Three peaks in three weeks
Climate change in Australia’s tropical cloud forests.
An AGS-supported trip to Queensland’s cloud forests
TORCH BEAMS SCYTHE through the gloom, painting the underside of the rainforest canopy above us with bright white light. Insects buzz, click and hum, frogs croak and creak and tiny bats emit high-pitched squeaks as they flutter erratically past. We’re deep in a dense tropical jungle but the night air is cool and moisture drips from thick moss on the trees and rocks.
No-one speaks. We’re all weary, having spent several nights trudging more than 50km along forest transects searching in vain for our quarry, the rare white form of the lemuroid ringtail possum. Then, finally, a torch beam comes to rest on a big, fluffy white ball, perched on a branch high in the canopy. Bright-pink nose, large, dark eyes, the possum gazes down at us, apparently wondering what all the fuss is about.
We’re elated, but the sighting is bittersweet. Climate change has brought this icon of the Wet Tropics to the brink of extinction, and as we return its gaze we can’t help wondering how much longer this beautiful creature will persist in these forests.
WE’RE HIGH ON MT LEWIS – an oasis of cool in tropical north Queensland, and one of the few places in which the white lemuroid possum can be found – as part of an expedition to climb three of Australia’s highest tropical
mountains in three weeks. With support from the Australian Geographic Society, our team of researchers and adventurers is hoping to gain insights into how climate change is affecting the unique plants and animals inhabiting the mysterious cloud forests that drape the summits of these three peaks.
The rainforests of the Wet Tropics are among the world’s most ancient ecosystems. They’re the largest remaining remnants in Australasia of the great rainforests that covered the supercontinent of Gondwana 100–50 million years ago.Although they make up a relatively small proportion of Australia’s total land area, they have the continent’s highest levels of biodiversity and endemism.
Like isolated islands in this vast ocean of rainforest, the mountaintops of Mt Bartle Frere South Peak (1622m),Thornton Peak (1374m) and Mt Lewis (1224m) sit high above the surrounding lowlands. And, just like many true islands, the summits of these peaks are home to numerous species found nowhere else, from tiny frogs whose offspring hatch fully formed from eggs, eschewing the tadpole stage, to a lizard said to be so heat-sensitive it will die if held in your hand for too long.
These mountain tops are also home to some of Australia’s cloud forests (see box, page 119), gardens in the sky with all the beauty and diversity of their lowland counterparts without the oftenoppressive heat.Tendrils of mist float among trees draped in living cloaks of epiphytes. Moss and lichen grow on every available surface and ferns sprout from unlikely spots on ground and trees alike.
Sadly, cloud forests are among Earth’s most endangered ecosystems. Tropical species are inherently vulnerable to environmental change because they tend to be rare and occupy small ranges. And, because tropical environments are usually relatively stable, the species that inhabit them can often only survive within a narrow range of climatic conditions. The mountain-top specialists are especially vulnerable because they’re adapted to the cooler, wetter conditions found on summits.As the climate warms, these conditions disappear, so, if species can’t move or adapt in time, their demise is inevitable.
Long-term monitoring data have already pointed to significant changes in the distributions and abundance of many bird and mammal species in theWetTropics, with upland endemics having undergone the most significant declines. The lemuroid possum is a case in point. Research by Professor Stephen Williams of
James Cook University (JCU) in Townsville during the past 10 years has shown the possum is becoming increasingly rare. The main reason for its decline is the increase in the intensity and length of heatwaves in the Wet Tropics. In the summer of 2005, maximum temperatures were above the possum’s physiological tolerance for 27 days in a row.With nowhere for the possums to go, many succumbed to the heat, causing the population to crash.
THE FIRST OF OUR ‘three peaks in three weeks’ challenge isThornton Peak, about 90km north-west of Cairns. Rising sharply from surrounding lowland rainforest, it’s a beacon dominating the tourist drive from Cairns to the Daintree rainforest, its jagged apex often hidden by cloud and mist.
Reaching our campsite just below the summit involved 12 hours of bashing through dense jungle, scrambling ever upwards along a steep, barely visible trail. Then, suddenly, we burst from the dark forest onto a jagged ridge. Just a few hours before, 1000m below, we were sweating in the hot, humid sauna of the lowland rainforest that surrounds the mountain’s base. Now, as we stand exposed on a series of large granite boulders, blasts of cold, mistladen air sweep over the ridge, chilling us to the bone.
Our team of seven scientists and adventurers is hungry and exhausted but in good spirits, having made camp before nightfall. In the fading light, between breaks in the clouds, we glimpse the mountain summit we’ve come to explore. Our surroundings seem enchanted and other-worldly.The eerie, mysterious atmosphere hints at the biological riches hidden here in this unique environment.We have four nights to explore the area and hopefully track down some of the species found only on this peak.
Around us, the forest is alive with the sounds of crickets, frogs, and a trickling permanent creek that runs past our camp.Among the cacophony, tropical ecologist Nadiah Roslan makes out the call of the critically endangered beautiful nursery frog – one of our primary targets. Found only on this peak above 1100m, it has one of the most restricted ranges of any frog in Australia; the total area of suitable habitat is estimated to be little more than 700ha – a third the size of the City of Sydney local government area.
Species such as this are most at risk from climate change because they’re the least able to adapt or move elsewhere. They’re also more sensitive to climate change. Steve explains: “Amphibians,
The eerie, mysterious atmosphere hints at the biological riches hidden here.
reptiles and invertebrates are particularly vulnerable because they are already close to their limits of temperature tolerance.”
TheThornton Peak skink is another example. Recorded from only a few localities atop this mountain, the species can only handle a very narrow range of conditions and it, too, is on the brink of disappearing.
OUR NEXT DESTINATION is Mt Lewis, 50km south of Thornton Peak. As well as hosting the white lemuroid ringtail, its upper reaches are home to the bright blue and red Mt Lewis spiny crayfish, one of six freshwater crayfish species found in theWetTropics. Living in cold, fast-flowing streams, these crayfish are only found above 800m. Each mountain range has its own species, although all are believed to have come from a common ancestor that expanded its range into Queensland more than 5 million years ago, when temperatures were cooler and rainforests more extensive.With natural climate change came a contraction of forest habitat, resulting in different mountaintop populations separating and evolving into different species.
Our third and final peak is Queensland’s highest. Mt Bartle Frere is among the state’s most popular hikes, but when you’re loaded with camping and survey gear it isn’t for the faint-hearted.To make matters worse, in contrast to conditions on our other ascents, the day is hot, dry and still.As we climb, it becomes clear it has been
like this for some time.The dripping mosses and ferns that clung to trees and rocks on the other peaks are dry and brown here and leaf litter crunches loudly beneath our feet. Such conditions are a brief glitch for a mountain with one of Australia’s highest rainfalls, but a timely insight into what may lie ahead for these cloud forest communities as dry periods become more frequent.
After an eight-hour slog, we reach the summit and are rewarded with clear skies and stunning views.As we explore the forest near our camp, a brilliant golden shape suddenly flashes before us. Like a scene from a Harry Potter film, a strikingly coloured male golden bowerbird appears, as if from nowhere, watches us curiously for a moment, then flits off through the dappled light of the forest.
As a high-altitude forest specialist, this bowerbird is another species that’s undergone a recent decline in distribution and numbers. We follow it as best we can, fumbling through the undergrowth, and eventually stumble across a large, elaborate and rather incongruous structure. Before us stands the male’s majestic bower, an elaborate construction of two towers well over a metre tall, made from a tangle of twigs and adorned with grey-green lichens, flowers and fruit. Males build and tend these constructions with great care, using them to attract and woo females.
THE TROPICAL ZONE’S importance on the global stage is increasing. By 2050 most of the world’s people, including almost two-thirds of its children, will live in the tropics. Tropical nations are also developing rapidly. These tumultuous changes, overlaid by the impacts of climate change, suggest that what happens in the tropics in coming decades will have significant global implications.
While polar bears and melting ice caps are often used to highlight the impact of climate change on the natural world, it’s clear that some of the most significant effects are being felt in the tropics. Because this region hosts most of the world’s cultural and biological diversity, there’s also much more to lose here. Perhaps, then, the white lemuroid ringtail possum or golden bowerbird would make better flagship species for highlighting the impact of climate change – they’re certainly closer to extinction.
Members of the scientific survey team hike through alpine grasslands near the summit of Thornton Peak.
The survey team takes a break among the boulders and mist high on top of Thornton Peak. (L–R) Ashley Smith, Dr Paul Thuesen, Dr Malcolm Brown, Dr Dean Miller, Nadiah Roslan and Ben Flynn.
This rare white form of the lemuroid ringtail possum is found only above 1000m at a few sites in the Wet Tropics. This one was spotted on top of Mt Lewis.
A male golden bowerbird decorates its elaborate bower with fine, small flowers on Mt Lewis.
The beautiful nursery frog, a tiny ground-living species in the family Microhylidae, is only found in rainforests above 1100m on Thornton Peak. It has one of the most restricted ranges of any Australian frog.
Expedition leader Dean Miller takes in the view across a valley near the top of Thornton Peak.
Biologists Scott Harte, Nadiah Roslan and James Donaldson (L–R) inspect a camera trap used to survey wildlife on Mt Lewis.
Spectacular red and blue Mt Lewis spiny crayfish inhabit the cool, clear mountain streams of the three peaks. They can reach up to 30cm in length and live for more than 10 years.
Forests at the top of Thornton Peak (see bottom) look more at home in a Tolkien-style fantasy than in the tropics of northern QLD, and of all the peaks surveyed, Thornton seemed the most other-worldly. Mosses adorning trees (left) extract moisture from the air, driving the cloud forest system.
A sunset view south from Mt Bartle Frere, the highest mountain in QLD. During our expedition here the peak was warm and dry and provided insight into how these peaks would look if temperatures continue to rise and the cloud forests decline.