State of the Environment Report 2007
Western Australia has a total land area of 253 million hectares, equivalent to one-third of Australia. The Western Plateau is the dominant landmass, consisting of very old rocks, some over 3000 million years old. Several areas have been given individual 'plateau' names such as Kimberley, Hamersley, Arnhem Land and Yilgarn. In the Perth area, younger rocks along the Swan Coastal Plain are separated from older parts by the Darling Fault escarpment. The Nullarbor Plain is an uplifted limestone sea floor, estimated to be 25 million years old.
The land resource is fundamental for sustaining life and ecological processes. It is essential for supporting native ecosystems and maintaining biodiversity; providing a foundation for humans to live; supporting the production of food, fibre, timber and minerals; preserving historical and landscape information; and supporting spiritual, recreational, scientific, cultural and educational values.
Landscapes include landform, soils, human settlements and all natural resources and ecosystems on the land, including inland waters and biodiversity. However, landform and soils are the focus of this theme; the other aspects of landscape have been addressed elsewhere in this report. The land resource has been highly modified since European settlement. Native vegetation, which provides a protective cover for the land, has been removed or degraded in many areas to allow for urbanisation, agriculture, mining, pastoralism and infrastructure development (including buildings, pipelines, roads and railways). The amount and rate of removal or degradation of native vegetation is a consequence of population growth, the consumption of natural resources to support it and economic productivity (see 'Fundamental pressures'). Altering land from its natural state inevitably results in changes to soil health and landscape functionality. If persistent, these changes can lead to environmental problems and rapid deterioration of both aquatic and terrestrial ecosystems.
The State Salinity Strategy lists specific goals for managing the impact of land salinisation in the South West agricultural zone (Government of Western Australia, 2000). Objectives relevant to the land resource include to:
Land Monitor satellite images between 1996 and 2004 provide a measure of change in vegetation cover, with 64% of monitored bioregions showing a net decline and 36% showing a net increase. There are thirteen bioregions in the South West, which includes the land between Geraldton and Esperance. A decline in South West vegetation cover is likely to have contributed to several land issues including salinisation, erosion and loss of soil health. There was no information available for two of 13 bioregions.
Declines in rangeland vegetation contribute to soil erosion and loss of soil health. Changes to perennial shrubland density and grassland frequency are assessed at sites in the Western Australian Rangelands Monitoring System (WARMS). Site comparisons were made between recent and historical assessments - roughly three years apart in the Kimberley and five years apart in other rangeland areas. Only 22% of monitored bioregions showed a net decline in rangeland vegetation (that is, more sites showed a decline compared to those that remained stable or improved). Seventy eight per cent of monitored bioregions showed either no change or a net increase in rangeland vegetation. There was insufficient or no information for 14 of 41 bioregions in the State's rangelands, located mostly in the interior desert region.
Landforms are the terrain and underlying rocks and soils that help shape the land. In WA they include major features such as basins, plains, plateaus and ranges, and minor features such as hills, valleys, slopes and dunes. Mining activities, road construction and development of human settlements have the largest impact on natural landforms. Mining involves the extraction of minerals and ores from hills and ranges (e.g. pits or quarries), often resulting in significant landform modification. New landforms can be created (e.g. artificial hills) as a result of dumping of waste rock left over from mining. Landforms are also modified to make the land more suitable for human settlements, such as providing for transport, infrastructure, and the construction of houses. At this time, it is not possible to broadly assess landform condition in WA.
Soils consist of small rock and mineral particles (which may include mixtures of clay, silt, sand and gravel), organic material, air, moisture and living organisms. Humans often modify soil properties to enhance plant growth, build infrastructure, increase water infiltration, and resist erosion by wind and water. When soils are used beyond their natural capacity, soil rehabilitation and treatments are often required. Generally, information about soil condition is only collected where it is considered to be of value for determining agricultural or pastoral productivity. At this time, it is not possible to broadly assess soil condition in WA.
Agricultural productivity can provide a general indication of soil condition. Soils in good condition are generally more productive and profitable than those with nutrient deficiency, poor structure, low organic content, or affected by salinisation, acidification, contamination or erosion. Profit-at-full equity for farmland represents the economic return on the land from agriculture and pastoralism (Commonwealth of Australia, 2001b; Figure L0.1). These data must be interpreted with some caution given their age and the limited number of farms actually surveyed. However they provide a general indication of land productivity across the State. Land in the South West is generally more profitable than in the rangelands where returns are typically lower. However, negative returns are also evident in some parts of the South West, which may indicate marginal productive farmland or land degradation problems (such as salinisation, acidification, erosion and loss of soil health). While there are many options to make soils more productive, the challenge is to ensure these methods are implemented across a wide scale.
![Figure L0.1: Profit-at-full-equity for agriculture, a five-year average, 1992–97. [Data source: CSIRO [ver.1997]; Analysis: CSIRO; Presentation: EPA.]](/site/files/images/Figure-L0.1_Large.jpg)
Fifty actions were identified for the 'Land' theme in response to the 1998 State of the Environment Report (Government of Western Australia, 1998). Of these 28% remain incomplete, 60% have been completed but not evaluated, and only 12% have been completed and evaluated. With the exception of land salinisation, monitoring of other land issues is sparse and relies heavily on modelling. In addition, the effects of on-ground actions are difficult to detect and it may take many years of monitoring before environmental outcomes become apparent. Consequently, even though a large proportion of these programs are complete, it has been very difficult to evaluate actual environmental outcomes, and increased monitoring and evaluation efforts are urgently needed. Initiatives of the National Action Plan for Salinity and Water Quality and the Natural Heritage Trust programs may improve monitoring of land issues, such as land salinity, soil erosion and soil acidification.
3.1 Develop and implement a State Soil Protection Policy to ensure that all soil resources are managed in a sustainable manner and protected for the long term.
See also 'Loss of degradation of native vegetation':
