Environmental Engineering Reference
In-Depth Information
sheltered places. This issue of 'agricultural eutrophication' on the south Gower coast was the subject of
a detailed study (Etherington and Clark, 1987) which focused on the stretch of cliff from Worms Head to
Port-Eynon,partofwhichiscommonland.Theconclusionwasthatsince1935therehadbeenareduction
in cover and abundance of prostrate species such as wild thyme, common bird's-foot-trefoil
Lotus cor-
niculatus
, squinancywort
Asperula cynanchica
, common rock-rose and the rare hoary rock-rose, and an
increase in agricultural weeds and perennial rye-grass. The increase in rye-grass is particularly dramatic
asitwasnotpresentin1935,butitisnowacommoncomponentofthegrassland.Thedeteriorationofthe
botanical interest is due to an increase in the number of sheep grazing on the clifftop commons, coupled
withtheapplicationoffertiliserstoadjacentfieldsandcertainareasofthegrassland.Thesepracticeshave
led to an unparalleled increase in plant nutrients, both from inorganic fertilisers and from sheep urine and
dung. The species that have declined cannot tolerate competition from tall, fast-growing species, which
are favoured by the high nutrient levels.
FIG
48
. Sheep grazing on the Gower cliffs. Overgrazing of these slopes is a serious conservation issue. (David Paint-
er)
Agricultural intensification east of Mewslade has long been of concern to conservation organisations,
and several recent studies have been directed towards obtaining a clearer understanding of processes
(Etherington and Clark, 1987; Dawson, 1989). Reseeding of clifftop grasslands and subsequent fertiliser
applications have caused noticeable changes in semi-natural communities in many areas and there have
been many negotiations with the graziers directed towards reducing these impacts. Such eutrophication is
farlessobviouswithintheNationalNatureReserveandtheplaceswhereitdoesoccurareusuallycloseto
the areas used for stock feeding. Elsewhere, grazing continues to exert an impact by modifying the flora
ofthelimestone grassland(bloodycrane's-billandgreaterknapweedareparticularly sensitivetograzing)
and by preventing a succession to gorse scrub in the more sheltered areas. In contrast Horton Cliffs and
Slade Cliffs have valuable patches of limestone grassland, but parts of these are becoming scrubbed over,
