Around 2003, the trees in Perth's Kings Park started to decline — their leaves yellowed and began to drop.
Some of the trees, which are hundreds of years old, were left bare and had been slated to be cut down.
It took scientists decades to figure out what the problem was and then discover the relatively simple way to solve it.
Those ugly but all too familiar bore stains
Manager of horticultural development at Perth's Kings Park, Patrick Courtney, said data that scientists had collected between 2003 and 2006 revealed the cause.
The problem had to do with those ugly but familiar stains seen on buildings and infrastructure irrigated with iron-rich bore water.
The iron was also eating away at the irrigation pipes.
In the 1990s, additives were put into the bore water being used to irrigate parks and ovals to stop those stains.
"We had made the water more alkaline and trace elements that are vital for plants were no longer available and our trees were suffering from this inability to take up these important trace elements," Mr Courtney said.
They coined the term chlorotic decline syndrome — because the trees stopped producing chlorophyll and therefore could not function efficiently.
In 2006 they began trials to lower the pH of the soil around some of the affected trees by watering them with a slightly acidic solution to see if they could reverse the decline.
What they saw was surprising.
Tree canopy renewal
"We saw in trees that were at the point where they were going to be removed and had no canopy left, we could actually change pH and the trees would transform," Mr Courtney said.
"Within six weeks they would start growing a new canopy and at that point, we knew what it was and we knew we could reverse it."
Research scientist with Kings Park Science, Emily Tudor, said the research legacy leading up to that discovery was significant.
She has spent years collecting data including the transpiration rate, electron transport rate, stomatal conductance and photosynthetic efficiency in leaves of different species of plants in the park.
"We use machines that give you a rapid response insight into how that leaf is performing in the moment.
"Capturing that across time, before and after treatments, is how we understand the response of a tree to our treatments."
Ms Tudor said seeing that a tree had put on new, green growth was just one part of the puzzle, but having the scientific data to back it up was hugely important.
"Understanding cause and effect relationships is critical to management and having evidence-based insight into how to treat these things," she said.
Race to treat on a larger scale
The team then faced a big task — how to treat the hundreds of thousands of plants and trees in the park.
"How can we do it across a whole landscape was the big challenge," Mr Courtney said.
"A lot of advice was that we wouldn't be able to do that."
The park embarked on a big infrastructure project.
"At the treatment plant we're bringing in the bore water, the first stage is the iron removal and then we'll adjust the pH through a complex system that actually micro doses the water with acid," Mr Courtney said.
"So all of our primary water that goes out into the park into the irrigated landscapes will now be at a better pH for the health of all the plants in the garden.
"We have a representation of all of the state's flora by geographical regions and there are so many plants that grow on acid sands or acid soils.
"This change we're making at Kings Park will bring back all of those really amazing species and allow us to establish them much more easily."
Securing urban forests for the future
It's a solution that extends far beyond the reaches of the park.
"It's not just us who are experiencing it here, it's applicable to urban landscapes, it's applicable to the state domestically and internationally as well, it's certainly a widespread issue," Ms Tudor said.
The team will share the results of their studies around the world.
"What we do now means that in 50 years time with climate change, we'll still have amazing urban forests within our city, so it's really important," Mr Courtney said.
