Carmarthen Bay Dunes/ Twyni Bae Caerfyrddin IPA
Location: To the east of Carmarthen Bay, around the estuary of the Afon Tywi, west of the A484.
Grid Reference: SN 365 051
Carmarthen Bay Dunes IPA has been recognised as one of 165 Important Plant Areas in the UK.
The key features of this IPA are:
Dunes with creeping willow;
Very young mobile dunes;
Humid dune slacks;
Shifting dunes along the shoreline
This IPA is one of two major sand dune systems in Carmarthen Bay, on the South Wales coast, alongside the estuary mouths of the Rivers Taf, Tywi and Gwendraeth.
Sand dunes form where dry sand is regularly blown towards land from the beach and is deposited above the high-tide mark. It can then be trapped by specialised dune-building grasses (e.g. marram), before eventually being colonised by other plants that help to stabilise the sand and ‘fix’ the dune. Wales is important for its sand dunes, the formation of which is strongly influenced by the prevailing westerly winds that help create a series of large ridges separated by wetter ‘slacks’. As you move away from the sea you pass through various zones: mobile and semi-fixed dunes are followed by fixed grassland dunes and scrub. Sand dune systems can support an extremely diverse range of plants and provide a habitat for a variety of specially adapted species, including a number of uncommon plants and fungi.
The extensive dune system has ridges that are divided by intervening deep and damp hollows which are exceptionally rich in rare or uncommon plants. Along the seaward edge of the dunes is a fairly narrow zone of open grassland dominated by sand couch grass. Inland, marram grass becomes more dominant, grading into semi-fixed dunes where the marram grass is mixed with restharrow, dewberry and red fescue, and a variety of species including wild pansy and lesser meadow-rue.
Marram grass becomes much less frequent further from the sea in the area of stable ‘grey’ dunes where false oat-grass and dewberry occur, together with the invasive sea buckthorn. Orchids of the dry dune grassland include the pyramidal orchid and autumn lady’s-tresses. The dune-slacks that occur between the ridges formed by the higher dunes vary in character according to the length of time that they are covered by water. There is much creeping willow and the ground is often carpeted with mosses. These dune-slack communities are characterised by the frequency of such species as variegated horsetail, the moss Calliergon cuspidatum and common fleabane. Species of flowering plants include the nationally rare fen orchid, growing amongst an abundance of marsh helleborine and marsh orchids. Other orchids to be found in these dune slacks include frog orchid and fragrant orchid.
The dune gentian, known only from six sites in Britain, also grows in the IPA at Laugharne Burrows. The dunes as a whole are also important for lower plants, the rare liverwort, petalwort, occurring here, and fungi are represented by a diversity of rare or threatened species, including some not previously recorded in this country, such as Inocybe salicis.