Collapse of mountain ash ecology threatens Melbourne's water supply

Melbourne's Water Supply Is At Risk, Thanks To Over-Logging

Gizmodo,

1 May, 2018

Victoria's Mountain Ash forest generates nearly all of Melbourne's water. It is also facing "imminent collapse" due to a radical change in the ecosystem.

The Australian National University are behind the discovery, with the release of a 35 year study that provides the first empirical evidence of the disastrous effects of over-logging.

Lead researcher Professor David Lindenmayer, from the ANU Fenner School of Environment and Society, says wildfires combined with over-logging have tipped the Mountain Ash forest "very close to collapse".

"Collapse" of a forest is indicated by marked changes in the condition of an ecosystem - particularly the rapid decline in populations of key plants and animals.

"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.

This could be avoided by having better forest policy and greater political will to save the forest's large old trees, Professor Lindenmayer said.

A primary cause of the imminent collapse was the loss of half of the population of large old cavity trees, which many animals depend on, over the past two decades. Replacing the lost cavity trees would take 50 years.

"The numbers of Leadbeater's Possum, the Greater Glider and other arboreal marsupial species dependent on these big old trees have dropped by 50 to 65 per cent," Professor Lindenmayer said. "Since 2004, there have been significant declines in almost all species of tree-cavity reliant bird species including the Laughing Kookaburra and Crimson Rosella."

But what exactly will happen if the forest collapses?

The Mountain Ash trees, which can grow up to 100 metres tall, would likely be replaced by Acacia shrubs as the dominant plant species. This would mean a dramatic change in the ecosystem.

The Mountain Ash forest 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.

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

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