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The white possum has been dubbed the polar bear of the rainforest (Image: Wet Tropics Images/Mike Trenerry)

We enter Australia’s lost world of species marooned by evolution to meet one of its rarest, a creature uniquely vulnerable to climate change

IT TAKES less than three hours to travel from the busy tarmac of Cairns Airport, back 100 million years to . By the time the sprawling malls and suburban estates have given way to blue sky and sugar cane, we have already rewound several decades. Veering inland, we swim against the tourist tide streaming towards the Great Barrier Reef. As jungle encloses us, the notion that we have crossed into a more primitive dimension is encouraged by road signs cautioning drivers to watch out for southern cassowaries – stroppy, flightless birds sometimes likened to prehistoric turkeys.

A boom gate restricts access to the sanctum of Mount Lewis National Park, to stop it being loved to death by naturalists and birdwatchers. The barrier rises and the rugged track lurches through some of the most ancient landscape on the planet, a dense tangle of living fossils. There are conifer species here that evolved more than 200 million years ago, but the dominant flowering plants are a mere 60 to 120 million years old.

At 1200 metres above sea level, the track gives up. This is the cloud forest, where mountain peaks float like cool islands in mist from the Coral Sea. Marooned up here are creatures of a lost world, with such fine-tuned adaptations that they can never leave.

Fifty million years ago, rainforests covered two-thirds of Australia, but as the continent drifted into warmer latitudes they gradually dried and shrank. They are now confined to a 450-kilometre ribbon along the far north-east coast. Although these rainforests cover just 0.1 per cent of the Australian landscape, , including two-thirds of the butterfly species, half of the birds and a third of the mammals. There are 100 vertebrate species in this rainforest that are found nowhere else. We are here in search of one of the most elusive, the white lemuroid ringtail possum.

Australia’s Wet Tropics is a World Heritage Site. Out of more than 173,000 places protected globally, named it as the sixth most valuable overall and the . It is also one of the most threatened ecosystems, . The predicted problems include higher temperatures, longer dry seasons, erratic rainfall and increased evaporation.

I am here with Stephen Williams and his team from James Cook University in Queensland. They have been closely monitoring conditions and species in the Wet Tropics for more than a decade, indeed up to 20 years in some locations. According to their findings, the future is already here.

In 2003, when most climate concern was focused on icy high latitudes, . Here temperatures vary little between summer and winter, or even day and night. Temperature is tied to elevation: for every 1000 metres you ascend, it drops by an average of 6 °C. Species occupy different altitudes according to their long-adapted preferences. Some are confined to warmer lowlands; some thrive in the mid-elevations; others specialise in misty peaks.

Williams and his team have been monitoring 200 species, including birds, frogs, reptiles and mammals. The story they are starting to tell is of creatures chasing cooler conditions up the gradients, and becoming scarce when they reach their physiological limits or hit geographical ones – like running out of mountain. “Everything we predicted 10 years ago is starting to come true,” says Williams.

The lemuroid ringtail possum, Hemibelideus lemuroides, is among several creatures – including about 28 species of birds and at least three possums – showing noticeable declines or population shifts. A member of , it is named for its lemur-like eyes. These creatures are found in only two locations – above 1100 metres elevation in the Mount Lewis and nearby Mount Carbine range, and in the Atherton Tablelands about 100 kilometres south, where they have been found as low as 450 metres (see map).

Although both sets of lemuroids are thought to belong to the same species, white animals are extremely rare in the south, so anyone wanting to glimpse one has always come north, where they have historically made up about 40 per cent of the population. Nonetheless, given fears that the species is on the brink of extinction here, I know my chances of spotting a lemuroid of any colour in the next couple of days are slim.

Twenty years ago, when Williams was a PhD student, he would often drive up here with his university pals to look for wildlife. They might spot six lemuroids in an evening, which was already well shy of the 10 an hour students in the mid-1980s found. By the late 1990s and early 2000s, surveys were turning up fewer than one an hour on average.

Then there were none. From 2005 to 2008, Williams’s team clocked up around 150 hours surveying over 50 kilometres of Mount Lewis, flushing out not a single lemuroid. Meanwhile, surveys on the Atherton Tablelands had noted a shift in the southern population: more lemuroids were showing up at 1000 metres elevation, while they had disappeared from sites at 600 metres.

In 2008, Williams wondered aloud to a local journalist whether the northern lemuroid population might have already been wiped out. Happily this was not the case. After widening the survey areas, his team spotted a couple of individuals. However, as we set out on our hunt, there had been no confirmed sightings here since 2010.

“My gut feeling is that they got badly whacked in 2005,” says Williams. That year, summer temperatures were over 28 °C for 25 days running. “What happened since? I don’t honestly know.” Which is why we have come here, as an advance team for an intensive schedule of surveys.

The trick for spotlight surveys is to paint the forest with light. Keeping the beam fixed to your forehead or close to your eyes, you steadily sweep low to high, trying to ensure each 1-kilometre transect is walked at about the same pace. The wildlife spotted in each sliver of forest can vary greatly but the process gains integrity by repetition. The transects are walked again at dawn, listening for birdsong, and at midday, on the hunt for reptiles.

Surveying in the dark can be diabolical, navigating tree roots and rocks while craning to see the upper canopy. Shoulders ache from looking up. It is always damp, often foggy and sometimes pouring with rain. Leeches are an occupational hazard and will find their way into your boots, under your shirt, or behind your eyes. Despite it all, a rainforest by night is magical. There’s the flapping of the nocturnal birds and the chorus of frogs, some with a trilling ululation, others with a clunking plop, like a marble down a stair. And there are the eyes – sparkly emerald-green ones for the spiders, single bright spots of amber betraying geckos. Pairs of orange coals at ground level belong to frogs. Those staring down from the canopy will be a possum. With luck, it will obligingly freeze in the spotlight while the team confers about the species and notes GPS coordinates, conditions and behaviour.

“Leeches will find their way into your boots, under your shirt and behind your eyes”

One of our surveys on Mount Lewis is along the access road, so it’s a piece of cake. But three others are strewn along an overgrown logging route, dating from before . We spend an afternoon cutting through the undergrowth and the clinging wait-a-while vine with machetes. Mercifully we are too high up for the stinging tree, perhaps the most painful plant in the world.

We warm stew on a camp stove at sundown, then walk out in the dark. It is a punishing, 8-hour round trip with few sightings: six Daintree ringtail possums, three long-nosed bandicoots, two large rodents from the genus Pogonomys, a couple of frogs and a gecko.

On the second night we spot a gaggle of Daintree ringtails. In the past they would have been found in abundance lower down, but now they are occupying what used to be prime lemuroid country. There’s not a single lemuroid to be seen.

Lemuroids and other endemic Wet Tropics ringtail possums face a particular problem as the rainforest hots up. They live almost entirely in the high canopy and get their water from eating leaves. But those leaves also contain toxins, the forest’s defence against overgrazing, so hot possums have to weigh their need for fluid against the risk of poisoning.

Research by Andrew Krockenberger, also at James Cook University, indicates that the endemic . He says that unless they find a cool hiding place, four or five hours of this heat, especially repeated over several days, pushes them beyond their limits. The problem is amplified at Mount Lewis because poor soil makes it harder for the trees to grow leaves, so they value their foliage, lacing it with more toxins to protect from hungry possums. The cost-benefit ratio of grazing for hydration may be more acutely balanced here than on the Atherton Tablelands, where the soils are better and leaves less poisonous.

The lemuroid’s plight highlights the need to consider specifics when assessing the impact that climate change will have on a particular creature. In their 2003 paper, Williams and his team identified the (Cophixalus concinnus) as the most imperilled animal in the Wet Tropics. Their latest analysis uses more sophisticated models and . It gives the status of most vulnerable to the golden bowerbird (Prionodura newtonia) and puts the lemuroid possum in the top 10. “Assessments that include the biology of each species, rather than just pure climate predictions, really improve predictions about how vulnerable each species will be,” says Williams.

The updated results predict that the current carbon emissions trajectory will cause more than half of the region’s endemic species to become critically endangered or extinct by 2085. That is 24 per cent of all species in the vicinity. However, the models also indicate that this could be cut to just 2 per cent of all species if global warming were to decrease in line with the , under which greenhouse gas emissions stabilise by mid-century and drop thereafter. “[It’s] a reasonable, doable mitigation scenario,” says Williams. “And it would have a huge positive impact on biodiversity loss in this region.”

A month after our trip, Williams’s team returned to Mount Lewis for an intensive week looking for the lemuroid. They surveyed 20 transects and spotted 13 lemuroid ringtail possums, including three white ones. None were on the original survey sites; they were all in areas that had never been logged. “It seems that the possums hung on in the unlogged sites, although at such low numbers that we could not find them for years,” Williams tells me. “This could be very interesting, as it suggests that despite the forest structures not appearing any different now, the undisturbed forest had a greater resilience. Perhaps there were older trees with large hollows for the possums to find protection.”

These numbers suggest the abundance of the Mount Lewis lemuroids is back close to where it was before the 2005 heatwave. But such episodes are becoming more frequent and intense. For now, the white lemuroid lives on, although in nothing like the numbers once recorded. It seems that this possum, while an emblem of how vulnerable highly specialised rainforest creatures are, might yet provide some insights into nature’s resilience.

See more of the Wet Tropics’ finest in our gallery: “Imperilled possums of Australia’s Wet Tropics“

This article appeared in print under the headline “Ghosts of the rainforest”