This page is an extract of a script that
is part of the video series
"The Living Landscape-an Australian Ecosystems Series".
Visit all ecosystems.
LARGE MULGA
TREE
Mulga is a low shrub of stunted
acacia, that grows in relatively infertile clay soils. Mulga is hardy: some
species can live for up to 200 years. But to do this, mulga relies on seedling
regeneration, and it needs three heavy rainfalls to regenerate.
Mulga needs rain in summer, winter, and the following summer: a sequence that, in arid areas, occurs only about once every ten years. Mulga, however, is threatened by rabbits, and by stock. After a heavy rain sequence, mulga isn't the only thing that increases. Other plants also grow, and rabbit numbers increase.
EUROPEAN
RABBIT
Rabbits do tremendous damage.
During great plagues of the past, they stripped the landscape, killing even
mature trees by eating the bark.
ARID INLAND
- AERIAL VIEW
Arid and semi-arid regions appear
sparsely populated, but they're home to a variety of native animals that
have evolved to survive the harsh conditions.
RED KANGAROO
Kangaroos, for example, reduce water
loss by feeding at night and resting in the shade during the hottest part
of the day. They're able to travel great distances in search for food and
water.
BREEDING
AUSTRALIAN PELICANS
Even wider-ranging travelers are
birds like pelicans. When conditions are right, after good rains, inland
lakes and rivers fill up. This doesn't happen often, but when it does, thousands
of birds flock into the inland to breed and feed. In 1992 there were exceptionally
good rains. Water covered Lake Eyre, for only the third time in 200 years.
The pelicans flocked in. Soon, there were 50 000 of them nesting on islands
in the lake. Pelicans are big birds. They can weigh up to 9 kg, and have
a wingspan of up to two metres. It seems incredible that so many found food
in central Australia. But it was possible.
With the rains, the environment had boomed.
Microscopic plants grew in the warm lake water. Equally small animals fed
on the algae, and they, in turn, fed water insects and tiny crustaceans.
Fish fed on the insects and crustaceans - and the pelicans fed on the fish.
Later in the year, however, the party was over. The lake was drying up.
Many birds died. Those who were strong enough left the drying lake, flying
sometimes thousands of kilometres to find permanent water elsewhere.
BILBY See
New Bilby page including streaming video
HERE
But animals that can't travel have to
find different methods of survival. Most desert animals shelter by day and feed
at night, and many stay cool by going underground. It may be appallingly hot
on the surface, but even just half a metre underground, it can be much cooler.
A bilby's burrow, for example, between one and two metres deep, can be as much
as 10 degrees cooler than the surface temperature. The air in a burrow is moister,
as well, so the bilby loses much less water. Bilbies actually get most of their
moisture from their food: termites, insects, bulbs, roots and seeds. Even a
clump of spinifex provides a surprising amount of protection from the sun for
animals.
SPINIFEX
Spinifex has also evolved to survive
in this harsh climate. Its leave are hard and sharp, folded into tight cylinders.
Spinifex leaves start out flat, but if the plant is stressed the leaves
fold and become almost cylindrical. This reduces the surface area, which
slows down the rate of heating and water loss, and assists in sheltering
some of the pores - thus reducing water loss still further. Spinifex roots
also spread out deep and wide, to pick up both ground water and surface
water. Around the base of the clump, there'll be hundreds of small seeds,
waiting for the rain, and a chance to germinate.
Similarly, the grey mulga has evolved to thrive in this harsh climate. An individual tree is shaped like a funnel. When rains come, the water is caught by the foliage and runs down the branches into the centre. It ends up at the base of the tree, soaking into the soil near the roots.