Jersey Trees for Life says the 40ft tall trees at Mont à l’Abbé were damaged last weekend.
The charity, which works to protect trees across the Island, claims the attack could have been committed by a nearby resident, following a long-standing dispute.
Gerard Farnham, the charity’s chairman, said: ‘We think it could have been a local resident. We don’t want to point fingers but it is definitely vandalism, it’s criminal damage.
‘The police have been informed now so we hope they take action.
‘The trees have been massacred. So much damage has been caused, it has made them unsafe.
‘A lot will need to be spent now to make them safe.’
He added: ‘With the damage caused they will probably fall ill and they will be diseased so eventually the tree will just end up dying.
‘The cost will be into the thousands and someone will have to pay for that.’