A damning report has found several Australian ecosystems are so degraded; they are heading toward collapse if we do not intervene.
Of the 20 systems studied by a group of scientists, 19 showed evidence of a 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. Then,n 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
In February 1861, doomed explorers Robert Burke and William Wills spotted the waters of the Gulf of Carpentaria.
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.
“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 meter 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.”
While they might have been a curse to 19th-century explorers, we now know that mangroves are critical.
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 a drop in sea levels caused the big dieback of 2015, 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.
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
From the air, they look like the skin of a reptile or the bark of a tree. They’re endless rows of sand dunes, the gullies in between covered in low-growing, a scrubby tree from ground levels.
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.
Defined by the dominance of the gidgee tree — Acacia georginae — at a glance the woodlands appear arid and as good as lifeless.
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.”
The gidgee is a slow-growing, extremely hard-timbered tree that tends to dominate in the depressions between hills where water pools after rare rain events.
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 refugees 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.
Climate change forecasts predict fires to burn hotter due to longer, more intense dry periods and severe fire conditions, and the invasive buffelgrass exacerbates this.
Buffelgrass is favoured by graziers, but creates a higher fuel load beneath the gidgee that can result in hotter burns. According to Professor Wardle, the fear is that the gidgee itself will burn, leaving wildlife with nowhere to go.
“[We need] to be taking 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
The western central arid zones cover more than 40 per cent of Australia, stretching from the central Western Australian coastline, across to western Queensland and New South Wales, down to the Great Australian Bight and up into the central Northern Territory.
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.
Despite the harsh environment, the western central arid zones are home to some of our most iconic species — bilbies, thorny devils, inland taipans and dunnarts to name a few.
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.
“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.”
Like the Georgina gidgee woodlands, a combination of climate change, buffelgrass, and other invasive pests is also changing the fire regime.
“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 buffelgrass, 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.”