Beach and Dune - Gower - page 141

FIG 74. The largest shingle structure in Gower, the three-ridge shingle beach at Pwlldu. (David Painter)
the Gower Commons Initiative for Figure
Although shingle beaches may appear to be harsh environments, most formations of coastal shingle
are partially vegetated; indeed this is the natural condition unless the shingle is regularly mobile. This ve-
getation can be abundant even if it is not species-rich. In particular shingle beaches provide an important
habitatforlichensand,toalesserextent,forbryophytes(mossesandliverworts).Thepebblesthemselves
often support intricate mosaics of micro-lichens. There is an equivalent zonation of lichen to that found
onrockycoasts,wheretheintertidalzoneisblack,followedbyanorangezoneandthenabovethehighest
tides a grey zone, although this zonation is less obvious on the shingle. In the intertidal zone pebbles
are sometimes covered with the black thallus of black tar lichen and the nationally rare Verrucaria dit-
marsica . Above this is a community of leafy yellow scales lichen and occasional Caloplaca spp., which
generallyoccursatthelevelofthehighestspringtides.Whileonrockyshoresthegreyzonemaybedom-
inated by Ramalina species, on shingle there may be another black zone largely dominated by Rhizocar-
pon richardii . In some places this is succeeded by 'lichen heath', but for a variety of reasons it is rare to
find a complete sequence, and the lichen communities of the Gower shingle are no exception to this. It is
difficult to recognise a similar zonation pattern in the bryophytes, but there is clearly a transition from the
unstable and saline foreshore where no bryophytes are present, through the heathy short turfs dominated
by Hypnum spp.,tothespecies-poorcommunitiesinthecoarsegrasslandsonthelandwardsideofshingle
bars.
Shingle structures sufficiently stable to support perennial vegetation are a comparatively rare feature
anywhere in Britain, and in this context the beach at Pwlldu is especially significant for the wide range of
plants that occur, ranging from pioneer communities through to scrub. The classic pioneer species on the
seaward edge include sea pea Lathyrus japonicus , Babington's orache Atriplex glabriuscula , sea beet and
sea campion. There are no recent records of another pioneer, sea kale Crambe maritima , but it may still