Sand Dunes
[Date]
Today I will:
- Look at a transect across sand dunes to see
what the differences are.
Geography
Biosphere
X
Y
Geography
Biosphere
Pioneer Stages: The first plants
to colonize an area are called the
pioneer community. They add
humus, nutrients and water and
therefore improve the soil.
Geography
Biosphere
Succession Stages: The improved soil begins to attract
larger species. The number of species and height of plants
increase.
Geography
Biosphere
Climax Vegetation: This is the final stage in succession when the ultimate
vegetation has developed. The type of vegetation is mainly dependant on
the climate.
Geography
Biosphere
What is Climax Vegetation? [8marks]
Climax vegetation is the final stage in the development of the natural vegetation in
any given region [1]. Plant communities will change as environmental conditions
change [1]. Hardy pioneer species will colonize an area first [1]. As they die out they
add humus to the soil, allowing other plants to grow and survive – this is known as
succession [1] . When this happens, the composition of the plant community is
relatively stable and in equilibrium with the existing environmental surroundings
(normally the soil or climate) [2]. When climax vegetation has been reached plants
are well established and trees such as pine and birch can be found [2]. Biomass is
also at its maximum [1].
Equilibrium: In balance or the
same as.
Biomass is biological material
derived from living, or recently
living organisms.
Geography
Biosphere
Read pages 165 to “Introducing Soils” on page 168 and answer the following
questions.
1. What are the three necessary requirements for the development of a sand dune
system?
2. Why is it so difficult for plants to grow on sand dunes?
3. How has marram grass adapted to the difficult conditions on the Yellow Dune?
4. Define the following terms:
[a] Xerophytic
[d] Rhyzomes
[b] Colonising
[e] Hydrophytic
[c] Saltation
[f] Psammosere
Geography
Biosphere
This is a cross section view of the dunes. On your piece of A3 paper draw
out the cross section neatly.
You should notice that there is a change in relief and the vegetation
Geography
Embryo and Fore Dunes: the environment
Biosphere
On-shore winds
High water mark
Poor water retention
Sand builds up against
pioneer plants
Seaweed
deposits
humus
Transient dunes
Sand alkaline
Geography
Biosphere
The Strandline
Sandwort
Sea rocket
Strandline - Sea Sandwort; Sea Rocket;
These are all salt-tolerant (halophitic) species. They are low in height and have waxy leaves to
withstand the wind and retain moisture. Some can even withstand periodic immersion in sea water.
The presence of these plants leads to the further deposition of sand by trapping the sand. The high
pH figures can be attributed to a high concentration of shell fragments. (CaCO3).
Geography
Biosphere
Embryo Dunes
Lyme grass
Sea couch
Embryo Dune - Sea/Sand Couch; Lyme Grass:
These dune pioneer species grow side roots and underground stems which bind the sand together.
These grassy plants too, can tolerate occasional immersion in sea water and a low humus content.
Some species found on the strandline are also found on the embryo dunes (Sea Rocket).
Geography
Biosphere
Fore Dunes
Sea Bindweed
Sea Holly
Fore Dunes - Sea Bindweed; Sea Holly;
A slightly higher humus content (from decayed plants), and lower salt content (further
from the sea) allows these species to further stabilise the dune and allow the
colonisation of Marram Grass which becomes a key plant in the build up of the dune.
Geography
Biosphere
Yellow Dunes
Above the level of
high tides
Reduced wind
speeds
‘Soil’ slightly less
alkaline and more water
retentive
Some humus
forming
Surface continually blown
away and replenished with
fresh sand
Geography
Biosphere
Yellow Dunes
Marram Grass
Yellow Dune – Marram Grass:
Both the humus content and the acidity of the soil have increased at this location. Marram can align
itself with the prevailing wind to reduce moisture loss; it can also survive being buried by the shifting
sand of the dune. In fact, as sand deposition increases the Marram responds by more rapid growth (up
to a staggering 1 metre a year). It is better able to survive the dry conditions of the dune than other
plants. This allows it to become the dominant species on the Yellow Dune. It also has long roots which
help to bind deposited sand and anchor it into the dunes as well as access water supplies some
distance below.
Geography
Biosphere
Dune Slacks
Occur in low lying hollows between dune ridges
Soil acidic
Relief intersects the
water table
Water table high –
especially in winter
Geography
Biosphere
Grey Dunes and Slacks
Sand Sedge
Sand Fescue
Grey Dunes and Slacks - Sand Sedge; Sand Fescue;
As a result of an increase in organic content (humus), greater shelter and a damper soil
a wider range of plants can thrive here. Marram dies back (contributing humus) to be
replaced by other grasses, sand fescue and sand sedge. As a result of leaching and the
build up of humus the soil is considerably more acidic again supporting a wider plant
community. In the wetter slacks, close to the water table, several water-loving
(hydrophytic) species may survive.
Geography
Biosphere
Climax Vegetation
Birch
Pine
Climax Vegetation – Birch, Pine:
Eventually trees such as birch, pine or spruce could establish a foothold. Here
the ecosystem has reached a dynamic equilibrium.