1370.0 - Measuring Australia's Progress, 2002
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 19/06/2002
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Agriculture is the major form of land use in Australia. In 2000, 59% of Australia was used for agricultural activity: 3% for crops, 3% for pastures and grasses, with the remaining 53% of land holdings mainly used for grazing. Different agricultural activity affects the land in different ways, and the effects of land clearance (a necessity if crops are to be grown or pasture sown) are discussed in the headline indicator Land clearance.
Once land has been cleared of native vegetation, the impacts of agriculture depend on the crops grown and farming practices used. A detailed treatment of those impacts is beyond the scope of this publication, although the headline commentaries Land degradation and Inland waters discuss some of them. While 24 million hectares (ha) of Australian land were used for growing crops in 2000, far more of Australia was used for grazing sheep and cattle.
Until recently, interest in the links between changes in land use and the conservation of Australian biodiversity have focused on southern and eastern Australia where broad-scale clearing has been widespread.(SEE FOOTNOTE 1) There is now a growing appreciation of the effects of changes in land use on central, western and northern Australia.
The pastoral industry covers about half of the continent. Numbers of cattle have tripled since 1900, from 9.4 million cattle to 27.6 million. Numbers of sheep were 70% higher in 2000 than they were in 1900 (almost 120 million sheep in 2000 compared to a little over 72 million at the start of the last century). But sheep numbers at the end of the 1990s were considerably lower than periods in the 1960s, 1970s and late 80s. The national flock peaked in 1970 at almost 180 million animals.
Grazing by stock in arid and semi-arid regions exerts a pressure on the land and is one of the major threats to native vegetation (along with grazing by feral animals and change in fire frequency).(SEE FOOTNOTE 3)
Altered fire and hydrological regimes (see Biodiversity, and Inland waters) and invasive species (including exotic grasses introduced in an attempt to improve pasture) have had potentially significant effects on the biodiversity of arid and semi-arid Australia. Increases in the number of large herbivores have also had a direct impact. Domestic and feral livestock remove vegetation cover and break up the soil surface, exposing it to wind and water erosion, while an increase in pasture and numbers of watering points, and a reduction in dingoes, appear to have helped certain species of kangaroos to increase in numbers in some areas. Kangaroos also put pressure on vegetation cover.
Cattle and sheep numbers
There are many mines throughout Australia, though less than 1% of our total land area is used for mining or by mining leases.(SEE FOOTNOTE 4) Some sites are affected by land clearance or waste disposal, while the roads and infrastructure that provide access to remote mines have also had an impact on the environment.(SEE FOOTNOTE 4) Pollution from mine sites can affect the air, water and land, and some of the toxic compounds used to extract minerals at mines are a particular concern.
It is difficult to assess changes in the effects of mining on the Australian environment over recent years, but the mining industry has taken steps to reduce its impact on the environment. In 1996, for example, the Minerals Council of Australia instituted a self-regulating environmental code of practice to provide effective monitoring and reporting of mine site and mineral processing operations. Forty companies had signed up to the revised code by June 2001.
In 2001 there were an estimated 164 million ha of native forest in Australia. Our forests are an important carbon sink (i.e. they absorb the greenhouse gas CO2, as discussed in the Greenhouse gases commentary). They are used for many purposes, including recreation, biodiversity conservation, timber harvesting (the forestry industry and associated wood and paper manufacturing are important sources of income and work in Australia, particularly for some towns), water catchment protection and honey production. All of these uses have impacts, but the extraction of timber has attracted most attention.
The environmental impacts of timber harvesting are of greatest concern in native forests, where clearfelling and associated fire regimes frequently result in major changes to the species composition and structure of forests.(SEE FOOTNOTE 5) Forestry can damage soil structure, cause siltation of streams and rivers, and assist invasive plants and animals to spread.
One major impact of timber extraction is on animals that live in tree hollows. About one in seven of our vertebrate species (mammals, birds, frogs and reptiles) depend on tree hollows.(SEE FOOTNOTE 8) Suitable large hollows tend only to develop in trees older than 150 years, but sections of forests are typically logged every 55-120 years,(SEE FOOTNOTE 8) which means that large hollows will not develop in logged forests unless habitat trees are retained by forest management agencies.
The number of trees left standing to develop hollows has increased in recent years because of changes to the Codes of Forest Practice during the Regional Forest Agreement process (see box). In south-east NSW for example, only one hollow bearing tree was retained on every three hectares in 1991. By 1997 this had risen to 15 trees retained on every three hectares.(SEE FOOTNOTE 9)
In 2001 there were over 164 million ha of native forest in Australia. More than 12% of this forest was in nature conservation reserves. The majority of native forest in Australia was eucalypt forest (over 80%), with acacia forest accounting for another 10%.
Assessing change in forest areas during the 1990s is difficult. Although the National Forest Inventory released data for Australia's forest area in both 1997 and 2001, changes between the two years come from a range of factors, particularly from improvements in mapping, as well as actual change in forest area.
See also the commentaries Land clearance, Biodiversity, National income, National wealth, Work, Invasive species, and Greenhouse gases.
Native forest tenure - 2001
1 State of the Environment Advisory Council (SoE) 2002, Australia - State of the Environment Report 2001, SoE, CSIRO Publishing, Melbourne.
2 The Natural Heritage Trust 2001, The Journal of the Natural Heritage Trust, No. 10, Environment Australia and Agriculture, Fisheries and Forestry - Australia, Canberra.
3 National Land and Water Resources Audit (NLWRA) 2001, Rangelands - Tracking Changes, NLWRA, Canberra.
4 State of the Environment Advisory Council 1996, Australia - State of the Environment Report 1996, SoE, CSIRO Publishing, Melbourne.
5 Mackey, B., Leslie, R., Lindenmayer, H., Nix, H. and Incoll, R. 1998, The Role of Wilderness in Nature Conservation: A Report to the Australian and World Heritage Group, Environment Australia, Canberra.
6 Burns, K., Walker, D. and Hansard, A. 1999, Forest Plantations on Cleared Agricultural Land in Australia: A Regional Economic Assessment, Australian Bureau of Agricultural Research Economics (ABARE) Research Report 99.11, Canberra.
7 Bureau of Rural Sciences 2001. National Forest Inventory Database, BRS, Canberra.
8 Gibbons, P., Lindenmayer, D.B., Barry, S.C. and Tanton, M.T. 2000, "Hollow formation in eucalypts from temperate forests in south eastern Australia", in Pacific Conservation Biology, Vol. 6, pp. 218-228.
9 Recher, H.F. 1996, "Conservation and management of eucalypt forest vertebrates" in Conservation of Faunal Diversity in Forested Landscape, eds DeGraff, R. and Miller, I., pp. 339-388, Chapman and Hall, London.