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    Science explaining logging water loss

    What is Clearfell logging Ash forests?

    Wood-fibre is taken from biodiverse native forests in the Melbourne catchments using a highly destructive practice called Clearfell Logging.

    Clearfell Logging involves the removal of almost all vegetation from a given area, leaving the site bare and the soil highly disturbed. The process is similar to clearing the forest for agricultural purposes. After logging the area is burnt using napalm.

    Clearfell logging dramatically reduces water available from catchments.

    Ash Regrowth after clearfell logging

    Close inspection of ash regrowth after clearfell logging reveals a young, dense, even-aged plantation of young trees has established. It is these young ash trees that grow after logging that cause, water runoff decreases due to the trees transpiring water from their leaves. Click here to see further information on this.

    Regrowth after clerarfell logging

    Denser regrowth ash in the Thomson after clearfell logging

    When Mountain Ash forest is logged in Melbourne’s water catchments, the regrowth is very dense and therefore has a large number of leaves (see photo below). The greater the leaf area, the greater the transpiration or water loss. The dense regrowth in Melbourne’s catchments is literally sucking water into the air, so it isn’t available for Melbourne.

    Dense regrowth growing after clearfell logging

    Young ash trees transpire more water

    When trees and other plants grow they suck water up from the ground and transpire water from their leaves – a bit like people sweating. The image below shows the water movement into, out of and within forests.

    Water movement in forests

    Source: Predicting Water Yields From Mountain Ash Forest Catchments Zithromax online Industry Report of the Co-operative Research Centre for Catchment Hydrology, April 1998. Fig 1, Pg 1.

    Water lost through logging is significant

    The Kuczera Curve (below) shows how much water is lost when Mountain Ash Forest (like that in Melbourne’s catchments) is logged. It shows that

    • 30-40 years after forest is logged, average water yields will be reduced by 50%; and
    • It takes 150-200 years for the water yield to return to pre-logging levels.

    Logging in Melbourne’s water catchments is concentrated in the high rainfall Mountain Ash Forests, so the impact of the logging across the catchments is dramatic.

    Kuczera Curve showing loss of water due to logging in Melbourne's catchments.

    Clearfell logging is concentrated in high rainfall areas of Melbourne’s catchments.

    Clearfell logging in State Forest within the Thomson catchment shows that clearfell logging is clearly concentrated along the high rainfall slopes of Mt Baw Baw. (Click on image below to enlarge.)

    Logging in Thomson catchment target high rainfall areas.

    Logging debate has been going for two decades.

    Independent research by Read Sturgess and Associates in 1992 indicated that if logging in the Thomson catchment was stopped , mean annual flow would increase by more than 20% in 60 years (see graph below).

    Water yield from Thomson catchment

    Over the past two decades many studies have shown the dramatic impact that logging has on water output from Melbourne catchments.

    The results of the latest studies are here .

    Research and inquiries concluded catchment logging reduces Melbourne water supply.

    For the past fifteen years there has been considerable public concern regarding the impacts logging has on the quantity and quality of water in Melbourne’s catchments. Past community concern has led to the State government conducting numerous inquiries and research projects that have concluded logging should be stopped.

    • 1992 Read Sturgess and Associates Evaluation of the Economic Values of Wood and Water for the Thompson Catchment.
      Conclusions: If logging suspended in the Thomson, the community nett benefit would be $157 million p.a.
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    • 1994 Read Sturgess and Associates Phase Two of the Study into the Economic Evaluation of Wood and Water for the Thompson Catchment (unpublished).
      Conclusions: Similar to 1992 Read Sturgess report.
    • 2000 Creedy and Wurzbacher The economic value of a forested catchment with timber, water and carbon sequestration essay writing uk benefits Ecological Economics 38 (2001) 71-83.
      Conclusions: net present value of water is three times greater than timber.
    • 2002 Infrastructure Planning Council Final Report.
      Recommended phase-out of logging in Melbourne catchments. Naltrexone no prescription
    • 2002 Water Resources Strategy Committee for the Melbourne area
    • Recommended that a transition strategy for the cessation of logging be completed by 2004

    Further information

    The reports listed above can be used for further information, in addition to the following resources:
    • Predicting Water Yields From Mountain Ash Forest Catchments’ Industry Report of the Co-operative Research Centre for Catchment Hydrology, April 1998.