The Institute of Foresters of Australia (IFA) has sought Government action over the current critical situation of the streams and forests in WA, and says that adaptive management is really the only sensible option available.
The institute spelled out its concerns in a letter to the WA Premier, C.J.Barnett.
Forested catchment management
The Institute of Foresters of Australia (IFA) is the professional association for forest scientists and managers of forested land. The IFA sees no issue of greater social, environmental and economic importance than the proper management of forested water catchments. A reduction in surface soil moisture in the higher rainfall water catchment forests is impacting adversely on the health of forest and stream ecosystems while water yields are declining.
The IFA strongly supports the Water Corporation’s Wungong Project and considers that it is appropriate for forest management in the Perth water supply catchments to prioritize water quality and quantity to provide low-cost water resources. Alternative forest management practices are required in the higher rainfall areas of State forest on water supply catchments.
Our concerns relate primarily to the declining health of the catchment streams, forests and the stream biodiversity. These concerns were prompted by:
a seventy five percent reduction in stream flows into dams;
a fall of many metres in regional water tables;
summer drying of streams that were once considered as perennial with
consequent changes to the stream biota and;
the deaths of large, old trees on shallower soils.
The main causes of these changes are:
decreasing total rainfall in catchment areas;
changes to the intensity and the timing of rainfall, including an absence over
the past 30 years of well above average rainfall events;
falling water tables in stream lines of about 2 m since 1995, leading to
disconnection between the surface and the shallow groundwater table;
substantial decrease in runoff since then, for any given rainfall;
fire regimes of more intense fires with less fuel reduction burning;
forest that is overstocked and out of balance with the current climate which
evaporates or transpires 85-95 percent of rainfall so that it is now “mining”
The prognosis is that all these factors will be even worse in the future.
Necessary alternative forest management practices include designating “Water” as
the priority management objective on about 100,000 hectares of State forest in the
higher rainfall zone.
Overstocked forests should be thinned to reduce canopy cover to about one
third of its present density to a maximum basal area of 10-12 square
metres/hectare and with subsequent control of coppice regrowth. Recurrent
thinning and coppice control will be required.
Regular prescribed burning with a maximum seven-year cycle.
The abolition of non-essential Fauna Habitat Zones (where thinning is not
permitted) within the priority water supply catchments
Retention of stream zones to a maximum width of 50 m either side of the
Concentration of thinning activity in those parts of the landscape where it will
be most effective.
If these practices are employed over the 100,000ha of forested water catchment,
it is conservatively estimated that an additional 30gL per year of highest quality
fresh water for Perth could be produced at a fraction of the economic,
environmental and social cost of developing other drinking water sources.
The Institute recommends that you instruct your various Ministers and
Departments to work quickly, cooperatively, in full partnership and efficiently if
this goal is to be achieved. This includes the Ministries that cover Conservation
and Environment, Water, Water Corporation and Forest Products. Time is of the
The Institute recommends that you require workable, field based, management
solutions to be presented to you within three months, for implementation within
six months. The Wungong and 31 Mile Brook research study areas should receive
There will always be a need for further research and monitoring. However, it is
recommended that the Government act now on what is known (which is a lot)
rather than what may (or may not) be learnt in the future. In the current critical
situation for the streams and forests, adaptive management is really the only
sensible option available.
The Institute would be pleased to be part of the “solution” and offers our full
support in progressing this matter professionally and scientifically
Yours sincerely, David Wettenhall, RPF, MIFA, MACFA
Chair, IFA WA Division.