Until recently, a big old river red gum greeted people on the road that runs along the banks of the Murray River near the Walker Flat ferry crossing in South Australia.
"I looked at it every time I came off the punt," says Fiona Giles, spokesperson for the River Murray and Mallee Aboriginal Corporation.
The whitened trunk of the tree, which has been dead for some time, bore scars from slabs of bark that had been cut away and shaped into canoes by Fiona's ancestors.
But around six months ago, the tree suddenly collapsed and slipped into the river.
"My 73-year-old mum went down and tried to drag the river with a heavy rope with a weight on the end to try to feel it," Fiona says.
Fiona's mother and Nganguruku elder Jenni Grace wanted to recover the tree and put it up on Aboriginal land to preserve her ancestors' history.
"I always think how long that would have taken to chip with a piece of rock and with a wooden handle to get it off and make a canoe," Jenni says.
"That's the thing for me, thinking about how hard it would have been for the ancestors making that transport."
But although some people reported the tree had broken up and was floating down the river, Jenni couldn't find it.
'The water is not what it used to be'
Scar trees document the living history of First Nations people right along the Murray.
River red gums (Eucalyptus camaldulensis) were the tree of choice for making canoes, while the denser wood of the black box (Eucalyptus largiflorens) was used to make shields and coolamons to carry food.
But faced with declining water conditions and devastating drought, scar trees have suffered along some parts of the river.
Before European settlement, these trees lived through boom and bust cycles of flood and drought.
As the Australian colony grew, locks and weirs were built to stabilise water flows and support townships that sprung up along the Murray's banks.
They also enabled boats to travel along the length of the river as it meandered through broad flood plains, soaring red cliffs, and swamps to the sea.
While trees along the river banks had a year-round water supply, trees in permanently inundated areas died off, and those on higher ground were starved of water and salt built up in the soil.
"The condition of the water is not like what it used to be," says Jenni, who grew up travelling all along the river.
That's why Jenni and Fiona are part of the Living Murray Program, working with scientists to monitor the health of scar trees and water all along the river.
While some areas are still struggling, innovative water management programs are bringing life back to some billabongs in the backblocks of the flood plains.
"When the water gets delivered on Country, the whole thing just comes alive," Fiona says.
Spectacular seasonal cycles
River red gums mark out waterways across most of Australia.
As winter draws to an end, the red river gums on the Murray start to shed their bark.
In the right light they even appear to glow, says Susan Gehrig, an ecologist and ecophysiologist who studies the health of flood plains along the Murray.
"The bark hangs off the big trees like tinsel on a Christmas tree, and the fresh bark underneath is almost silvery white," she says.
It's part of the spectacular seasonal cycle on the flood plains.
"In a couple of months' time, the flood plains will look amazing when the pig face comes out and there's hot pink flowers under the eucalypts," Dr Gehrig says.
"One of the reasons I love the flood plains is they are dynamic."
River red gums have evolved to adapt to the ebb and flow of water, as long as it's not too dry or wet for too long.
When conditions are flush, the trees release seeds into the water en masse.
Smaller than a grain of sand, the seeds quickly send down a tap root as soon as the water recedes.
The strategy is to hit the groundwater as quickly as possible and anchor the tree in the soil.
They develop a fine network of roots in the upper soil, which will eventually make up the majority of the biomass and provide the bulk of water to the tree.
"If there is any part of the river where the sediment has worn away a bit, you can really see these strong root systems," Dr Gehrig says.
River red gums can grow up to 40 metres tall and measure up to 15m around their girth.
The trees are hard to age as they only put down tree rings in the good years, but it can take up to 150 years for a tree to develop the hollows that characterise its gnarly form and provide vital habitat for animals.
Monitoring vital habitats and scar trees
The mid to lower parts of the Murray River have a number of internationally significant wetlands on public and private land, which provide critical habitats for vulnerable and endangered animals like the regent parrot and southern bell frog.
"The flood plains were always meant to cycle through the boom phase of a flood back to the dry cycle," Dr Gehrig says.
"But if we stretch that dry cycle too long … then we are possibly getting away from what a good-condition flood plain should look like."
At the first sign of water stress, the trees become dormant, stop flowering, and shed their leaves. If they become highly stressed, they can die.
This is what happened during the millennium drought of 2001 to 2009.
The drought took an "incredible toll", says Kate Mason, an ecologist at the Murraylands and Riverland Landscape Board.
"It was a depressing time to work up and down the river."
While all the river was affected, habitats in the Riverland towards the border of South Australia suffered the most.
You don't need to drive far away from the river bank to still see the impact, Ms Mason said.
"You might be looking at trees with a girth that when it was alive, it was probably 500 years old."
Fiona and archaeologists from Flinders University documented the impact of scar trees on Calperum Station, a conservation area on Ramsar-listed wetlands just downstream of Chowilla.
They found that 80 per cent of the scar trees recorded had died or were dying.
"Because of European colonisation, there are few bark objects known from [the Riverland] region," says Amy Roberts, one of the study's authors.
"This is the only imprint we have of those objects going back in time."
Returning water to the flood plains
Following the millennium drought, state and federal governments started to look at ways to restore the water flows across some parts of the flood plain.
Although the trees can access groundwater, they get most of their water from the top part of the soil.
But the top part of the soil has become saltier in areas where the water table has risen, says Todd Wallace, a water ecologist at the University of Adelaide.
"The ground water in some areas is estimated to be 3 metres higher than it used to be," Dr Wallace says.
In the absence of regular flooding, increasing the flow back across the surface of the flood plain can help dilute the salt.
One way to do this is to raise the water levels in weirs by a few centimetres, so water flows up into the billabongs beyond the main channel, and then lower the water again.
A new system was also built on a side branch of the Murray that bypasses the main weirs and uses gravity to manage water across the Chowilla-Calperum flood plain.
Unregulated flows of water that are excess to economic use, as well as environmental water allocated by the regulator, are pumped onto smaller flood plains to create ephemeral wetlands.
Trees that were teetering on the brink can make surprising recoveries with a little water.
As their thirst is quenched, shoots appear from under their bark in the same way many eucalypts recover from bushfire.
It can take up to two years for the canopy to recover, and the tree starts flowering again. But there are no guarantees.
"We've seen some heartbreaking situations where we thought they were recovering, but it was almost a last puff of life," ecologist Ms Mason says.
"They put on this short burst of epicormic growth and then died suddenly, even with water at their base, because it was just too long between drinks."
But, she says, environmental watering programs offer hope.
"It does come with a price tag and it does come with a hunger for resources, but if we look at the do-nothing approach, the trajectory will be a decline.
"We are just trying to prevent so many areas from hitting that irrecoverable stage."
'We'll need to make some tough decisions'
While conditions are currently flush for the trees that live along the river banks and in low-lying areas, those further out still find it tough.
Environmental watering has been incredibly successful in areas of the Chowilla flood plain where water has been delivered, says Jan Whittle of the South Australian Department of Environment and Water.
But the water doesn't cover all of the flood plain.
"When we are operating … at full capacity, we can only get water to just under 50 per cent of the [Chowilla-Calperum] flood plain," she says.
"There is still a large proportion of flood plain that's kind of on its own, and would have once received a much more frequent inundation just with natural flooding in the river," she says.
Flows down the river currently exceed 50,000 megalitres per day, the most since 2016. But these are nowhere near the flood conditions needed to run right across the plains.
To do that there would need to be extensive flooding along the Murray as well as the Murrumbidgee and Darling Rivers, Ms Whittle says.
"We need more than 120,000 megalitres of water to get over that Chowilla-Calperum flood plain, and we haven't seen that since the 1970s."
But the flood plains will face even more pressure as climate change lengthens the gap between decent flood conditions and puts more pressure on the amount of water allocated for different uses along the river.
"It means will need to make some tough decisions," Ms Whittle says.
For now though, parts of the flood plain are flush with water.
And there are still some magnificent scar trees on the Chowilla flood plains if you know where to find them.
"I have my favourite scar trees," Fiona says.
One of the biggest she's ever seen bears a 2m-long scar down its trunk.
"It's massive, and the only way to get access to that tree is by boat.
"The bigger the scar is, you know that was a bigger canoe for a bigger family."
Three of the trees in our online poll — the river red gum, mountain ash, and snow gum — featured in a two-part Catalyst special exploring the lives of eight of Australia's oldest, largest and most distinctive trees. Watch now on ABC iview.
