Five pōhutukawa trees at Pukeahu National War Memorial Park in Wellington have been vandalised.
Some of their branches have been broken and their bark stripped.
They were planted to commemorate the 100th anniversary of World War I.
Wellington City Council's arborist team said they were monitoring the trees but despite efforts, they would likely die.
It said the trees would need to be replaced at a cost of up to $400 each.
The council said it was keeping an eye on the area and working with the Ministry for Culture and Heritage, while police and local host patrols would be increased in the park.
If you spot anyone damaging trees in the city call WCC on 04 499 4444.