The Physical Core
Biosphere
Plant Succession
:Psammoseres
Important
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Plants are the key to the formation and
character of sand dunes. If there were
no plants and no plant colonisation,
there would be no sand dunes.
For pioneer plants however there are
several obstacles to overcome
Obstacles for pioneer species
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Strong stormy high tides and the use of
beaches by people can destroy plants and
dunes.
Sand is a sterile environment often lacking
humus and nutrients.
Sand can be very dry due to the rapid
drainage. Drought resistant plants are
classified as xerophytic.
Shelly fragments often create an alkaline
environment.
Model Sand Dune
Embryo, fore and mobile dunes
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Plants that occupy this area of a sand
dune have to be xerophytic.
They also have to have particular
growth features.
Be resistant to salt water
during spring tides
Have foliage to trap the
sand, causing it to drift
over them.
As they grow vertically and laterally, they bind the sand
and build up embryo and foredunes.
Sea rocket, sea lyme and couch grass
Couch grass
Sea rocket
Sea lyme
Yellow Dune
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Once the tops of dunes have grown well above
the highest tide level, marram grass is able
to colonise.
This is the main pioneering plant.
Thanks to rhyzomes (long creeping
underground roots) spreading vertically and
laterally, the marram very effectively grows
with fresh deposits of sand.
Marram Grass
Marram Grass
Grey dunes
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On the landward more sheltered side of dunes
more plant species establish themselves.
Such fixed dunes are called grey dunes
because of the increased humus content of
the soil and the surface growth of lichens.
As the distance from the shore increases,
sand no longer accumulates and marram grass
cannot compete with new colonising plants.
Sand sedge, buttercups & dandelions.
Sand sedge
dandelions
buttercups
Older grey dunes
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Further inland, the older grey dunes
support bushes such as sea blackthorn
but more ‘ordinary’ plants are also
present – gorse, broom, heather.
One factor is that the soil is now more
acidic. Any lime from the shells has
been leached (washed out) and the
amount of humus is now greater.
heather
broom
Dune Slacks
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Other ‘ordinary’ species occupy the
dune slacks. These damp, low lying
hollows have a higher water table,
especially in winter.
Hydrophytic (water tolerant) vegetation
thrives: rushes, willows and alders are
found here.