CircularPool WATC 000640-786
Circular Pool, Walpole
Photo © Tourism WA

Conserving soil and water is vital to:

Water

Water is an essential commodity for people, communities and various industries, and the quality of water determines how it is used.

Western Australia's south-west forests provide catchment areas for drinking water for most of the State's population, and water sources for recreation and industry.

  • Surface and groundwater supply, demand for its use and water quality are all considered in Forest Management Planning.
  • Records show rainfall has been declining in the south-west since the 1970s, which has affected streamflow and groundwater levels. For example, annual streamflow between 2004 and 2009 was 12 to 50 per cent less than the average between 1975 and 2003.
  • At the same time, population growth, mining, agriculture and horticulture in Western Australia are increasing the demand for water. This growth will also mean increased demand for recreation in public drinking water catchments.
  • A 2009 study by the CSIRO found the available surface water supply by 2030 was expected to drop around a quarter from the period 1975 to 2007, and groundwater supply was also expected to drop by around three per cent, in south-west Western Australia, including the metropolitan area.

With this in mind, the current Forest Management Plan has proposed changes to silvicultural practices, including thinning of vegetation to increase the water available to key areas that depend on surface water, such as important wetlands.

  • The maximum area that could be thinned is about 65,500 hectares.
  • Modelling for this strategy indicates that an extra 22 gigalitres of water a year could be produced on average for the first decade, and an extra 45 gigalitres a year after that with ongoing forest management.
  • Catchment management plans will be required where any proposal seeks to reduce stand density below the relevant silviculture guideline, or where a proposal would change a large proportion of the forest in the catchment to young trees, which may have greater water use than older stages of development.

Historically, the main risk to water quality in forested catchments was rising groundwater, which dissolved salt stored in the soil and brought it to the surface (salinity). However, groundwater levels are falling in the Department of Parks and Wildlife's Swan and South West regions and parts of the Warren Region because of reduced rainfall.

Timber harvesting will continue to be excluded from informal reserves along streams and rivers to protect water quality. These informal reserves also provide a network of undisturbed corridors through the forest for wildlife.

Soil

Soils, and the organic matter they contain, provide the physical, chemical and biological foundation necessary to support plant and animal life, and sustain ecological processes.

  • Soils affect how native plants grow, and consequently the habitats necessary for native animals.
  • Soils store and regulate the supply of nutrients and water essential for plant growth and development
  • Soils contain micro-organisms which regulate the supply of nutrients essential for the maintenance of healthy ecosystems
  • Uncultivated soils make positive contributions to global carbon cycles.

Soil disturbance, erosion, compaction and salinity can negatively affect soil carbon and fertility, and ecosystem and hydrological processes.

Disturbance to vegetation from mining, prescribed burning, road building, timber harvesting, pest animals and grazing can cause soil erosion, and may result in lower soil fertility and build up of sediments in rivers. Even small losses of soil are important and should be minimised.

Soil bulk density is a measure of the soil's physical properties that is important for fertility and hydrological processes. Soil-bound organic matter and above-ground organic debris are important to soil fertility because they contribute to the physical, chemical and biological properties of soil.

The protection of soil during timber harvesting and other activities in our State's south-west native forests was an area of major consideration during the development of the Forest Management Plan 2004-2013.

Further information

A series of subsidiary management guidelines were developed by the department to support the plan, including:

  • Soil and Water Conservation Guidelines (2009)
    • Manual of Procedures for the Management of Soils Associated With Timber Harvesting in Native Forests (2010)
    • Manual for the Management of Soils (2010)
    • Manual for the Management of Surface Water (2009)

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