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Impending forest collapse threatens Melbourne’s water supply

Victoria’s Mountain Ash forest is on the verge of collapse, and with it the security of water supply for Melbourne’s 4.5 million residents, according to a landmark study from the Australian National University.

 The study, led by Professor David Lindenmayer, is based on 35 years of research, and is the first empirical evidence produced indicating the forest is facing imminent collapsse.

 “Wildfires and over-logging have tipped the Mountain Ash forest very close to collapse – populations of animals living there have halved, and in some cases have declined by more than 65 per cent during the past 20 years,” said Professor Lindenmayer, who is from the ANU Fenner School of Environment and Society.

 He said a primary cause was the loss of half of the population of large old cavity trees, which many animals depend on, over the past two decades.

 If collapse were to occur, the Mountain Ash trees, which can grow up to 100 metres tall, would likely be replaced by Acacia shrubs as the dominant plant species, resulting in a dramatic change in the ecosystem.

 “If we don’t act quickly to turn this dire situation around, we will have a crisis on our hands,” Professor Lindenmayer said.

“Not only does the Mountain Ash forest in Victoria generate nearly all of the water for the 4.5 million people living in Melbourne, it also stores large amounts of biomass carbon and supports timber, pulpwood and tourism industries.”

He said the forests were currently in “hidden collapse” as while they appeared intact superficially, “the prolonged period of decline coupled with long lag times for recovery means that collapse is inevitable”.

Professor Lindenmayer said replacing the lost cavity trees would take 50 years, and the trees that remained needed to be protected.    

“We urgently need major changes to forest policy to rectify this situation, especially greater protection for large old trees,” he said. 

“Our study of the collapse of the Mountain Ash forests in Victoria is unusual among these examples as it describes a forest during, rather than after, the process of collapse.”

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