Environmental Engineering Reference
In-Depth Information
AREA ( HA )
SITE
DUNE TYPE
Broughton Dunes
Bay and climbing
224
Pennard Burrows
Bay and climbing
87
Penmaen Burrows
Climbing
17
Nicholaston Burrows
Spit, bay and climbing
17
Oxwich Burrows
Hindshore and spit
76
Port-Eynon and Horton
Bay
19
Whiteford Burrows
Spit
400
Total
840
DUNE ZONATION
At the beginning dune sand is rich in nutrients and calcium from crushed seashells, but these are soon
washed out by rain, so dunes, in contrast to the sand on the beach, are relatively low in nutrients. The
further from the shore, the fewer the nutrients in the sand, and this nutrient gradient is reflected in the
zonation of dune plants. Plants growing on dunes are also faced with two problems, an almost constant
shortage of water and the continual deposition of sand. Sand cannot store much moisture near the surface
and plants need a well-developed root to bring water from deeper levels or a mechanism to reduce evap-
oration. Most naturalists are familiar with the general zonation of dune habitats from the embryo dunes
to fixed dunes, but the processes of succession acting on the soils, plants and animals, geomorphological
changes and the fluctuations in water levels are less understood. In reality there are few clear boundaries
and one zone often blends into another across a gradient related to changes in one factor or another. In
particular, on most of the Gower dune systems there is no clear division between the mobile, or yellow,
dunes, and the fixed, or grey, dunes; instead there is a transition zone, which is often extensive. All of
the sand-dune systems have a rich flora including many local, interesting and rare plants as well as the
commoner dune species. Several hundred species of lichens, bryophytes, fungi and algae also occur. The
dune system at Whiteford has a particularly fascinating flora and is home to several nationally important
species of plant.
As described earlier, the embryo dunes, the first dunes above the high tide mark, are little more than
small piles of sand which have accumulated around obstacles such as pebbles or driftwood in the strand-
line. These dunes are easily destroyed byerosion bywind and sea and bytrampling, and are scarce onthe
heavily used beaches.
Behind the embryo dunes are the mobile or yellow dunes, which as their name suggests are loose
sparsely vegetated dunes that grow and change shape as the wind deposits and erodes sand. The mobile-
dune communities in Britain are dominated by marram grass Ammophila arenaria , which is specially ad-
apted to live in these extremes of temperature and moisture and which grows up vigorously through the
fresh sand deposited on it (Fig. 75).
Other plants of the mobile dunes are sea bindweed, sea spurge Euphorbia paralias , sea holly, a con-
spicuousplantwhichflowersinJulyandAugust(Fig.76),anddunefescue Vulpiafasciculata .Itwasonce
thought that few other plants could survive in this hostile zone. A number of alien plants are, however,
doing extremely well in this zone on the Gower dunes. Probably the most obvious of these is the large
yellow flowered evening primrose Oenothera glazioviana , which now occurs in profusion on Port-Eynon
and Horton dunes, along with fennel Foeniculum vulgare .
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