Volunteers plant seeds for towering eco-system in north Christchurch

Wednesday, 25 August 2021

Behold a kahikatea seedling. Almost 40,000 of these have been planted in north Christchurch.

There’s something almost spiritual about planting a kahikatea tree.

The seedling could grow 55 metres high and still be alive in 450 years or maybe 750 years. Some say 1000 years.

Now realise that almost 40,000 kahikatea trees have been planted in Mairehau, north Christchurch.

All going well, there will eventually be an immense forest here, a towering ecosystem that’s about two hectares larger than Pūtaringamotu/Riccarton Bush and populated with pīwakawaka (fantail), tauhou (silvereye), riroriro (grey warbler) and kererū (wood pigeons).

People enjoy the sunshine at Riccarton Bush in Christchurch.

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Pigeons come in to roost on one of the highest trees at Riccarton Bush in Christchurch.

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Hamish Fairbairn of Conservation Volunteers NZ crouches among recently planted kahikatea seedlings in north Christchurch.

That will take time, but kahikatea grow fast early in their lives. Some will be 5m high after eight years and some 10m high after 15 to 20 years, Christchurch City Council head of parks Andrew Rutledge said.

There is not a consensus on how tall or how long kahikatea will grow.

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“This is for our children, great-grandchildren and great-great-grandchildren to enjoy,” said Hamish Fairbairn of Conservation Volunteers NZ, which provided much of the labour for the plantings.

The seedlings were planted about 1.5m apart in no distinct pattern because the goal was to create “as close to a natural-looking forest as possible”, Rutledge said.

Straight lines would have been easier from a management point of view but would have persisted for the life of the forest. (My idea of using a spiralling Fibonacci sequence was not taken up.)

Thinning the trees was not planned, Rutledge said.

Kahikatea (white pine) naturally regenerate in dense pole-stands that are sometimes denser than the Mairehau site.

Over time, the trees will thin themselves through competition. At Riccarton Bush, the mature kahikatea are as close as 3m from each other.

The planting site is a low former paddock. It is too wet for housing and used for storm water management.

Kahikatea prefer wet ground, and 95 per cent of plantings in a 2016-17 trial survived.

Mass plantings in 2020 were less successful due to “unusually dry ground conditions,” Rutledge said.

The Mairehau forest will in some respects replace a podocarp forest in Papanui that was entirely felled in early colonial days. The seed was collected from Riccarton Bush and propagated by Steve Bush and colleagues from Trees for Canterbury.

When the trees are established, indigenous trees and shrubs will be planted in the area. It may be opened to the public at some point.

The Mairehau project is part of Matariki Tu Rākau One Billion Trees programme.