1 sand dune succession. 2 sand dunes are divided into different ecological zones beaches foredunes...

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Sand Dune Succession

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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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Sand dunes follow a set layout.

Copy this diagram to act as a key for your notes.

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An aerial view of a sand dune system

youngest dunes

oldest dunes

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A transect across a sand dune system

X Y

Reveals variations in relief and vegetation ………..

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X Y

A transect across a sand dune system

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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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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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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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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

Click on photo to reveal annotations

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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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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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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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1 sand dune succession. 2 sand dunes are divided into different ecological zones beaches foredunes...

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