City park maintenance workers found the vandalism and it has been reported to the Department of Environment Regulation.
The trees are a species known to provide habitat for the endangered Carnaby’s black-cockatoo.
One of the trees was left lying across a footpath and recently built stairs to a beach path.
The city is now considering replacing the trees.
Anyone with information can call DER on 1300784782.
The maximum penalty for an individual illegally clearing native vegetation is up to $250,000 or three years’ jail.