant species and, depending on local soil and water conditions, can come to resemble acid heaths or chalk grasslands. This stage is known as the grey dune. The dunes of North West Norfolk are unusual in being rather alkaline, thanks to the presence of plentiful bivalve shells, and have a flora which is more similar to a chalk grassland’s, including harebell, bird’s-foot trefoil and pyramidal orchid. The dunes of East Norfolk, by contrast, are more acidic and tend, with age, to resemble heaths or acid grasslands, with common ling and sheep’s-bit being typical here. Grey dunes are also home to many invertebrate species, including dark green fritillary, grayling, small copper and mottled grasshopper.
As dunes grow old and lose height, thanks to erosion by the wind, they often develop low-lying areas, known as dune slacks, where water collects. The nature of these slacks depends on the acidity of the dune and the water table, but wherever they occur dune slacks develop a fascinating flora and fauna. Many orchid species are typical, including common spotted orchids, southern marsh orchids, marsh helleborines and, in some sites, the beautiful coccinea form of the early marsh orchid. Living among these plants there are often locally uncommon species of dragonfly including common hawker and, exceptionally, yellow-winged or red-veined darter. Where ephemeral pools occur, which do not allow the development of predatory species such as fish and larger amphibians, the rare and highly protected natterjack toad breeds.