Geoscience Reference
In-Depth Information
were soldiers or convicts, came from Britain and Ireland and were imbued with
methods of farming adapted to those temperate and well-watered lands but poorly
suited to the inherently infertile soils and highly variable rainfall regime characteristic
of much of Australia. In their efforts to recreate the 'green and pleasant land' they
had left, the first Anglo-Celtic farmers set about clearing the woodlands and forests
with enormous energy and efficacy - a tradition that continues to this day, despite its
destructive impact. In
A Land Half Won
, historian Geoffrey Blainey describes a scene
at a farm in Gippsland, Victoria, about 150 years ago. The dying farmer summons his
sons, points proudly to the total lack of trees where once stood forest and declares
that he can now die content, his work well-done (Blainey,
1980
).
It is easy to stand in judgement on the tree clearing activities of the early Anglo-
Celtic settlers in Australia, but doing so has the wisdom of hindsight. The first
European farmers probably had no idea of the adverse long-term effects of clearing
the deep-rooted eucalyptus trees. The Polish-born geographer, naturalist and explorer,
Paul de Strzelecki (1797-1873), who named Australia's highest mountain, Mount
Kosciusko, and after whom is named one of Australia's sand deserts, the Strzelecki
Desert, was a perceptive early observer of accelerated soil erosion, warning against the
adverse effects of clearing and burning on soil organic matter, soil structure, infiltration
capacity and soil erosion (Strzelecki,
1845
). However, even a man as observant and
well-informed as Strzelecki did not realise that the eucalypts functioned as natural
groundwater pumps and prevented the groundwater from rising as far as the rooting
zone of shallow-rooted cereal crops such as wheat and barley, bringing dissolved salts
to the surface in a process now known as
dryland salinization
(Macumber,
1991
;
Williams,
2000
a; Lawrie and Williams,
2004
). Under native vegetation, groundwater
recharge in the Murray-Darling basin of south-east Australia amounts to a mere 1-
2 mm/year, as opposed to 40-140 mm/year under wheat cultivation. Once the land
was cleared, the groundwater levels rose, slowly but inexorably, bringing dissolved
salts to the surface. There are 10
11
tons of salt in the groundwater of the Murray
Basin, and about 1.5 million tons of new salt are deposited into the Murray-Darling
catchment each year from rainfall (Herczeg et al.,
2001
).
The loss of woodland and forest is not always easy to gauge, but best current
estimates are that half of the original woodland and forest that grew in Australia
200 years ago are gone. Government policies aggravated the problem, because until
quite recently, farmers were required by law to clear a certain area of their land
each year or else forfeit tenure of the land. Sadly, the orgy of deforestation has not
yet abated, and inconsistent and feebly enforced State policies offer little solace. In
the ten years before 1993, Australia cleared an average of 500,000 ha of woodland
and scrub each year, which some observers in this nation of sport enthusiasts have
expressed as equivalent to two football pitches per minute. (The area of a standard
football pitch is about 9,000 m
2
and that of an Australian Rules football playing
field is about 20,250 m
2
, so such comparisons are suggestive rather than precise, but
