Australasian Science: Australia's authority on science since 1938

Top 10 Ecosystems Under Threat

By Stephen Luntz

Twenty-six ecologists have come together to rate the environmental vulnerability of Australia’s ecosystems, producing an endangered Top 10. Heading up the list are our mountain ecosystems, with global warming, fire and development posing the primary threats.

While it is hardly news that global warming may leave cool alpine species with nowhere to go, the second most endangered landscape is our tropical savannas. They may be mostly far from human activities, but invasive grasses are wrecking havoc on the savannas and many native mammals are unable to adapt to the new arrivals. Moreover, the ecologists agreed that a change in regime from cool, early season fires to larger conflagrations later in the year is pushing much of the top end towards ecological collapse.

It took 18 months for the results of the conference to be published in Biological Conservation, during which time the Murray-Darling Basin, ranked sixth at the time, gained a lifeline in the form of two wet years. “The longer you have dry years the more that eats into your resilience,” says Dr Ben Gawne of the Murray-Darling Freshwater Research Centre. “When boom times come they offer a chance to recover, but a lot of trees put on a burst of leaves in the first flood. If that is not followed up it can be the last gasp. With a sequence of floods the prospects are better.”

However, while healthy river red gums can survive 10–15 years before the next big flood, for many bird species the period before they need to breed is shorter. Moreover, Gawne says that the problem is different for the Coorong at the mouth of the Murray River in South Australia. “The floodplains have suffered from the lack of intermittent floods, but the Coorong is suffering from the loss of baseline flows, so after a couple of years if we don’t implement the Murray-Darling Basin Plan the dangers will rise dramatically.”

In each case the scientists agreed that the ecosystems are approaching a tipping point, which Gawne describes as “a threshold beyond which an ecosystem may change rapidly and irreversibly into alien landscape, often dominated by introduced or unfamiliar species”.

The ranking was based on how far the scientists, each specialising in different areas, considered each landscape to be from such a tipping point. “It means that unless we act with speed and decision, there are Australian landscapes today our grandchildren will never get to see,” Gawne says.