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State 3 - Overgrown or afforested 'fixed' dune
The 'fixed' dune state can be recognised in two forms:
- Overgrown - where the amount of bare sand and/or open low-growing
vegetation is reduced or disappears altogether as scrub and woodland
develops. This state typically occurs where the natural tendency of
sand dunes to progress to scrub and woodland has been hastened by a
variety of techniques designed to prevent erosion including fencing
and Ammophila planting. As the vegetation becomes more stable
there is a corresponding loss, eventually of all of the open dune communities
and most of their associated species and with it a reduction in its
nature conservation value.
In the most stable situations these can become rapidly overgrown and
invaded by birch (see picture opposite), Hippophae
or self sown pine;
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Caption:
Tentsmuir, Fife Region, east Scotland October 1983. Note the 2nd World War
tank traps built in a dune slack, now surrounded by invading birch.
- Afforested - this state is frequently found on dunes throughout
Europe. Historically the specter of eroding dunes elicited a common
response, prevention of the destabilising vector (such as cutting Ammophila
for thatching and animal bedding, in the case of the Sefton
Coast by Act of Parliament in 1742), planting of Ammophila
and afforestation.
In the 19th century large scale sand movement was prevalent along most
of the 230km of the Acquitaine
coast which also resulted in major stabilisation. It results in the
loss of open dune vegetation and its replacement by dense stands, usually
of various species of pine. Although this causes a loss of nature conservation
value,
other interests can be identified.
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Caveat: Although not recognised specifically as a type
of dune a fourth state can be recognised in areas where agriculture use has
resulted in the dune topography being destroyed to create land suitable for
crop cultivation. In some areas the only evidence of the former dune habitat
lies in the sandy nature of the soils. Extensive areas of the Netherlands, particularly
the bulb growing fields, have been developed in this way. The Machair
of Scotland and Ireland is a special form of this type of management, but where
the formation has derived a high nature conservation value by virtue of the
long and sustained low input agriculture which has been practiced there. Restoring
dune vegetation in these areas is an option which could include allowing eroding
dunes to 'roll over' under the influence of increasing storms and/or sea level
rise.
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