It's called "the escalator to extinction": as mountain habitats are warmed by climate change, resident plants and animals are continually forced upslope until they simply run out of room.
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Scientists the world over have long feared the impact of such events but now concede it's actually happening across one of the planet's most spectacular rainforest regions, in far north Queensland.
Researchers Stephen Williams and Alejandro de la Fuente have just completed an assessment of bird populations in the Australian Wet Tropics World Heritage Area, stretching 650 kilometres from Townsville to Cooktown.
Examining the abundance and distribution of 42 species, they found compelling evidence that as temperatures rise, lowland birds are moving uphill and displacing other species.
Birds that live at high altitudes along the rugged coastline - most of them rare upland species - have been pushed out of the lower levels of their ranges, with their numbers declining by almost half.
Meanwhile lowland bird populations in the same areas have increased 190 per cent.
With data collected over 16 years from 114 sites between sea level and 1500 metres, the James Cook University pair say their findings suggest a bleak outcome.
"The outstanding universal value of the Australian Wet Tropics World Heritage Area, one of the most irreplaceable biodiversity hotspots on earth, is rapidly degrading," they say.
"These observed impacts are likely to be similar in many tropical montane ecosystems globally."
Worldwide estimates of extinctions over the remainder of the century as a result of climate change suggest potential losses of between 15 and 35 per cent of all species.
The projected impact is expected to be especially severe in mountain ecosystems with more than 80 per cent of species facing high extinction risk.
The global significance of montane ecosystems is heightened in the tropics, with approximately half the world's species of plants and vertebrates believed to be endemic to 34 identified global biodiversity hotspots.
Professor Williams and Mr de la Fuente say bird species will especially continue to experience upslope shifts.
"Left with nowhere else to go, montane species are predicted to become increasingly susceptible to stochastic extinctions or declining populations," they say.
"This so-called escalator to extinction has been predicted, and now observed, in a number of places and taxa around the world."
Australian Wet Tropics rainforests were World Heritage listed in 1988 and are described as the planet's sixth-most irreplaceable protected area.
They are home to 370 bird species, 11 of them - including the endangered southern cassowary - found nowhere else.
Nine of the endemic species are confined to upland rainforests.
They include the tooth-billed bowerbird, golden bowerbird, bridled honeyeater, fernwren, Atherton scrubwren, mountain thornbill, grey-headed robin, northern logrunner and Bower's shrikethrush.
Australian Associated Press
