The Worm, the Holms and the Mumbles - Gower - page 168

In 1977 two fenced enclosures were erected on the south side of the Inner Head to exclude grazing
animals, including rabbits, and over the past 27 years a thick layer of red fescue has developed, in stark
contrast to the shorter and more species-rich turf on the other side of the fence. Rabbits are present on all
oftheislands,andbyselectivelyfeedingoncertainplantstheycancompletelyaltertheirecology.Moder-
ate grazing by rabbits prevents any particular species dominating, especially vigorous and tall-growing
species, thus allowing the smaller species, which would normally be shaded out, to grow.
The dense turf of red fescue that has developed in the enclosed areas, the springy 'monstrous thick
grass' noted by Dylan Thomas, also covers the more sheltered parts of the Middle and Outer Heads. Turf
'mattresses' are a particular feature of ungrazed islands in southwest Britain and they may represent the
climaxvegetationofsomeexposedandungrazedseacliffs.Amongsttheredfescuecanbefoundseabeet,
sea mayweed Tripleurospermum maritimum , and abnormally large spring squill, with rock sea-spurrey
Spergularia rupicola , thrift and white clover where the grass is not so thick. A number of changes have
taken place since Professor McLean studied the area in 1935 and recorded that the turf was over half a
metre deep. Following the destruction by fire of a large area of ungrazed grassland on the Middle Head
in 1957, the Nature Conservancy reseeded the eroded soils with unimproved Danish red fescue in 1958.
The plants established sufficiently to prevent serious soil erosion during the following winter, but by the
summer of 1959 they were dying and as they did so the native species re-established itself. Perhaps as a
result of the fire red fescue no longer forms a 'largely pure' turf on the Middle and Outer Head, and it
is now associated with abundant creeping thistle Cirsium arvense and smooth meadow-grass, neither of
whichwasobservedbyMcLean,togetherwithmanyotherspecies-asimilarplantcommunity,infact,to
that found on parts of the Inner Head, despite the presence of sheep. High up on the slope of the southern
side of the Inner Head, the red fescue mattresses gradually give way to limestone heath and grassland.
Theaspectandshelterfromtheprevailingsouthwesterlywindsalsocontributestothecharacterofthe
grassland on the north side of the Inner Head. Here salt deposition is reduced, with the result that there
arefewermaritimespeciesthanwouldnormallybeexpectedinsuchanexposedlocation.Thereisanarea
of bracken and bramble at the eastern end of the Inner Head, which is monitored to ensure that the more
valuable grassland communities are not reduced. Although bracken is an extremely invasive plant there
are a few areas where it cannot colonise, including places exposed to large amounts of salt spray, but as
areasaresheltereditisaproblemandabletoadvanceintowhatwouldseemtobeveryexposedlocations.
This is because salt damage is dependent on summer storms; winter storms have little or no impact on the
buried rhizomes. Bracken was unrecorded in a botanical survey of the Worm carried out by the Reverend
Riddelsdell in 1910, but by the end of the 1960s it covered an area of 1,000 square metres on the south-
eastern side of the Inner Head.
During his botanical survey the Reverend Riddelsdell found that the Outer Head was almost entirely
covered by thrift and sea campion. Also present were sea storksbill Erodium maritimum , bluebell Hyan-
thoides non-scripta and cowslip. The latter, described as common and abundant by Riddelsdell, is still
present, along with the gorse on the eastern end of the Inner Head. The eastern end of Middle Head was
stated to be 'bright red to the distant observer with masses of sorrel'. Gulls started to nest on the Worm
towards the end of the nineteenth century and it seems that the dense sheep's sorrel Rumex acetosa was a
result of this.
Gulls and other colonial seabirds, such as puffins, can have major effects on the vegetation of islands.
This is due mainly to the deposition of guano and the physical damage caused by trampling and extract-
ing nest material. Although guano is very rich in nutrients and may initially stimulate plant growth, as
the nutrient levels increase the soil eventually becomes toxic and unable to support plant life. However,
buck's horn plantain, sea campion, spear-leaved orache Atriplex prostrata , sea mayweed, sea beet, com-
mon scurvygrass and sheep's sorrel may grow abundantly in moderate concentrations of guano. Mary