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When Antarctica separated
from Australia the South-West coast uplifted several times causing
changes in the sea level.
Approx 40mya a sea covered much of the
South-West which was rich in marine organisms.
In the last 2 million years
(the Pleistocene period) polar icecaps have contracted and expanded many
times, making the sea level rise and fall repeatedly. 18,000
years ago the land was formed out past Rottnest Island to the
west. 7000 years ago the land had retracted but
you could still walk to Rottnest. By 5,000 years ago Rottnest
was cut off from the mainland. With changing coast line comes sand
dunes that formed into limestone reefs and cliffs that are still seen on
the South-West coastline today called the Tamala Limestone. |
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Today the South-West has the
Indian Ocean to the west and the Southern Ocean to the south. The
south-west goes from around Shark Bay in the north to Isrealite Bay in the south.
Over 80% of WA's human population lives in the South-West.
In the south of the South-West
around Cape Naturaliste-Leeuwin is granite basement rock with limestone
on top.
In the southern areas of the Cape Naturalisete-Leeuwing block the
limestone has weathered to form the Yallingup-Augusta cave
systems.
In the southern coastal plain are river floodplains, inlets and
sandy beaches separated by granite cliffs.
The Porongorups are composed of granite.
The Nullabor plain is on top of limestone and extensive caves are in
this area.
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What's
the weather got to do with it?
Climate is one of the most important
components in the ecosystems of the South-West.
It has direct control on all life forms and can change landforms.
The soil that develops on top is determined by the rainfall, wind and
temperature.
Over the last 4 million years the climate was monsoonal in the
south-west. Now the climate is Mediterranean.
Rainfall dictates if seeds will germinate and the structure and height of the vegetation.
In the southern
hemisphere the high pressure systems (anticyclones) have air circulating
in an anti-clockwise direction and bring dry weather, while low pressure
systems have clockwise winds and bring rain.
In summer there are high temperatures and heat waves. In winter
the temperatures drop an average of 15 degrees.
The highest rainfall areas in the South-West are along the extreme south
and south-west coasts and in the Darling Scarp. The amount of
winter rainfall varies around the south-west. Also the
reliability of the rainfall varies around the south-west. Droughts
are common in the interior.
In the north the climate is
more arid and the bedrock is mostly sandstone.
The Nullabor has low rainfall.
Some plants such as Karri trees and some orchids only grow in the cooler
regions. Many other plants are determined by the weather as to
where they can grow.
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Soils of the South-West The
same factors that control weathering control soil formation with the
exception, that soils also requires the input of organic material as
some form of Carbon. The soils are essential for plants
and insects which in turn
native animals are reliant on for food, shelter, nesting, cover from predators
etc.
Soils have both weathered rock e.g. quartz sand; and plant and animal
material. Because
there are different base rocks around the South-West there is also a
variety of soils.
There is only a thin layer of soil on the Earth's crust in the
south-west
and they have a low phosphorus, potassium and nitrogen content which
make them generally quite infertile.
There are five basic soil
components in the south-west; Pea gravel or duricrust, clay, sand, rock
fragments and organic matter. They have formed under different
conditions and support different plants.
Quartz sand can hold
significant amounts of water, peat acts like a sponge filled with water
and clay rich soils also hold water such as clay pans. In summer
under very hot weather conditions when the water evaporates these soils
can stay cooler just a few centimetres below the surface which
allows seeds and tubers etc to survive until the next rains.
In humid tropical climates intense weathering involving leaching occurs,
leaving behind a soil rich in Fe and Al oxides, and giving the soil a
deep red color. This extremely leached soil is called a laterite.
Inland the sands are rich in iron which
gives the soil/sand its red colour. But the soil is infertile and
drier than the soils in the west of the South-West. In arid
climates the amount of water passing through the soil is not
enough to completely dissolve the different minerals.
Go
to our Darling Range, fault, scarp and plateau page to learn
about this area.
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Flora or Vegetation of the
South-West
This is not intended to be a
complete list of flora or plant distributions. Go to our Flora
of Western Australia pages to see a lot more flora from all over
Western Australia.
The South-West is one of the
richest flora areas of the world. There are more than 4,000 species of plants in the South-West. About 70%-80% of the flora in the
South-West is endemic, that is native and restricted to that area. There are more
species of plants in the South-West than in the rest of the whole
state. The South-West is only 15% of the landmass of Western
Australia.
The natural flora or
vegetation will depend on land formation, climate conditions and the soils.
The trees are broad leafed and
evergreen (they don't drop their leaves in Autumn).
Why does a place that has
such infertile soil support so many plant species? Its thought
that due to the lack of nutrients in the soils of the south-west that
this restricts any one plant becoming dominant and taking over.
The poor nutrients act as a barrier from mass plant reproduction.
This allows for diversity of species not only for the plants but for the
wildlife that relies on this variety of plants.
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Forests
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lower South-West and
south coasts have wet sclerophyll (hard leaf) forests
dominated by karri from south of Nannup through to Denmark on
the south coast, where rainfall is greater than 1100mm per
year. It can also be found near Margaret River,
Albany, Mount Manypeaks and Porongurup Range.
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The best specimens of Karri are found on
granite based earth with deep red clay loam soils. Marri will also grow here to greater heights
than it will in the
drier arid regions to the east.
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These forest trees have
deep long tap roots that reach underground water in dry hot
summers.
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Tingle grows in the
karri forests and is now restricted to the Walpole-Nornalup
area in the whole world.
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The Karri Sheoak tree
grows in these karri forests also.
This is the base of an ancient
tingle tree.
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karri tree Leeuwin
National Park south Margaret River
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There is also
dry sclerophyll forests dominated by jarrah, and tuart forests
to the north-northeast of the karri forests going along the
narrow Darling scarp to the Stirling Range and north of the
Blackwood river. Jarrah
thrives on the laterite soils that gets over 600mm of rain per
year. In a jarrah forest is marri, blackbutt,
silvery-barked bullich, woodypear, upright snottygobble and wandoo on the forests edge. It
has a rich ground storey of many shrub species
such as she-aok, bull banksia, parrot bush, grass trees,
zambia palms etc.
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The jarrah tree can pump up with its
long tap root 200 litres of water per day.
An old hollowed out
large jarrah tree, Nanga.
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Tuart Tree from the
Tuart forest near Busselton
Marri is widespread
from the Murchison River to the South Coast and east to Cape
Riche.
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Woodlands
The main woodland area
of the South-West is located east of the dry sclerophyll forest in
the western wheatbelt in valleys of the Darling Plateau area. In this area there are a number
of Wandoo trees along with Salmon gums, york gum, morell, yate and
mallet and in the dry east the dominant vegetation is mallee.
The soils are sandy and gravelly. The understorey of shrubs are grevilla,
wattle, olearia, cassia, phebalium and templetonia.
Banksia is found north
of Perth in sandy soils and in jarrah forests.
The Red-flowering gum is found in other banksia and eucalypt woodlands
and is found near Mount Frankland to Walpole and east to Denmark.
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Wandoo at Julimar
National Park northeast of Perth
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Orange Wattle
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The semi parasitic Christmas tree
with its bold orange flowers lives in woodlands and the coastal plain from
Kalbarri in the north to Israelite Bay in the south and inland to near
Kellerberrin.
Orange Wattle grows in woodland and
through the south-west forests and coastal plain.
The yate tree grows in woodlands
and forests around granite outcrops and is found from Bussleton in the north
of its range to the Stirling Range.
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Shrubland
The flat sandy area of the north, interior and south-east of the South-West have a variety of
shrubland flora. This soil is sandier, drier and
infertile where the water evaporates or soaks away to quickly to support
trees. The shrubs are over 2m in height. The root system of these
plants are shallow to absorb the water before it evaporates.
The karri wattle is a shrub of the
Karri forest and occasionally in the southern jarrah forest and swampy areas
near the South coast. It is found between Nannup and Denmark as far
north as Mount Roe.
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Heath
(scrub)/Kwongan
Rainfall is between
250-400mm a year.
The heath or
scrub is between 1-2m in height.
The south-east coast is dominated by mallee heath and the
nullarbor region has low scrub and poor seasonal grasslands.
In the north coastal area is acacia scrub, melaleuca's, hakea,
grevillea and in deep sandy areas there are banksia's.
Kalbarri, Stirling Range and Fitzgerald River National Parks and
Mount Lesueur near Jurien are rich flora areas.
We have not covered all the low bushes, ground covers, orchids and
wildflowers here on this page due to space. See our Flora of
Western Australia pages.
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Swamps
Swamp paperbarks,
she-oaks, flooded gums, wattie, swamp peppermint and
tea-trees grow in swampy soils around rivers and saltlakes with
sedges growing along the banks. The bullich tree grows near swamps
or granite outcrops scattered through forests and coastal heaths
from near Perth to Albany and the Stirling Range.
Swan River Blackbutt
grows around rivers on loamy soils or major valleys, creeks and
sandy depressions from east of Perth to Albany.
The flooded gum grows
along watercourses and swamps from Eneabba to Margaret River and
east to Pallinup River.
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Swamp Paperbark
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Wildlife
or Fauna of the South-West
You can go to our other pages
on Fossils to see what wildlife or fauna was here in Western Australia
through WA's past. Also visit our Hotspot pages as here you
will see the wildlife and places that we have seen somewhere in
this unique large state of ours. Now,
today, there is still a large variety of species living in this hot Mediterranean
climate, with poor nutritional soils. The vegetation can be spiky
and sparse due to land clearing
and introduced animals; the leaves are high in oils and tough
to digest along with the introduced predators such as the fox and feral
cats. Despite this there is still a high number of marsupials, reptiles, birds,
insects and many frog species throughout the state. But we have to
remember that those animals that couldn't adapt are no longer here now,
those that can have remained. Some of our wildlife just didn't
have a chance! Australia has been isolated for a long time and
introduced pest species both of plants and animals are very
recent. We haven't seen the full impact that these introduced
pests and land clearing will eventually cause this state. Marsupials
have a very low water requirement. They get most of their water from
what they eat. Reptiles generally don't drink water although they
may absorb it through their skin when they find a puddle.
Nocturnal animals reduce their need for water by being active in the
cooler nights. Kangaroo's lick their forearms when they are hot
and some have adapted to drinking very little water or salty water such
as the Euro's at Cape Range National Park.
And most wildlife avoids the heat of the midday sun feeding mostly in
the morning and late afternoons.
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approx 96 species of mammals
including marsupials live in Western Australia, excluding marine mammals,
and there are 37 species of bats.
300 bird species live in the South-West
over 420 reptile species excluding marine turtles and sea snakes live in
Western Australia.
Approx 78 species of frogs live in Western Australia.
I don't know if the individual insect species have been counted for WA,
and of course there are a lot of termites and introduced flies.
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There is a direct
relationship between the landforms the climate, the plants that live
here
and the wildlife that lives within an area. The rainfall, wind
and heat shapes the land. The land provides vital habitat for
wildlife and a base and minerals for vegetation to grow. Which in
turn insects eat and live in which in turn provides food both as the
plants and the insects to other wildlife, which some in turn become food
for other wildlife and so it goes on until the animal waste, dead plant matter and
animals become food again for the living via fungi that help to break
down and extract the nutrients to give back to the vegetation. So
even in this infertile hot place has amazing wildlife, flora and fungi! |
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Text;
Geology and Landforms of the
South-West by Lain Copp
Landscapes and Land Uses Studies in Australian Geography by Diane Guy,
Joe Kalajzich and John Nelson
Wildflowers of Southern Western Australia by Margaret G Corrick and
Bruce A Fuhrer
Common Trees of the South-West Forests by Judy Wheeler
The Living West
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