Environmental Engineering Reference
In-Depth Information
centre of Swansea and hectares of blackened common were the result. Although burning is now less pre-
valent, it continues to this day and still causes problems. Part of the reason is the large area of the com-
mons characterised by purple moor-grass and gorse, habitats that are traditionally burnt to improve the
grazing. While some burning can be beneficial to heathland, on most of the commons it is still carried
out too frequently and when it is combined with heavy grazing it results in a loss of heather. In Gower it
especially encourages the spread of bracken, particularly when it temporarily reduces competition from
heather. Burning is particularly damaging to invertebrates and lower plants, which often only survive on
rocky outcrops where they are protected from the flames. The damage caused depends partly on how dry
the underlying soil is. If the ground is wet the fire tends to be superficial, but if the ground is dry a severe
'deep burn' can result, which destroys both the seed bank and the roots of plants. The fact that many of
the commons contain wet heath means that the fires are not as damaging as they otherwise might be. In
many cases, however, the frequency of burning is such that it is still damaging and in general the activity
is having considerable effects on the wet heath communities, despite the efforts of conservation organisa-
tions.
FIG
124.
Burning on Cefn Bryn Common. (Harold Grenfell)
On some of the commons, particularly Cefn Bryn, rhododendron, an invasive non-native plant, is en-
croaching rapidly adjacent to woodlands where it was originally planted for game cover. Rhododendron
was first introduced in the late eighteenth century, probably from Spain or Portugal. It became especially
popularoncountryestatesinVictoriantimes,providingornamentalvalueaswellascoverforgamebirds.
Rhododendron thrives in milder, wet climatic conditions, where there are poor, acidic soils, and is there-
fore unfortunately well suited to the Gower commons. Unless established stands are constantly kept in
check they expand into adjacent areas, rapidly eliminating the majority of native plant species.
Rhododendron seeds are tiny and dispersed by wind, and a large bush can produce several million
seeds per year. Seedlings have difficulty becoming established in areas where there is already continuous
