But Ms Lilley said the palm had been subject to "dramatic vandalism".
"At the time it was decided to monitor the tree to see whether its condition changed as a result of this cutting. I've inspected it a couple of times and on the last inspection it showed recent vertical splits on both sides of the tree. This is obviously a significant weakness, and the tree is very likely to fail," she said.
She said the palm, at the southern end of the park near the intersection of Anzac Parade and Georgetti Rd, could either fall on to the highway or on to the public walkway, and that was why it had to go.
Ms Lilley said with broadleafed trees, pruning can sometimes mitigate risk, but pruning could not be done to this palm because all the leaf growth is at the top.
"I don't believe a man-made structure will provide a safe, long-term future for this tree.
"While it's one of the older trees in the park, it isn't rare and there are several young Washingtonias growing nearby."
She said removing mature trees was always a difficult decision to make, "however a realistic approach has to be taken and the tree will not recover".
"In my professional view it's highly likely to fail, and it's better to remove it and allow the other trees nearby to fill in the space," she said.