It appears someone has used a small axe or a machete to fell the trees, five of which were about 15m tall, had a half-metre girth and were more than 60 years old.
Dunedin City Council parks officer Scott Maclean said staff were appalled by the sheer scale of the damage and bewildered by the degree of persistence and motivation required to achieve it.
"It would have taken them hours to do one, but to do five? It's a pretty boring way to spend your day."
The five mature trees and eight younger ones, all different types and in close proximity to each other, remain where they fell in dense bush, about 50m from any road and the same distance from houses below the Town Belt.
"It's not someone trying to expand or clear their property."
Mr Maclean said council staff were deeply upset about the damage.
Such serious cases of vandalism were rare, he said.
The destroyed trees were discovered by a possum contractor carrying out routine work in the Prospect Park area of the Town Belt.
They appear to have been felled some time during the past two to three weeks.
Staff had referred the matter to police, and were also determined to find those responsible.
They urged anyone with any information, or who heard any chopping from the Town Belt, to contact them.
Letters would be sent to neighbouring residents seeking the same information.
Anyone with information about the vandalism should contact Martin Thompson (Parks and Reserves team leader) or Scott MacLean on 477-4000.
