Catchment water runoff process
Catchment water runoff process.
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Water catchments

Fire affects the type, structure and condition of vegetation and therefore has a significant role to play in water productivity from catchments.

Catchments with vegetation cover that protects the soil from erosion produce clear, clean water that requires very little treatment before it gets to the consumer’s tap. However, a heavy vegetation layer means much of the rainfall is intercepted and used by the vegetation, significantly decreasing the amount available as runoff into streams, rivers, dams or infiltration into ground water aquifers.

Fire can be used to manage catchment vegetation to ensure there is enough cover to maintain water quality for environmental reasons while optimising the amount of potable water. Low intensity prescribed burns reduce the amount of vegetation and ground cover to increase runoff without affecting water quality. Intense bushfires expose the soil surface and lead to erosion. This can impact catchments by depositing silt and ash that block drainage channels. Bushfires also impact water storages, by causing turbidity, dissolving of nutrients, algal blooms, fish kills and increased water treatment costs.

Fire fact

Prescribed burns applied to ground water catchments can increase water production for up to five years after the burn.

Fire affects to soil structure
Fire affects to soil structure.
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Much of Australia’s soil is ancient and therefore among the most nutrient poor in the world. Nutrients available for plant growth usually exist in the top ten centimetres of the soil and much of it is locked up in the biomass of the plants and animals that need it. The rate at which new nutrients are made available to the soil from decomposing bedrock is extremely slow, which means the cycling of existing nutrients is pivotal to sustaining Australian ecosystems.

Contributing elements to soil formation
Contributing elements to soil formation.
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Regular fire in the landscape is a primary mechanism to cycle nutrients through the soil, particularly in the drier parts of the landscape, where decomposition of biological material is usually very slow. Without fire, a great deal of available nutrients would remain locked away in forms not available for use by growing plants. The number and diversity of animals that depend on those plants would also be affected.

Fire in the north of Australia

The plants and animals of the Kimberley and other northern parts of Australia are resilient to fire, so even fires late in the dry season (July-November) are not nearly as destructive as they may appear. However, repeated intense fires late in the dry season can significantly reduce tree cover, and can be harmful to a range of animals.

Land managers use prescribed burning during the early dry season (May-June), when the ground vegetation is not fully dried and fire tends to be relatively low in intensity, patchy and limited in extent. These fires reduce fuel, which limits the spread of higher intensity bushfires late in the dry season.

Parks and Wildlife scientist Ian Radford has conducted valuable research about fire in the north of Australia (see ‘Fire in the Kimberley’ in LANDSCOPE magazine for more information).

Fire fact

The vegetation growth that is produced each wet season quickly dries out, which provides the following dry season with a large amount of fuel for fires.

  • Prescribed burning in the Kimberley.
  • Wet season prescribed burning at Silent Grove, King Leopold Range Conservation Park.
  • Serious soil erosion and sediment movement in streams following high intensity summer bushfires in the jarrah forests.