|
|
|
|
|
|
|
|
|
|
|
The
Australian Arid Zone contains the most spectacular and largest longitudinal
dune systems in the world. The first dune systems were created during arid
and windy glacials around 900,000 years ago in the Lake Amadeus region in
Central Australia. Because these cycles of glacial and interglacial were
repeated, it is very difficult to determine the exact age of sand dune deserts.
Thermo luminescence has been used to determine the age of sand dune particles.
Core samples in the Simpson Desert taken by the University of Woollongong
suggest it is only around 20,000 years old. Present theory suggests most
of the current dune systems in Australia were formed by a dominating sub
tropical anti cyclonic air system which has prevailed over the Australian
continent for the past 20 to 30,000 years, continually picking up dust and
sand from depot centers and depositing it as vast longitudinal dunes, some
over 100kms in length. This geological process is akin to a living-breathing
organism. Lake Eyre becomes the heart. The great rivers flood, carrying
silt down into this vast holding pan, where it is picked up and carried
by the wind into the Simpson Desert. Likewise, the Macdonnell Ranges, once
the size of the Rockies have eroded down to form the sands of the red center.
|
|
|
|
|
|
|
|
 |
|
Vegetation
The vegetation varies from desert to desert, however there are some commonalities.
There are several vegetation groups and micro ecologies within sand dune
systems. The longitudinal dunes support an entirely different vegetation
to that of the interdunal corridors or swales. The most common plant groups
in the Simpson, Tirari, Strezlecki and Great Victoria dune fields are
Chenopodiaceae (saltbushes), Compositae (daisys and composites) and Graminae
(grasses).
The tops of the ridges are demobilised by binding plants such as sandhill
canegrass (Zygochloa paradox). This extraordinary plant is a perennial
grass that sprouts from the root, generally during warm summer periods
of rainfall. The new growth dies off quickly, however it continues to
play a binding role. Observed patches of "dead" canegrass has
continued to bind sand hills in Western New South Wales for over 20 years. Canegrass
is both ubiquitous and beautiful. As the heat goes from the day, and the
burning light of the sun disappears behind Simpson Desert dune crests,
the eastern faces of the dunes in shadow are stunning, the driftwood blue
of the clumps of canegrass contrasting with the reds and oranges of the
desert sands.
Triodia (Spinifex) is the other dominant grass in the dunefields of Australia.
It tends to grow in the swales and on the dune faces, but not on the ridges.
It is also not seen in saline or clay based soil areas. This is dealt
with in detail in the section on Spinifex. These two plants are what botanist
on the Madigan Expedition - Robert Crocker was to describe as, "present
throughout with remarkable homogeneity."
In the Simpson, Tirari and Strzelecki deserts, acacia bushes and trees
are prevalent on the dune faces and in the swales, however they rarely
appear on the crests, aside from the sandhill wattle (acacia dictyophleba).
The umbrella bush (acacia ligulata) is very common on the dune slopes
and in the swales. By digging around this plant and identifying it's swollen
roots, one can find fat witchetty grubs, once an important Aboriginal
food source. Another common acacia bush is the Elegant Wattle (acacia
victoriae), with it's gnarled bark, singularly unattractive foliage and
absolutely stunning and showy creamy blossoms. As well as this is Dead
Finish (acacia tetragonophylla) the last plant to survive in the drought.
On the eastern and northern sides of the Simpson Desert are the beautiful
Gidgee (acacia georginae). Whilst the foliage of this plant is generally
poisonous, traveling through gidgee swales is like gliding through ancient
olive groves, the plants en masse contrast with the red sand with a stunning
aqua colour. The scent given off by their volatile oil when wet or humid
is considered by some to smell like cat's piss. I call it eau d' gidgee,
and it must be an acquired taste, because the longer I spend in the desert
the more it appeals to me. There is also the ubiquitous Mulga (acacia
aneura), predominately in it's sandhill form, which is dealt with in detail
on the Mulga Shrublands page. Myrtaceae (eucalypts) are not seen in the
Simpson except along river lines and floodplains on the deserts edge.
Hakea and Grevillea are also represented in all the Australian deserts.
Grevilleas have stunning flowers that drip with pollen, often providing
food sources for Aboriginal people. One of the most sensual and exotic
cullinary experiences is to wrap your lips around the blossom of a golden
Honey Grevillea (grevillea eriostachya).
In the dunefields of the Great Victoria Desert you will see the
large eucalypt Marble Gum (Eucalyptus gongylocarpa) growing in sandy soils,
even on the dune crests. The marble gum grows up to 20 meters high. Tall
trees in dunefields are perhaps the most striking differences between
the western and northern dunefields and their southern and eastern cousins.
There are also many different types of Mallee, such as the Ooldea Mallee
(Eucalptus youngiana) and the Kingsmill Mallee (Eucalyptus kingsmillii)
with their strikingly beautiful large flowers.There are also open woodland
communitys of Black Oak (Casuarina pauper), and the native pine (Callitris
verrucosa).
In the Great Sandy and Little Sandy Deserts of the northwest, spinifex
is the most common plant. There are also a number of eucalypts represented,
notably the snappy gums (Eucalyptus brevifloai and leucopholia), the white
stemmed ghost gums(E.papuana) as well as numerous others. There is the
exotic Desert Walnut(Owenia reticulata) and several native figs.
Grevillea and Hakea are well represented, as well as cassias and a myriad
of small flowering plants. One plant which often outcompetes spinifex
in the northern and western deserts is Desert thryptomene (thryptomene
maisonneuvii) with its beautiful white and pink flowers. It smells of
sweet plasticine.
|
|
|
|