Beach and Dune - Gower - page 142

occurinGower,whereitgrewinatleastonelocalityinthe1950s.Heathlandcommunitiesareparticularly
rare on shingle, but here heather Calluna vulgaris and lichen Cladonia impexa heath is present and wet
heath with common reed Phragmites australis and water mint Mentha aquatica also occurs. It is interest-
ingthat thewoodyspecies atPwlldu,suchasblackthorn andcommon ivy Hedera helix ,growinisolation
out of the bare shingle. The occurrence of these species and the general lack of soil at Pwlldu suggest that
humus may be less important in vegetational development on shingle than previously thought, and that
the level of moisture retention in the shingle is probably a more crucial factor. The amount of vegetation
cover, which has a mulching effect, may therefore be more important than soil in the further development
of plant communities on this site.
AtPennardthesmallsandyshinglespitsupportsarangeoftypicalspeciesincludingseaholly Eryngi-
um maritimum , sea sandwort and common orache Atriplex patula . Unlike Pwlldu, Pennard Burrows are
registeredcommonlandandgrazedbycattleandponies,andthisproducesashortswardwithapoorrange
of plants. There are also high levels of recreational pressure, with fires of driftwood regularly being lit
duringthesummermonths.Theshingleisoftendisturbedinthisprocesstomake'fire-pits'andduringthe
early 1990s a considerable amount of shingle was moved to the area of salt marsh behind to make a stone
maze or labyrinth, but this has now been covered by the shingle moving inland. The shingle beach that
once existed at Salthouse Point had a pioneer community of thrift, sea bindweed Calystegia soldanella ,
silverweed Potentilla anserina , small toadflax Chaenorhinum minus , common saltmarsh-grass and wild
thyme,withredfescueandspeciesofplantains Plantago spp.,clovers Trifolium spp.anddock Rumex spp.
nearer the shore. Finally at Whiteford there are some quite extensive well-vegetated and stable shingle
'recurves', with a good range of plants including lichens, extending southwards from the main dune and
shingle spit into the salt marsh at Berges Island.
While the plant communities of shingle are quite well known there is little information on the animal
communities, particularly the invertebrates. From what is known, however, the invertebrate fauna of
shingle has some remarkable characteristics. While it consists of only a limited number of species, partic-
ularlyinareasofopenshingle,thecommunityincludesahighnumberofrarities.Oneofthekeyelements
is the very distinctive structure ofshingle, and while at first glance areas ofpure unvegetated shingle may
appearsimple,atasmallscalethehabitatishighlycomplex,withlargespacesbetweenthepebbles.These
spacesprovideanunusualandsecurehabitat wherespiderscanconstructwebsandotherspeciescanhide
from threats on the surface. They also provide protection from the weather, and deep in the shingle there
are stable, humid conditions. The microclimate and structure of open shingle seems particularly to favour
the hunting strategies of jumping spiders, and a rich group can be found. Species recorded elsewhere in
Britain include Phlegra fasciata , which has been found on Pennard West Cliff and Horton Cliff, and the
woodlouse spider Dysdera crocata , found on Llangennith Burrows. As yet, however, there are no records
of these species from shingle sites in Wales.
Inadditiontocreatingtheshinglehabitattheseaprovidesanumberofotherfeaturesthatareexploited
byinvertebrates.Thereisadetritus-basedecosystemalongthedecomposingstrandline,includinganimals
such as the common sandhopper Orchestia gammarella , which occurs in great numbers. Like those on
sandybeachesthestrandlinesofshinglebeachesarealsoofparticularimportanceforwoodlice.Woodlice
have evolved from marine species (to which they are quite closely related) and are well suited to living
on shingle beaches. Other common inhabitants of the high water mark and just above include spring-
tails, mites, the common earwig Forficula auricularia , ground beetles, rove beetles, millipedes such as
Brachyiulus pusillus and centipedes. Many of these strandline predators move out in favourable condi-
tions to forage in the surrounding area. Strandlines on different shingle sediments and with different con-
stituents contain different assemblages of invertebrates. There is still much to be discovered about the
invertebrates of the Gower shingle and the sites would benefit from detailed surveying. Most groundwa-