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| Australia's arid zones are harsh, but home to some of our most
iconic species. ABC: Caddie Brain |
Of the 20 systems studied by a group of scientists, 19 showed evidence of collapse in some areas and required "urgent action" to prevent them from undergoing total collapse.
Ecosystem collapse is what happens when a system is so fundamentally altered that it completely reorders, often resulting in a less diverse group of plants and animals and interactions between them than before.
Among those identified in the report in Global Change Biology were some very well-known ecosystems — the Great Barrier Reef, the Murray-Darling Basin, Ningaloo Reef and Far North Queensland's tropical rainforests.
But then there were the less well-known habitats like the Georgina gidgee woodlands, the western central arid zones, and the Gulf of Carpentaria mangrove forests.
So, what are some of these less-well known and arguably less glamorous Australian ecosystems at risk, and why should their decline concern us all?
Gulf of Carpentaria mangrove forests
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| Mangroves in the Gulf of Carpentaria are vital for prawn and fish
stocks. Getty Images: Elizabeth Barnes |
But despite travelling more than 3,000 kilometres from Melbourne, they never made it to the coastline, thwarted just 10 kilometres from their destination by impenetrable mangrove swamps.
One hundred and sixty years later, the decline of those mangrove swamps has scientists worried.
Today, just to the north of the explorers' turnaround point, is Karumba, the site of an 80-square-kilometre mangrove dieback that surprised and baffled scientists in 2015.
Rising sea levels due to climate change are increasingly known to kill mangroves.
But the researchers were shocked when they discovered the reason why the mangroves died, said Norman Duke, a mangrove ecologist at James Cook University and one of the report's 38 authors.
It wasn't the first time a severe dieback had occurred in the Gulf — it had also happened in 1982, but had gone unnoticed.
"That's important, because 1982 and 2015 were the two most severe El Nino events on record," Dr Duke said."Those events, to the surprise of everyone including me, caused a drop in sea level."
El Nino events cause a breakdown in trade winds. Combined with changes in regional climatic conditions, that causes sea levels in the western Pacific, including around Australia, to drop, while they rise in the eastern Pacific.
"In the Gulf of Carpentaria and other places across northern Australia, the [sea level] drop was half a metre in 2015. That half a metre prevailed for five to six months," Dr Duke said.
"So that means that the mangroves in [the Gulf] where it doesn't rain very much didn't get water and died of thirst."
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| The mangrove dieback was cause by a drop in the sea level during
an intense El Nino. Supplied: James Cook University |
In the Gulf of Carpentaria, they provide structure to the coastline and are the habitat for juvenile prawns that stock part of Australia's largest prawn-producing region, the northern prawn fishery.
They're also the breeding and nursery grounds for numerous fish species, including barramundi and mangrove jack, as well as mud crabs.
And they sequester what is known as blue carbon. Unlike terrestrial plants that only store carbon until they decompose or are burnt, mangrove leaves and branches are buried in sediment that locks away their carbon stores, potentially for aeons.
While the big dieback of 2015 was caused by a drop in sea levels, the longer term threat is rising sea levels, according to Dr Duke.
But because mangroves are fairly fast growing, in the Gulf they're showing signs of adapting to the trend of sea-level rise, he said.
"They're doing what they're supposed to do, which is growing or walking up the profile [while] the ones at the sea edge are dying and being washed away," he said.
"If it happens holus-bolus as it has with this massive dieback, the whole shoreline gets this widespread erosion."Climate change models predict El Nino events to intensify, Dr Duke said.
But beyond efforts to combat climate change, the best thing we can do is provide the space for mangrove systems to retreat.
In the Gulf, where the coastline is sparsely populated, that includes managing feral pests that destroy the new growth, Dr Duke said.
"The best way we can help is to contain the pigs and the fires and threats to mangrove retreat."
The Georgina gidgee woodlands
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| The surrounding yellow grassland has been burnt out, with the
unburnt gidgee providing refuge for fleeing wildlife. Supplied: Google Earth |
The Georgina gidgee woodlands are scattered across a vast, almost circular expanse of the south-eastern Northern Territory, into western Queensland and northern South Australia.
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| The Georgina gidgee woodlands have a widespread distribution in the
centre of Australia. Supplied: Glenda Wardle |
But dig a little deeper and they're not only diverse, but play an extremely important role in the central Australian ecosystem, according to ecology and evolution expert Glenda Wardle from the University of Sydney, who also contributed to the report.
"There are 81 bird species that use these woodlands. Some use it for nesting and others use it to travel through the landscape," Professor Wardle said.
"And there are a range of mammals and reptiles as well."
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| Gidgee trees tend to grow where water pools after rare rain
events. Supplied: Mark Lithgow |
Partly because the timber is so hard, it doesn't usually burn during the region's periodic grass fires, Professor Wardle said.
Instead, when fires sweep the area, the gidgee provides shelter for animals like red kangaroos, small marsupials, native rodents and bats.
"What makes them special is that they're refuges post fire and post drought," she said.
"Fires over time are recurring [about] every 26 years. During those fires, the areas of the Georgina gidgee woodlands don't burn so easily and they act as refuges for species — this is where fauna is retreating to."
But the woodlands are under threat from climate change, pests and overgrazing.
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| Pests including camels are doing a lot of harm to the Georgina
gidgee woodlands. Supplied: Glenda Wardle |
Buffel grass is favoured by graziers, but creates a higher fuel load beneath the gidgee that can result in hotter burns.
The fear is that the gidgee itself will burn, leaving wildlife with nowhere to go, according to Professor Wardle.
"[We need] to be making action on climate mitigation in Australia … without that, everything else will just be fiddling at the edges," she said.
But alongside climate mitigation, she said efforts to preserve the Georgina gidgee woodlands need to focus on getting camel numbers down and managing stock in sensitive areas.
"Underneath the gidgee itself, cows remove all vegetation, all habitat, and all other species, so the adult trees can't [reproduce]," Professor Wardle said.
"The other thing is camels — camels browse on these trees."
Without intervention, researchers like Professor Wardle predict that the system will "cascade into desertification".
Western central arid zones
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| The western central arid zones encompass a vast and environmentally
diverse area. Getty Images: Ted Mead |
The vast area is characterised by low and episodic rainfall, flat terrain and vegetation spanning low, open woodlands and shrublands, to grasslands, rangelands and desert dunes.
Perhaps because of its seemingly endless plains, the rare changes in elevation in the arid zone — Uluru, Munga-Thirri-Simpson Desert, Tjoritja-West Macdonnell Ranges, and Kati Thanda-Lake Eyre — are some of our most revered landmarks.
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| The western central arid zones are home to some of our most
iconic species, including bilbies. Supplied: Brad Leue, Australian Wildlife Conservancy |
But again, researchers have warned that the bioregion is facing collapse and climate change is the greatest existential threat, according to Suzanne Prober, a senior research scientist with the CSIRO and report co-author.
"What is extraordinary is when you go out and you see the mulga dying. Mulga is one of the toughest trees in Australia, it just keeps on keeping on," Dr Prober said."It's not dying due to fire, it's just the leaves are dead. I've been getting other reports from all over the place. There are patches of mulga dying in the Gibson Desert and that's way out of the range of livestock grazing."
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| Buffel grass changes the fire regime and is wiping out mulga
trees, researchers say. Supplied: Suzanne Prober |
"The Great Victoria Desert supports these marble gums all over the desert, but there are just huge landscapes where the fires are killing the trees," Dr Prober said.
But it's not too late to make changes that can help turn things around, according to wildlife ecology expert and report co-author Euan Ritchie from Deakin University.
"We're trying to highlight that yes, things are grim, but it isn't too late. Yes, we can act," Professor Ritchie said.
A "major biological control program" to stop the spread of buffel grass, protection of freshwater refuges from weeds and livestock, cool-burning fire management, and the control of pests like feral cats and camels can all ease the pressure these systems are facing.
According to researchers like Professor Wardle, if we don't intervene to help these systems recover, we'll find out they're not just iconic, but they're quite literally holding the country together.
"If the degradation [we reported] goes to the worst extent, the 2009 dust storm that swept across Australia is the starting point," she said.
"That's when we'll remember we live in a red country."
Links
- These waters at the bottom of Australia are warming up to four times faster than global average
- 'We can raise a red flag now': 2019 the second-hottest year on record for Earth, WMO says
- Bushfires could kickstart a new crisis for Australia's rivers
- The ingenious tricks animals have found to outsmart bushfires
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