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Decades-old mystery surrounding decline of ancient WA trees finally solved

*Photo credit: Kings Park

Twenty years ago, ancient trees in Perth’s Kings Park were in serious decline. For some unknown reason, their leaves began to yellow and ultimately drop, leaving bare trees slated to be felled.

While the reason behind this mysterious decline long eluded researchers, the underlying cause has not only been uncovered, but a pretty straightforward means of rectifying the issue has also been developed.

Ultimately it was data collected by scientists between 2003 and 2006 that finally shed light on the situation.

As it turns out, the iron-rich bore water used in the irrigation of buildings and other forms of infrastructure such as parks was the catalyst for the problem. Because the iron in the water was eating away at the irrigation pipes, more additives were put into the water. When this water reached the park, that was a problem for the trees.

“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,” Manager of horticultural development at Perth’s Kings Park Partick Courtney said.

The term ‘chlorotic decline syndrome’ was coined because the trees had stopped producing chlorophyll – the green pigment found in tree leaves that enables photosynthesis … or the production of sugars by using energy provided by the sun.

This process is essential to provide trees with the energy they need to live, grow and thrive.

Researchers started to water the areas around some of the affected trees with a slightly acidic solution in an effort to lower the pH of the surrounding soil. The results were highly encouraging!

“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.”

The researchers then faced the task of ensuring the hundreds of thousands of plants and trees throughout the park could be adequately treated in the same way. It was clear a massive infrastructure project would be needed.

“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.

The breakthrough has potential implications extending well beyond the parameters of Kings Park, with the results set to be shared around the world to support the maintenance of health urban forests globally, long into the future.

Source: ABC

Posted Date: July 17, 2023

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