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.