Vandals have cut down or damaged up to 75 trees in Dublin's Dodder Valley Park causing damage of around €33,000.
Mayor of South Dublin Alan Edge described the destruction as a bizarre, targeted act of vandalism.
A spokesperson for South Dublin County Council told RTÉ News that 25 mature trees were cut along with 50 saplings.
Council workers are in the park assessing the full scale of the damage, estimated to be around €33,000.
This cost is based on the value of buying new mature trees and replacing the saplings and it does not include clean-up or staffing costs, the council said.
Speaking on RTÉ's Morning Ireland, Mr Edge said it is believed the attack happened between Friday night and Saturday morning.
He said the destruction was planned and must have taken "quite some time to get through so many trees".
"So someone has presumably charged up their electric saw, gone to the park in darkness and spent some considerable time taking down these trees...it's bizarre that somebody would go to such lengths," he said.
"The council have put huge investment into it, but community have as well.
"We've had community groups planting trees. They planted, I think 16,000 across the county, over 8,000 in Dodder Valley Park."
People have been left reeling and "really, really disappointed", the independent councillor said.
In a statement South Dublin County Council said it was "extremely disappointed" at the act of vandalism.
"The Council is evaluating the scale of the damage and the incident is under investigation by An Garda Síochána," the council said.
"We urge members of the public to come forward with any information they may have regarding this incident and to report such information to the gardaí.
"Once a comprehensive assessment of the damage has been completed, we will issue a further statement detailing our response and plans for restoration."
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