Key Points:

One of the New Zealand's most famous trees has had its top knocked out in this week's storm, shortening its life by hundreds of years.

The rata tree that was growing from the centre of kauri tree Te Matua Ngahere in the Waipoua Forest, north of Dargaville, was blown to the ground.

It took with it the central leader of the kauri and several of its branches.

Waipoua Forest Trust conservationist Stephen King said rata trees grew on older trees, sending roots to the ground and eventually taking them over.

"But when you look up at it now you just see sky, no canopy."

Forest workers noticed the damage yesterday morning but believe it happened on Tuesday night.

Te Matua Ngahere, estimated to be between 2000 and 3000 years old, has the biggest girth of any tree in New Zealand, about 7.6m. At 208 cubic metres, its trunk is the second biggest by volume.

Tane Mahuta, also in the Waipoua Forest, is bigger at 244cu m. "To anyone who hasn't seen [Te Matua Ngahere] before, it's still as grand as ever," Mr King said.

"People go to Europe and see castles that are 1300 years old. This guy is more than 2000 years old. He really does look like the father of the forest."

Mr King said kauri trees had been known to live about 4000 years but Te Matua Ngahere's damage might have knocked about 300 years off its life.

"It's still alive though. This is our heritage. New Zealanders will drop in on their way up north and say 'Gidday' to Tane Mahuta and Te Matua Ngahere. It's our identity. It will continue to inspire many people to come."

Mr King said Te Matua Ngahere had about 50 plant species growing on it as well as the rata.

He said the storm had made it easier for scientists to study the tree's ecology as they could take samples of the fallen wood and plants.

Mr King estimated about 50,000 domestic and international tourists would see Te Matua Ngahere a year.

"It is fondly appreciated.

"When you look at him he has such a sense of presence."

Kaumatua of the forest Davey Paniora, 67, from Northland's Te Roroa iwi, has worked in the forest since he was 15.

"It looks pretty bad. It's sad to see [the tree] like that after all these years." He said weather had never affected the tree in his time there.

"It's just happened so we're all pretty shattered, but I'm sure as time goes on things will get back to normal."