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Kauri

Kauri is the largest and most renowned of all the native timber trees.

Kauri in its heyday was a very versatile timber, of which large planks could be obtained, in an unblemished state as the tree has no branches for much of its trunk height, and unlike totara, was solid throughout the trunk.Post WW2, the timber was reserved for boat building, due to diminishing supplies.

Recovered kauri from swamps makes a most interesting turnery timber, and recycled kauri from old buildings is excellent for carving, and can hold a fine edge.

Second-growth and plantation timbers are suitable for all interior purposes where a moderately dense softwood species is suitable, and makes an excellent furniture timber.

Kauri can also be easily peeled or sliced for veneering purposes.

Description

kauri_90

Kauri grows naturally only in the upper North Island, north of a line from Kawhia in the west and Tauranga in the east. Remaining mature trees can be up to 5 metres in diameter.

The largest kauri tree (based on volume, some kauri went up to 7 m dbh) recorded, Kairaru, had a girth of 20 metres, and a diameter of over 6 metres.

Most of the forest giants were removed between 1840 and 1920, those that remain are located in the Coromandel, Great Barrier and western Northland.

Kauri forest, is however, regenerating throughout the region into second-growth forests, and there is quite a volume of swamp kauri recovered from farmland in Northland.

With most supplies of mature Kauri suitable for timber now exhausted or in reserves, there is wide interest in establishing and managing planted Kauri for market and non-market benefits Second-growth forest may exceed 60,000ha.

Additionally, younger plantation timber is able to be grown in regions south of the natural regeneration zones of the upper North Island.

Kauri timber is a light honey colour, with a distinctive silvery speckled lustre. It looks similar to macrocarpa sapwood in lustre and colouring, but does not have growth bands.

More information – Kauri (.pdf)

Botanical name: Agathis australis

Other common names: Kauri

Strength: Moderately strong.

Durability: Kauri is non-durable in-ground but suitable for exterior use as long as it is properly protected from weather.

Finishes: Not applicable.

Working properties: Easy to work.

Appearance: Kauri timber is a light honey colour, with a distinctive silvery speckled lustre. It looks similar to macrocarpa sapwood in lustre and colouring, but does not have growth bands.

Properties

The timber of mature kauri from old-growth forests (400 to 1000 yrs old) is easy to dry, easy to work, stable, moderately strong and durable.

Mature kauri has a density of 560kg/m³, a tangential shrinkage from green to 12% moisture content of 4.1% percent, and a radial shrinkage of 2.3%. This kauri is very stable once dry. Mature kauri has a modulus of rupture of 88 MPa and a modulus of elasticity of 13.0 GPa.

Kauri’s reputation as an excellent general-purpose timber species is related to the heartwood that constituted a significant proportion of the often-large diameter (>2 m) stems of natural old-growth stands.

Studies undertaken in 1983 on a 120-150 year old regenerated kauri stand, and in 2002 on 68 year old plantation kauri, indicate that the plantation kauri timber has similar properties to 120-150 year old regenerating stands, and similar stiffness and stability properties, although hardness is likely to be significantly diminished.

The timber properties of second-growth regenerated and plantation kauri (those 80-100 yrs old) have been found to be little different to old growth timbers for strength, dimensional stability and density of sapwood.

However, these second-growth trees have very little heartwood timber. Kauri is non-durable in-ground but suitable for exterior use as long as it is properly protected from weather. Comparison of density, stiffness, and shrinkage for old-growth, regenerated second-growth, and plantation-grown kauri.

 Basic density (kg/m3)Stiffness (MoE)
(GPa)
Shrinkage
Radial
(%)Tangential
Old-growth56013.02.34.1
Second-growth47210.82.63.9
Plantation45113.62.94.1

Further information:

Steward, G. and McKinley, R. 2005. Plantation-Grown New Zealand Kauri: A Preliminary Study Of Wood Properties. New Zealand Journal of Forestry Science 35(1): 35–49 (2005).

Availability
Limited supplies may be available. Refer to the New Zealand Farm Forestry Association website for information regarding local timber suppliers.