Grasslands of the World.pdf - Disasters and Conflicts - UNEP

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Grasslands of the world
grazing but these have been supplemented – and in some cases replaced – by
exotic species.
There are a number of descriptions of Australian grasslands (e.g. McTaggart,
1936; Moore, 1970, 1993; Groves and Williams, 1981) that have been drawn
on in preparing this paper. Following Moore (1970), all herbaceous communities
used for livestock production are considered grasslands, and include both
native communities that are grazed and pastures composed of mainly introduced
plants, either sown or volunteer. This paper concentrates on dryland or
rainfed pastures, but irrigated pastures are important (approximately one million
hectares), particularly in some dairying areas in southern Australia (about
half of all irrigation water in Australia is used on pastures).
LOCATION
Australia covers an area of 7.68 million km 2 , from 11°S to 44°S, and this
latitudinal range, coupled with annual rainfalls ranging from 100 mm to more
than 4 000 mm, both coastal and inland areas, and a variety of soils, generates a
wide range of grassland environments.
PHYSICAL FEATURES
The Australian landscape is characterized by vast plains and plateaux (threequarters
lie between 180 and 460 m above sea level) with only limited elevated
areas. The continent can be divided into three major structural components –
the stable Western Shield, the gently warped Central Basin, and the Eastern
Uplands (from Tasmania to north Queensland), which are of ancient origin
but have been rejuvenated to some degree. These components determine
the pattern of relief and drainage. The Eastern Uplands contain the highest
mountains in Australia (including Mt Kosciusko, 2 200 m) and the only area
with snow. They form the divide between the steep eastern-flowing rivers and
those draining west. The Central Basin has two major drainage systems – the
Murray-Darling system, which includes runoff from the southeastern rim, and
one draining internally to Lake Eyre. The Great Artesian Basin lies to the west
of the Eastern Uplands in Queensland, New South Wales and South Australia,
and water from this Basin has enabled grazing industries to establish and
persist over a wide area of arid and semi -arid inland Australia.
CLIMATE
Rainfall
Total annual precipitation varies from more than 4 000 mm in the mountainous
areas of northeast Queensland to approximately 100 mm in the north of
South Australia . Approximately one-third of Australia receives over 500 mm
of rain, one-third has 250 to 500 mm and one-third has less than 250 mm;
rainfall is greatest in coastal areas and lower inland. Seasonal distribution varies
markedly over the continent, from strong summer dominance in the north