Coastal Sand Dune Succession

1
Coastal Sand Dune Succession
2
Coastal Dunes

• In a plant free landscape (e.g. after a
  landslide or lava flow, a fresh sandy coastline,
  or derelict industrial wasteland) plants become
  established over a number of years and move from
  the pioneer stage through succession to mature
  climax community of stable vegetation.

3
Remember your terms

• Plant successionchanges in plant community in an
  ecosystem over a period of time.
• Climax vegetationwhen a plant succession has
  reached a balance in vegetation, soil and climate

Often with coastal dune questions part i) will
ask you to define one of these terms.
4
The only such environment that will appear in the
higher exam will be succession across a sand dune
coast.

• A coastal environment is a very harsh
  environment for plants to survive in. As you move
  inland, 200 metres or so from the high water
  mark, you pass through a number of zones.
• You need to be able to
• describe how the physical conditions alter as
  you move inland,
• and explain why the plants have adapted to the
  subtle changes in the environment.

5
Formation of Sand Dunes

• Where there is large supply of dry sand (for
  example, on a sandy beach exposed by the tide and
  heated by the sun), together with winds having a
  speed greater than 15 kph,  the sand will be
  picked up and blown by the wind.
• Plants growing on the shore-line provide mini-
  wind breaks which slow the wind down in their
  immediate vicinity. If the wind is slowed
  sufficiently, it will drop some of its cargo of
  sand. A sand pile will begin to accumulate at
  this point, providing an ever increasing wind
  break. Eventually the sand pile will grow into a
  dune at the back of the beach.

6
With high wind speeds, the sand is continually
pushed over the crest of the dune, falling down
the steeper windward slope. This has the effect
of causing the dune to move steadily inland.
Pioneer plants will begin to colonize the dunes,
gradually holding the sand in one place with
their root networks. New sand dunes may build up
behind the first dune, eventually forming a
series of dunes from the seashore, inland.
7
Stages in succession along a coastal sand dune

• There are 5 main stages in succession across a
  coastal sand dune
• Stage 1 Embryo Dune
• Stage 2 Yellow (Main) Dune
• Stage 3 Semi fixed Dune
• Stage 4 Grey/fixed Dune
• Stage 5 Climax Vegetation

8
Stage 1 Embryo Dune

• Strandline a line of seaweed litter and debris
  along the high tide mark which provides nutrients
  for sea rocket and couch.

9
(No Transcript)
10
Stage 2 Yellow (Main) Dune
As pioneer plants grow they provide shelter for
the thin humus layer which is being formed by the
decomposition of the pioneer biota. The
environment here is still very harsh though, and
only very hardy plants can survive, such as
Marram Grass.
11
(No Transcript)
12
Stage 3 Semi fixed Dune

• At around 10m above sea level, the marram
  grass dies out as the sand supply is reduced,
  meaning a thin humus layer is now permanent and
  soil can form.
• Improved conditions and increased moisture
  content leads to a greater variety of vegetation
  type.

13
A greater variety of plants can now be supported,
including dandelion, ragwort and rest harrow.
14
Stage 4 Grey/fixed Dune

• With the increasing variety of plants, the
  soil becomes deeper and more fertile and can
  support an almost complete covering of
  vegetation. Typical plants Mosses and Lichens,
  Clover and herbs such as Red Fescue.

15
(No Transcript)
16
Stage 5 Climax Vegetation

• When a dune succession reaches its climax
  stage, the vegetation found largely depends on
  the mineral composition of the sand.
• Calcareous (alkaline,shell based)
• rich grassland
• Silica (acidic rock fragments)-
• heath land then deciduous tress

17
(No Transcript)
18
Slacks

• Low lying areas in between dunes (found at
  all stages in the succession). These are often
  marshy due to rise in water table. March species
  develop, along with peat in the waterlogged soil.