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Sand dune succession
A typical succession for the vegetation of the sand dunes can be described
for northwest Europe which potentially includes all the more important successional
communities from strandline (driftline) to yellow and grey dune, dune grassland,
heath and scrub. The description which follows is based on the situation in
the UK:
- Foredune
(yellow dune). The early stages of succession where dune mobility is of over-riding
importance are dominated by marram Ammophila arenaria
and sand couch Elytrigia juncea. In parts
of northern Britain and southern Scandinavia they may occur together; however
Ammophila arenaria tends to be absent further
north. Natura
2000 Codes 16.211 & 16.212 Embryonic shifting dunes and Shifting dunes
with Ammophila arenaria (white dunes);
- Dune grassland.
As a more stable form of dune develops, Ammophila
arenaria becomes less frequent. With decreasing inputs of sand plant
growth diminishes, new shoots are less frequent and the individual culms become
more sparsely dispersed. This process is accelerated under domestic grazing
regimes where red fescue Festuca rubra
and other grasses help form the typical species-rich calcareous dune grassland
when the original sand grains have a high calcium carbonate content. Natura
2000 Codes 16.221-16.227* Fixed dunes with herbaceous vegetation (grey
dune), 1A* Machairs *Priority habitat in Ireland only;
- Acid dune grassland. Sand sedge Carex
arenaria and grey hair-grass Corynephorus
canescens with abundant mosses and lichens are often characteristic
species in an open acid dune grassland, the former species is widespread;
the latter mainly restricted to the East Anglian coast. Possibly Natura
2000 Code 16.24* Eu-atlantic decalcified fixed dunes (Calluno-Ulicetea);
- Dune heath
(brown dune). Crowberry Empetrum nigrum
and heather Calluna vulgaris develop on
dunes where the calcium carbonate content of the soil is absent or low. This
may be due to high silica content and a corresponding lack of shell fragments
in the original dune sand, or from a long period of leaching of the soil surface
in older dunes. Natura
2000 Codes 16.23* Decalcified dunes with Empetrum
nigrum and 16.24* Eu-atlantic decalcified fixed dunes (Calluno-Ulicetea);
- Dune slack.
Dune slacks occur where the water table is near the surface of the sand. They
are found on many dunes and are often rich in species, particularly when associated
with calcareous sand. Some slacks may become dominated by willows (Salix
spp.) together with common reed Phragmites australis
marsh in the wetter areas. Natura
2000 Codes 16.26 Dunes with Salix arenaria
ssp. argentea (Salicion arenariea) and 16.31-16.35 Humid dune slacks;
- Dune scrub. Natura
2000 Code 16.251 Dunes with Hippophae rhamnoides;
- Dune woodland. Because of the extent of grazing very few dunes, if
any, support primary woodland. Secondary woodland with birch Betula
pendula does occur in Scotland. Natura
2000 Code 16.29 Wooded dunes of the Atlantic, Continental & Boreal
region. In northern France dunes can develop towards birch Betula
pubescens woodland with Scots lovage Ligusticum
vulgare (Dargie 2002) and on some
of the larger west coast sites this occurs in a matrix with open eroding dunes.
[Note there are examples of natural pine forests on dunes in a few places
in Europe such as Albania. For a more detailed description of sand dune vegetation
around Europe see (van der Maarel 1993)]
Comment: In areas where beach erosion is occurring some of the early
stages of succession may be absent with the sand dune forming a cliff above
the beach. Alternatively yellow dune vegetation can occur in blow-outs within
the body of the dune. The extent of this will depend on the mobility of the
dune sand itself which helps to define the principle 'states' of the dune.
References
Dargie, T.C.D.
2002.
Ecological Assessment of Hippophae rhamnoides.
English Nature Contract Report, I2.5.2-2
English Nature.
van der Maarel, E.
1993.
Dry Coastal Ecosystems, Polar Regions and Europe. Elsiver, Amsterdam, 600 pp.
Ecosystems of the World, 2A
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