Agathis australis

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{{Taxobox | color = lightgreen | name = Agathis australis | status = Conservation status: Secure | image = Kauri Te Matua Ngahere.jpg | image_width = 200px | image_caption = Agathis australis tree 'Te Matua Ngahere' | regnum = Plantae | divisio = Pinophyta | classis = Pinopsida | ordo = Pinales | familia = Araucariaceae | genus = Agathis | species = A. australis | binomial = Agathis australis | binomial_authority = (D.Don) Loudon }}

Agathis australis (Kauri) is a coniferous tree native to the subtropical northern section of North Island in New Zealand and is the biggest species of tree in the country, with trunk diameters that rival Sequoias. They attain heights of 40-50 meters and have smooth bark and small oval leaves.

Young plants grow straight upwards and have the form of a narrow cone with branches going out along the length of the trunk. However, as they gain in height, the lowest branches are shed to prevent epiphytes from climbing. By maturity, the top branches form an imposing crown that stand out over all other native trees, dominating the heights of the forest.

Kauri leaves are 3-7 cm long and 1 cm broad, tough and leathery in texture, with no midrib; they are arranged in opposite pairs or whorls of three on the stem. The seed cones are globose, 5-7 cm diameter, and mature 18-20 months after pollination; the seed cones disintegrate at maturity to release winged seeds, which are then dispersed by the wind. While the reproduction of kauri seed cones takes place between male and female seed cones of the same tree, fertilization of the seeds occurs by pollenation, which may be driven by the same or another tree's pollen.

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Deforestation

The antecedents of the kauri appeared during the Jurassic period (between 190 and 135 million years). Although kauri forests are among the most ancient in the world, their territory decreased considerably due to heavy logging in the past. Kauri today are much less common than in pre-European times.

Although today their use is far more restricted, in the past the size and strength of kauri timber made it a popular wood for construction and ship building, particularly for masts of sailing ships due to its parallel grain and the absence of branches extending for much of its height. Kauri crown and stump wood was much appreciated for its beauty, and was sought after for ornamental wood panelling as well as high-end furniture. Though not as highly prized, the light colour of kauri trunk wood made it also well-suited for more utilitarian furniture construction, as well as for use in the fabrication of cisterns, barrels, bridges construction material, fences, moulds for metal forges, large rollers for the textile industry, railroad ties and braces for mines and tunnels, among many others.

In the late nineteenth and early twentieth centuries kauri gum (semi-fossilised kauri resin) was a valuable commodity, particularly for varnish, and was the focus of a considerable industry at the time.

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Kauri today

The world's remaining Kauri are predominantly found in the northern half of the North Island. The most famous are the Tane Mahuta and Te Matua Ngahere trees in Waipoua Forest in Northland, a 2,500 hectare forest which contains three quarters of New Zealand's remaining kauri. Named after the Māori forest god and 'Father of the Forest' respectively, these two trees have become tourist attractions due to their size.

Tane Mahuta is the biggest existing Kauri which, at present, has a trunk diameter of 4.4 m, a girth of 13.3 m and reaches a height of 51 m. Te Matua Ngahere, also found in Waipoua, is thought to be the oldest existing Kauri tree, estimated to be 2,000 years old. Some of the biggest kauri trees felled in the past were considerably older.

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Wood

Technical specifications

Moisture content of dried wood: 12%
Thickness of wood: 560 kg/m³
Tensile strength: 88 Pascals
Modulus of elasticity: 9.1 Pascals
After felled kauri wood dries to a 12% moisture content, the tangential contraction is 4.1% and the radial contraction is 2.3%

A considerable number of kauri have been found buried in what are today salt marshes, resulting from ancient natural changes such as volcanic eruptions, sea level changes and floods. Such trees have been radiocarbon dated to originating as far back as 50,000 years ago. The bark and the seed cones of the trees often survive together with the trunk, although excavated and in contact with the air, these parts display rapid deterioration.

The quality of the disintered wood varies, and some is in surprisingly good shape, comparable to that of newly-felled kauri, although often lighter in colour. This aspect can be improved by the use of natural dyes, which provide brown dark and greenish tones that heighten the details of the grain. After a drying process, such ancient kauri can still be made use of for furniture and other construction.