The Department of Conservation (DOC) today admitted it made a "bad mistake" when it chopped up some ancient rimu trees for firewood on Stewart Island private land.

Lindsay Lord, who owns 180ha on the island, was horrified when he discovered the native trees -- estimated at between 450 and 600 years old -- had been sliced into rings.

"It was a waste of a beautiful resource that is in much demand -- just to chop it up for firewood, I was dismayed," Mr Lord, 75, told NZPA.

DOC is now considering compensating Mr Lord for the timber because it precluded him milling it for his own use or selling it.

Part of the island's Rakiura Track runs through Mr Lord's property and three trees had blown down in a storm and were blocking it.

Mr Lord found the huge rimu slices stacked by the track last weekend and confronted Stewart Island DOC staff, but was told they knew nothing about it.

However, DOC Southland spokesman Greg Lind confirmed to NZPA today that DOC had made the mistake.

Staff often cut up wind-thrown trees for firewood to use at the track's huts, he said.

"The decision was made to utilise two trees for firewood and then helicopter it to a hut. The person in charge forgot the land was private."

The giant rimu, which had stood about 25m-tall, took a day to slice up and would have supplied the hut for a year.

"Normally, we would contact the owner and ask them what they wanted to do about the trees -- but now Mr Lord's trees are in pieces and he can't do anything with them," Mr Lind said.

"We had no permission to remove firewood, nor should we have whacked through some very large wind-thrown trees without asking Mr Lord first -- we overstepped the margin and he was quite rightly angered by that."

DOC was considering compensation and was in contact with Mr Lord, Mr Lind said.

He said DOC had had a "vigorous" relationship with the Stewart Island community over the use of aerial 1080, the running of Rakiura National Park and marine reserves.

"Most of those issues have been laid to rest through good community discussion," he said.

About 90 per cent of the island is administered by DOC, 8 per cent by the Rakiura Maori Land Trust and the rest is privately owned.

Mr Lord owns one of the few pieces of private land that has never been logged, with an original canopy of rimu.

About 30 of his family members periodically visit the land and he invites schools and other groups to visit.

"I was a bit annoyed that I've been involved here for about 40-odd years but DOC staff didn't ring me or duck up the road and see me before doing this -- it was a case of ignorance on their part," he said.

"I want a fool-proof system to make sure this does not happen again."

However, he said he did not want DOC staff censured as "everyone makes mistakes".