The Age, 12 Sep 2011
BEFORE European settlement up to 80 per cent of the wet eucalyptus forest of Victoria's central highlands was old-growth mountain ash, with trees taller than 90 metres towering above the landscape.
According to research published in US journal the Proceedings of the National Academy of Sciences, the old-growth is nearly gone and on the verge of being unrecoverable.
The paper says decades of logging and frequent bushfire have reduced the area of old-growth to about 2000 hectares - 1.2 per cent of the forest area north-east of Healesville.
Lead researcher David Lindenmayer, from Australian National University's Fenner School of Environment and Society, said if the current combination of clearfelling and fire continued the mountain ash could be lost and replaced by wattle, or ''acacia scrub''.
''This forest is one of the saddest things I've ever seen in 30 years of ecological science. What we are seeing is a truly iconic forest evaporating before our eyes and it will never be the same again,'' Professor
''If it collapses into acacia scrub, it is impossible to get out again. It really is a catastrophe in the true sense of the word.''
The paper says Victoria's central highlands forest is an example of a ''landscape trap'' - a new label for an ecosystem that is fundamentally changed through human action and natural disturbance.
More than 150 years ago the central highlands were dominated by forests aged 200 to 450 years, and regulated by infrequent late summer wildfires that released seedlings from burnt trees to produce new stands.
According to the paper, in the past century the natural cycle has been disturbed by more frequent bushfires - there have been at least five, including Black Saturday in 2009 - and clearfell logging for pulp and timber.
It says the frequency and severity of fires has been exacerbated by the reduction in rainfall and overall forest age in recent decades - young mountain ash saplings are densely packed and more likely to burn.
When the time between regenerating events is less than 20-30 years, mountain ash is at risk by being replaced by other species.
Professor Lindenmayer said the loss of mountain ash had a huge impact on biodiversity, water supply for Melbourne's catchments and carbon dioxide emissions.
A 2009 paper found the central highlands' forest was the most carbon-dense in the world.
About 40 local vertebrate species rely on old-growth tree hollows for habitat.
Trees older than 100 years are no longer logged, but Professor Lindenmayer said fixing the landscape trap would require ending clearfell logging and trying to limit future fires through prescribed burning in some areas to reduce the risk to surviving old-growth.
''What is really needed now is restorative forestry, not industrial forestry, which is what we've got now,'' he said.
State government-owned timber agency VicForests says it operates sustainably.
Last week it released a consultant's report that found claims that plantation timber could completely replace native forest wood in Victoria were unrealistic.
The paper comes as conservation group My Environment is applying for a court injunction to stop logging in three forest coupes near Toolangi on the grounds they could be home to the endangered Leadbeater's possum.
The case is scheduled to be heard in the Supreme Court next week.