Some Effects of Forest Change on Water Values

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Abstract
Forest change can have a marked effect on water quality, water yield and storm-flow peaks with the magnitude of the effect depending on the specific site conditions. Water quality degrade can result from the removal of forest cover, soil disturbance, and the application of fertiliser, insecticides and herbicides. Steep slopes and poorly strucured shallow soils, either alone or in combination can increase the risk and extent of any degrade. Alterations in forest cover can result in marked changes in water yield and peak flow. Some forest changes, for example wildfire, can occur on a scale sufficient to assume immediate regional significance. Small scale forest changes can, if extended, build up over time until they are of regional significance, for example the destruction of jarrah forest by the cinnamon fungus or the conversion of dry sclerophyll forest to pine. Small community water supply systems with limited storage and treatment facilities are particularly sensitive to changes in the yield and quality of water. There is no doubt that good management practices can reduce the impact of forest operations on soil and water values. There is also evidence that the development of forest management strategies to control streamflow volumes may be possible for specific forest types such as jarrah, karri, mountain ash and radiata pine. In many regions of Australia intensive forestry practices will replace extensive forestry practices and conifer forests will become increasingly important. These regions are also areas where it is likely that increasing demands will be made on the water resources. The forest manager should be aware of the potential effect of forest operations and change on the water values.