Agathis australis

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Agathis australis

Agathis australis tree 'Te Matua Ngahere'

Conservation status

Conservation Dependent

Scientific classification

Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Araucariaceae
Genus:	Agathis
Species:	A. australis

Binomial name

Agathis australis
(D.Don) Loudon

Agathis australis, known as the kauri, is a coniferous tree native to the northern districts of the North Island of New Zealand and is the biggest but not tallest species of tree in the country. The tree has smooth bark and small oval leaves. Other common names to distinguish A. australis from other members of the genus are southern kauri and New Zealand kauri.

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.

The flaking bark of the kauri tree defends it from parasitic plants, and accumulates around the base of the trunk. On large trees it may pile up to a height of 2m or more.(Reed 1953, p. 60) The kauri has a habit of forming small clumps or patches scattered through mixed forests. (Reed 1953, p. 74)

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, fertilisation of the seeds occurs by pollination, which may be driven by the same or another tree's pollen.

Kauri forests are among the most ancient in the world. The antecedents of the kauri appeared during the Jurassic period (between 190 and 135 million years).

Agathis australis can attain heights of 40 - 50 metres and trunk diameters big enough to rival Californian Sequoias at over 5 meters. The largest kauris do not attain as much height or girth at ground level but contain more timber in their cylindrical trunks than a comparable Sequoia with its tapering stem.

The largest specimen of which there is any known record grew on the mountains at the head of the Tararu Creek that falls into the Hauraki Gulf just north of the mouth of the Waihou River (Thames). It was said to be 8.5 metres in diameter, though its height is not mentioned and there are no officially recorded measurements.

A kauri tree at Mill Creek, Mercury Bay was measured in the early 1840s to be 22 metres in circumference and 24 metres to the first branches. It is thought that this tree was felled around 1870. (Reed 1953, p. 89-92)

In general over the lifetime of the tree the growth rate tends to increase, reach a maximum, then decline. (Reed 1953, p. 62)

A 1987 study measured mean annual diameter increments ranging from 0.15 to 0.46cm per year with an overall average of 0.23cm per year. This is equivalent to 8.7 annual rings per centimetre of core, said to be half the commonly quoted figure for growth rate. The same study concluded only a weak relationship between age and diameter. Individuals in the same 10 cm diameter class may vary in age by 300 years, and the largest individual on any particular site is often not the oldest. (Ahmed, Ogden 1987)

Experts agree that because of the variation in growth rate it is not possible to accurately assess the age of a standing tree from its diameter alone. (Reed 1953, p. 61-63), (Ahmed & Ogden 1987)

Trees can normally live longer than 600 years. Some individuals probably often exceed 1000 years, but there is no conclusive evidence that trees can exceed 2000 years in age. (Ahmed & Ogden 1987)

Heavy logging which began around 1820 and continued for a century (King 2003, p. 125) has considerably decreased the number of kauri trees in New Zealand. It has been estimated that prior to European colonisation, the kauri forests of northern New Zealand occupied at least 1.2 million hectares. By the 1950s this area had decreased to about 140,000 hectares, comprising some 47 forests which were depleted of their best kauri. By 1900, less than 10% of the original kauri had survived. It is estimated that today, there is 4% of uncut forest left in small pockets. [1]

Estimates are that around half of the timber had been accidentally or wilfully burnt. More than half of the remainder had been exported to Australia, Britain, and other countries, while the balance was used locally for building houses and ships.

Much of the timber was sold for a return sufficient only to cover wages and expenses, plus reasonable interest on the capital employed in the industry. From 1871 to 1895 the receipts indicate a rate of about 8 shillings (around NZD$20 in 2003)[2] per hundred superficial feet. (Reed 1953, p. 74-75)

The Government continued to sell large areas of kauri forests to sawmillers who, under no restrictions, took the most effective and economical steps to secure the timber, resulting in much waste and destruction. At one sale in 1908 more than five thousand standing kauris, totalling about twenty million superficial feet, were sold for less than two pounds per tree (two pounds in 1908 equates to around NZD$100 in 2003)[3].(Reed 1953, p. 267) It is said that in 1890 the royalty on standing timber fell in some cases to as low as twopence (NZD$0.45 in 2003)[4] per hundred [superficial] feet, though the expense of cutting and removing it to the mills was typically great due to the difficult terrain they were located in.(Reed 1953, p. 79)

In 1921 a philanthropic Cornishman named James Trounson sold to the Government for 40 thousand pounds, a large area adjacent to a few acres of crown land and said to contain at least four thousand kauris. From time to time Trounson had added further areas by way of gift, until what is known as Trounson Park comprised a total of 400 hectares.

The importance of Waipoua Forest in relation to the kauri was that it remained the only kauri forest retaining its former virgin condition, and that it was extensive enough to give reasonable promise of permanent survival. On 2 July 1952 an area of over 8,000 hectares of Waipoua was proclaimed a forest sanctuary after a petition to the Government. (Reed 1953, p. 268-269)

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.

The small remaining pockets of kauri forest in New Zealand have survived in areas that were not subjected to burning by Māori settlers and were too inaccessible to European loggers. The largest area of mature kauri forest is Waipoua Forest in Northland. Mature and regenerating kauri can also be found in other National and Regional Parks such as Puketi and Omahuta Forests in Northland, the Waitakere Ranges near Auckland, and Coromandel Forest Park on the Coromandel Peninsula.

The most famous specimens are Tāne Mahuta and Te Matua Ngahere in Waipoua Forest, a 2,500 hectare forest which contains three quarters of New Zealand's remaining kauri. These two trees have become tourist attractions due to their size. Tane Mahuta, named after the Māori forest god, is the biggest existing kauri with a girth of 13.77 m (45.2 feet) and a trunk height of 17.68 m (58.0 feet).

Te Matua Ngahere, which means 'Father of the Forest', is smaller but stouter than Tane Mahuta, with a girth (circumference) of 16.41 m (53.8 feet).

Kauri is common as a specimen tree in parks and gardens throughout New Zealand, prized for the distinctive look of young trees, its low maintenance once established (though seedlings are frost tender), and small footprint.

Technical specifications

Moisture content of dried wood: 12%
Density of wood: 560 kg/m³
Tensile strength: 88 MPa
Modulus of elasticity: 9.1 GPa
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 or older. The bark and the seed cones of the trees often survive together with the trunk, although when excavated and in contact with the air, these parts display rapid deterioration.

The quality of the disinterred 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.