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Sand dunes are divided into different ecological zones
Beaches Foredunes Interdunal wetlands or
toughs Back Dunes or Dune Forests
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Critical factors for sand dune creation: Source of abundant sand Relatively consistent wind Water level fluctuation
dune growth accelerated by high water levels Vegetation to foster sand accumulation
traps and and stabilizes sand
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Sand on the Move! There are three ways wind can move sand:
Suspension Moves the finest grains 1%
Impact creep Moves the heaviest grains 4%
Saltation Moves intermediate grains 95%
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Vegetation to foster sand accumulation Pioneer grasses’ fibrous root systems grow rapidly, binding
sand together and stabilizing the dune
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Pile up! Dune Formation The sand moves until it meets a slight obstruction, such as a clump of grass,
which deflects the wind and allows the sand grains to drop Thus a slight mound or hummock is created Wind moves sand up to the top of the pile until the pile is so steep it collapses
under its own weight and falls down the leeward side called the slip face The collapsing sand comes to rest when it reaches just the right steepness to
keep the dune stable This angle is called the angle of repose and is usually 30-34 degrees
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Migrating dunes
The repeating cycle of sand inching up the windward side to the dune crest and falling down the leeward side allows the dune to inch forward in the direction the wind blows
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BIOSPHERE SUCCESSION
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The beach ends at the strand line. This is the line highest up from the water where the material deposited by the sea is stranded.
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The plants here are tolerant of the harsh conditions- strong winds, sand constantly shifting, salty spray, high alkalinity. There is little evidence of any soil.
Plants here are pioneers;-
sea sandwort
sea rocket
saltwort.
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BIOSPHERE SUCCESSION
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2 Embryo dunes are the smallest hummocks of sand. They create a tiny area of shelter from the on-shore wind. It is here that the first pioneer plant may grow. They are very easily destroyed.
The plants here are only slightly better off than at the strand. They have still to put up with very poor conditions. Soil can only be distinguished using chemical analysis.
Plants here are;-sand couch grass
sea rocket
Lyme grass.
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Embryo and Fore Dunes: the plants
The plants which grow here have adaptations which allow them to grow in a difficult environment :
Sea rocket
• high salt tolerance
• deep tap roots to obtain available moisture Frosted orache
Saltwort
Sea couch
• prostrate (low) habit to avoid strong winds
Sandwort
• waxy leaves to retain moisture and withstand winds
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BIOSPHERE SUCCESSION
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3 Fore dunes are starting to look like proper dunes, though they are still very small. There is an increase in the amount of humus in the sand, and a little less saltiness in the environment.
The plants here are modifying their environment and a wider variety of plants can be found here as a result. Their roots are helping to bind the sand grains together and this allows them to get more water.
Plants here are;-sand sedge grass
Sea holly
Marram grass.
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BIOSPHERE SUCCESSION
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4 Yellow or main dunes are substantial dunes. They can be up to 10m tall. There is a much higher amount of humus, nutrients and it is more acidic. The younger dunes create much more shelter.
The plants here are less tough in many respects, although it is still not a kind environment. Marram grass is the dominant plant, and its long tap roots bind soil and find water deep down.
Plants here are;-sand fescue grass
Ragwort
Marram grass
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Yellow Dunes: the environment
pH 6.5
%OM 0.23
above the level of high
tides
reduced wind speeds
Surface continually blown away and replenished with
fresh sand
‘Soil’ slightly less alkaline and
more water retentive
Some humus forming
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Yellow Dunes: the plants
Salt tolerant Thrives on being buried by sand Inrolled leaves to reduce moisture
loss Long tap roots Underground rhizomes stabilise the
sand
Other plants such as Ragwort, Red fescue and Sand sedge begin to appear
The dominant plant species is Marram grass:
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BIOSPHERE SUCCESSION
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5 Fixed dunes are often called grey dunes. They are lower and more consolidated than the yellow dunes. They have troughs between the ridges of sandy soil- called slacks.
This area supports plants that require more shelter and more acidic conditions. Most need more moisture, and find it in the slacks; more specialist plants appear, like reeds,rushes and creeping willow.
Plants here are;-sand sedge grass
trefoil
Buckthorn
Heather
lichen
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Grey Dunes: the environment
pH 5 - 6
%OM 1.0
sheltered by higher, seaward dunes
lower pH
higher humus content
little mobile sand
sand no longer accumulating
a more closed vegetation community in which
marram grass is no longer able to compete
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Dune Slacks: the environment
pH 4 - 5
%OM 8.5
relief intersects the
water table
water table high – especially in winter
soil acidic
occur in low lying hollows between dune ridges
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BIOSPHERE SUCCESSION
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6 This is the last sere of the plant succession. The land here is damp, sheltered, acidic, rich in nutrients and humus.
The plants here are as evolved as they are going to get- unless man or storms modify their environment again
Plants here are true pioneers;-heathland plants
gorse
Ash, rowan, alder, birch and spruce trees
CLIMAX has been reached !
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Dune Heath/Woodland: the environment
pH 4
% OM 12.1
well sheltered from winds
acidic soil
nutrient rich
maritime influence is minimal
soil has high organic matter content
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