Beach and Dune - Gower - page 143

ter associated with shingle structures is saline, but the presence of fresh water near the shingle surface,
such as that supplied by the Bishopston Pill at Pwlldu, creates conditions required by a range of species.
Variations and fluctuations in the height and chemistry of this water table have an enormous influence on
which invertebrate species are present.
Several of the groups occurring on shingle, such ants and orb-weaving spiders, rely entirely on the
structure provided by vegetation, while many invertebrates rely on vegetation as a direct food source.
Many of the plant species also have their own particular groups of specialist invertebrates. Sea beet in
particular supports a range of animals including the rare weevil Lixus scabricollis and the beet moth
Scrobipalpa ocellatella . Sea campion forms small mats of vegetation on the surface of the shingle that
provide shelter to a number of invertebrate species, including, elsewhere in Britain, the tortoise beetle
Cassida hemisphaerica and the moth Carocolum vicinella , but there are no records of these species to
date.
Shingle structures elsewhere in Britain can support large numbers of breeding birds, including gulls,
waders and terns, but for most of the year there are too many people on the Gower beaches. As on the
sandy beaches, the ringed plover is one of the few birds that attempts to nest in this habitat.
SAND DUNES
LikemostofthedunesystemsinWales,noneoftheGowerdunesystemsisentirelynatural,althoughnat-
ural processes have obviously been responsible for their formation. The most unaltered parts of the dune
are those immediately behind the beach, where the physical processes take place without being affected
by human activities. Further inland, however, the vegetation of most of the dunes has been altered by a
long history of grazing by sheep, cattle and rabbits, though information on this is sparse. This interven-
tionhasproducedacomplexmosaicofsemi-fixeddunes,dunegrasslandandevensometimesduneheath,
all of which are important semi-natural habitats. Dune heathland is very rare in Wales and there are only
41 hectares in the whole of the country, one of the main areas being Pennard Burrows. In the absence of
grazing some areas of stable dune would probably have developed into scrub. There are no examples in
Britain of primary dune woodland, although it would have been present before clearance by early people.
In general it is the larger dune systems such as Llangennith and Broughton Burrows that are the most nat-
ural while the smaller dune systems, such as Penmaen and Pennard Burrows, tend to be heavily modified
by heavy visitor pressure or grazing.
Sanddunescanbedividedintofourdifferenttypes,dependingonthecircumstancesunderwhichthey
have formed: bay dunes, climbing dunes, spit dunes and hindshore dunes. All four types can be found
in Gower (Table 7), and some dune systems are a combination of one or more, the prime example being
NicholastonBurrows,whichhasfeaturesofspit,bayandclimbingdunes.Baydunes,thecommonesttype
in South Wales, develop from sand trapped within the shelter of rock headlands, the classic example in
Gower being Port-Eynon and Horton dunes. In contrast the hindshore dunes, such as Oxwich, develop
behind beaches that have a good sand supply and a prevailing wind which is onshore and which drives
sand inland to form a series of dune ridges or mobile parabolic dunes. These dunes are often found on the
most exposed areas of the coast. Spit dunes like Whiteford develop at the mouths of estuaries and depend
mainly on river sediment for their supply of sand. Finally climbing dunes such as those at Pennard and
Penmaen Burrows are the result of sand being blown up onto terrain inland of the main dune system and,
inthiscase,coveringlargeareasofsteepcliff.Thesandoftenonlyformsathinveneerandtheunderlying
rock exerts a strong influence on the plant communities that exist.
TABLE 7. Sand-dune systems in Gower. (Adapted from Barne et al ., 1995)