Land clearing involves the removal of native vegetation and habitats, including the bulldozing of native bushlands, forests, savannah, woodlands and native grasslands and the draining of natural wetlands for replacement with agriculture, urban and other land uses. As much as 70% of Australia's native vegetation has been cleared or modified in the past 200 years, most of which has occurred in the last 50 years.
Prior to European settlement native vegetation covered most of Australia but now only 87% of the country is vegetated by native species. In total 13% of Australia's native vegetation has been lost due to land clearing, with the majority of this being native forests and woodlands.
The primary motivator for land clearing in Australia is agricultural profit. The clearing of land allows for increased agricultural production and increase in land values. Land clearing was seen as progressive, and there was the general view that land was wasted unless it was developed.
Historically, land clearing has been supported by the Commonwealth and State Governments as an essential part of improved productivity essential for national economic prosperity.a range of institutional incentives for agriculture increased the economic gain from land clearing, with offerings of cheap land along with venture capital in the form of loans or tax concessions. Other incentives included the War Service Land Settlement Scheme, low interest bank loans and financial support programs such as drought relief assistance.
The majority of cleared land in Australia has been developed for cattle, cotton and wheat production. In New South Wales, much of the remaining forest and woodland has been totally cleared, which is due largely to the high productivity of the land for agricultural purposes. Urban development is also the cause of some land clearing, though not a major driver. In The Australian Capital Territory for example, much urban development has occurred on previously cleared agricultural land.
Since the 1980's, the rate of land clearing has declined due to changing attitudes and greater awareness of the damaging effects of clearing. Clearing is now controlled by legislation in Western Australia, South Australia, Victoria, New South Wales, and to a lesser degree in Queensland. Land clearing controls differ substantially between jurisdictions, and despite growing awareness of the effect of land degradation, controls on clearing have been generally opposed by farmers.
Land clearing destroys plants and local ecosystems and removes the food and habitat on which other native species rely. Clearing allows weeds and invasive animals to spread, affects greenhouse gas emissions and can lead to soil degradation, such as erosion and salinity, which in turn can affect water quality.
The following table shows the Native Vegetation Inventory Assessment (NVIS) of native vegetation by type prior to European settlement and as at 2001-2004.
|Vegetation Type||Pre Settlement Total||2005 Total||Percentage Lost|
|Forest and Woodland||4,101,868||3,184,260||22%|
|Total Native Vegetation||7,578,204||6,562,541||13%|
As land cover is crucial to land condition, land clearing exerts significant pressure on land condition. Removal of vegetation also leaves soil bare and vulnerable to erosion. Soil stability is essential to avoid land degradation.
Soil erosion is a very significant pressure on land condition because it undermines existing vegetation and habitats and inhibits vegetation and other biota that inhabit the vegetation from re-establishing. Terrestrial vegetation is a source of nutrient replenishment for soils. If vegetation is removed, there is less biological matter available to break down and replenish the nutrients in the soil. Exposing soil to erosion leads to further nutrient depletion.
Another consequence of land clearing is dryland salinity. Dryland salinity is the movement of salt to the land surface via groundwater. In Australia there are vast amounts of salt stored beneath the land surface. Much of Australian native vegetation has adapted to low rainfall conditions, and use deep root systems to take advantage of any available water beneath the surface. In this way, plant roots help to store salt in the earth, by keeping ground water levels low enough so that salt is not pushed to the surface. However, with the removal of plants due to land clearing, the amount of water leaking into the groundwater beneath the root system means that the water table rises to the surface along with salt. Salinity reduces plant productivity and affects the health of rivers and streams.
The extinction of 20 different mammal, 12 bird and 97 plant species have been partially attributed to land clearing. While land condition is one indicator of the pressure of vegetation removal, the health and resilience of the vegetation that remains is also largely dependent on the size of the fragments and their distance from each other. This is also true for species living within these habitat fragments. The smaller and more isolated the remnants, the greater the threat from external pressures as their boundaries (or edges) are more exposed to disturbances Pressure also increases with the distance to be traversed between fragments.
Land clearing is a major source of Australia’s greenhouse gas emissions, and contributes to approximately 12 percent of Australia’s total emissions in 1998. It has also been found that past clearing of native vegetation contributed to higher temperatures, decreased rainfall and more intense droughts. The removal of vegetation damages the microclimate by removing shade and reducing humidity. It also contributes to global climate change by diminishing the capacity of the world’s vegetation to absorb carbon dioxide.