Extinction threat for Wet Tropic possums

Ringtail possum populations in Queensland's Wet Tropics could be wiped out in less than three decades as climate change, including extreme heatwaves, causes population decline.

Populations at lower elevations have been declining to basically "local extinction" as possums that evolved in cool rainforests are forced into higher altitudes, James Cook University Professor Stephen Williams says.

"It's been creeping up the mountain, we've seen them disappear at 600 metres, then almost disappear at 700 metres and at 800 metres they're less than 50 per cent of the abundance they used to be," he said.

Most of the mountains in the region are just over 100 metres at their peak.

"They're basically just getting pushed up with not very many places to go ... nowhere to go really," Prof Williams says.

His paper with PhD candidate Alejandro de la Fuente analysed a long-term ringtail population survey conducted between 1992 and 2021 in the Wet Tropics.

It found the negative impacts of climate change, including extreme heatwaves, has resulted in a rapid decline in ringtail possum populations over the past three decades.

"Somewhere between 2010 and 2014 ... things just started to get too bad, and the combination of increasing temperatures and increasing frequency and intensity of heatwaves have just caused this exponential decline," Prof Williams said.

"Almost any of the future models now, under any scenario of (emissions) reductions, predict there's going to be very serious impacts."

In heatwave years, analysis suggests there is likely both an increase in the death rate and a decline in reproduction rates.

"We haven't actually observed possums falling out of trees ... but what we do know is that whenever we have a year or a couple of years in a row that have heatwaves, the numbers really crash," Prof Williams said.

Four species of ringtail possums live in the Wet Tropics - the Lemuroid Ringtail, Green Ringtail, Herbert River Ringtail and Daintree River Ringtail.

The findings have led him to nominate the Lemuroid Ringtail possum as endangered through the Environment Protection and Biodiversity Conservation Act.

The impact of climate change isn't confined to possums, and most of the unique birds that live in the rainforest have declined by between 30 to 50 per cent of their total population, and as well as pushed up to higher elevations.

Analysis suggests that even a moderate reduction in carbon emissions would help reduce extinction rates across all species in the Wet Tropics from over 50 per cent of the species down to as low as five per cent.

Long-term monitoring and "lots and lots" of fieldwork is key to understanding ecosystem health, but funding is not secure.

Funding for the region "really got cut" as political pressure pushed more toward the plight of the Great Barrier Reef, Prof Williams said.

"We've got these two amazing world heritage areas, the Great Barrier Reef and the Wet Tropics, side by side," he said.

"They're both big tourists attractions, both worth billions and billions of dollars in ecotourism.

"The rainforest has been a bit of a poor cousin compared to the reef."

Prof Williams said it was also critical to explore adaptation options for species in the World Heritage area.

"What this paper shows us is there's a big difference in the impacts of heatwaves versus long-term change," he said.

"Some species are most impacted by heatwaves while others are declining in association with gradual climatic change."