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Kauri forest

by  Joanna Orwin

Giant kauri trees were considered by Māori to be the kings of New Zealand’s forest. The straight-grained wood was prized by Europeans as spars for sailing ships and became popular in construction. With logging, tracts of native forest soon dwindled. Today the patches that remain are being carefully protected, and the forest is being restored.


How and where kauri grows

One of the largest and longest-living trees in the world, New Zealand kauri (Agathis australis) belongs to the ancient conifer family, Araucariaceae. Agathis is one of three still-existing southern hemisphere genera of Araucariaceae, and is thought to have evolved in the Australia–New Zealand region. New Zealand kauri appeared about 20 million years ago. Agathis contains about 20 species found along the western Pacific and into New Guinea, the Philippines, Indonesia and Malaysia. The most southern-growing species, New Zealand kauri, is restricted to the sub-tropical forests in areas north of latitude 38° S (in Auckland, Northland and the Coromandel Peninsula), where it grows from sea level to 600 metres.

Bark, leaves and cones

The trunk of the full-grown kauri has greyish bark with a pattern like hammer marks, caused by the bark flaking off. Kauri gum (sometimes called New Zealand amber) oozes from the bark of mature trees. The tree’s oblong leaves are flat and leathery; bronze when young but turning bright green as they mature.

Kauri trees bear both male and female cones. Male cones are finger-shaped and fall once they have released their pollen in spring. Female cones are round and turn from green to brownish red as they mature. They ripen after three years of growth and release seeds that are dispersed by the wind.

Gum bandage

Kauri gum or resin oozes from the bark, leaves and cones of all kauri trees, and large deposits form where the branches fork. It is how the kauri protects itself from injury and decay. The gum hardens to seal any damaged surfaces, slowing the onset of rot and warding off insect attack.

Growth

Like most conifers, young kauri have a narrow pyramid shape. As the trees reach the forest canopy, which takes 50 years or more, they shed their lower branches to become clean-stemmed ‘rickers’ – named after the ships’ spars for which they were once logged.

Mature kauri develop massive column-like trunks, with spreading crowns supported by whorls of large branches. These huge structures are balanced by spreading lateral roots anchored with peg roots that can extend 5 metres into the ground. The feeding roots form a fine surface mat within the litter mound that surrounds each tree.

Size

Kauri’s final size depends on site and conditions, but heights average 30–40 metres and trunks can reach several metres in diameter. By 600–700 years of age, kauri reaches an average diameter of over 1 metre. Kauri can survive for 1,000 years or more (with an average diameter of 2 metres), but trees older than 1,700 years (average diameters over 3 metres) are now rare. The ages of the largest survivors like Tāne Mahuta (‘the god of the forest’, diameter over 4 metres) are not accurately known, but have been estimated at 1,500–2,000 years. Even bigger trees were known in the past, some with diameters of more than 7 metres.

Distribution

Before people settled in New Zealand, forest containing kauri covered much of the Coromandel Peninsula and northern areas. Today, the remaining 7,455 hectares of mature kauri forest is scattered in remnant patches. Fossil evidence shows that it once grew as far south as Invercargill. Over the last few million years, kauri retreated to its present limits as a result of geological-scale disturbances such as sea-level changes, mountain-building, volcanic eruptions and glaciations, and the associated loss of suitable soils.


Kauri forest ecology

Many forest types contain kauri. These have different features, reflecting soils, terrain, and temperature. Kauri forest is structurally complex, often with 20 different tree species per hectare. In mature stands, kauri trees emerge above a canopy of smaller conifers and broadleaved trees. Up to nine other conifers, including rimu (Dacrydium cupressinum), mountain tōtara (Podocarpus hallii), miro (Prumnopitys ferruginea), and further south, hard beech (Nothofagus truncata) can grow alongside kauri.

Kauri forest is similar to other sub-tropical forests. Some trees have buttressed trunks, and many are festooned with lianes (woody twining plants) and perching epiphytic plants. There are tree ferns, nīkau palms and orchids. Kauri forest contains the sole New Zealand representatives of some tropical Pacific families, such as pūriri (Vitex lucens), taraire (Beilschmiedia tarairi) and kohekohe (Dysoxylum spectabile).

The lower, open tiers of the forest contain small trees and shrubs, many of which are found only in kauri forest. Ground cover is predominantly kauri grass (a native lily, Astelia trinerva), a sedge-like plant (Gahnia xanthocarpa) and the liane kiekie (Freycinetia banksii).

Gumlands

In the far north, extensive areas of podzolised soils can be accompanied by compacted layers that develop in poorly drained sub-soil. These areas now support only stunted scrub species like mānuka and kānuka. Known as ‘gumlands’ because of the large deposits of fossil kauri gum once found in them, they are a legacy of former kauri forest.

Podzolised kauri soils

Wherever kauri grow, their mark is left in the soil. Kauri forest flourishes on a wide range of podzolised soils – poorly drained, strongly weathered, acidic clay soils, out of which heavy rainfall has leached most of the nutrients needed for plant growth. The presence of kauri intensifies this process so that long after the forest has disappeared, nutrient-poor areas in the soil show where individual trees once grew.

Competition with other trees

Adaptation to nutrient-poor soils is one way that slow-growing conifers like kauri can compete successfully with faster-growing broadleaved trees. Kauri forest tends to occupy the poorest soils, with broadleaf forest on more fertile soils. Because kauri can tolerate a range of soil moisture conditions they will grow on sites as varied as drought-prone ridge tops, podzolised sand dunes, and waterlogged rolling terrain (such as Waipoua Forest).

Kauri contribute to the low fertility of podzolised soils by producing a deep layer of litter that is slow to decay because it includes woody components such as bark, branchlets and cones, as well as kauri gum. Leaves, normally a large component of litter, are retained on the tree for up to 15 years.

This litter eventually develops into a highly acidic humus that is slow to release nutrients. It is another strategy by which kauri edge out competing broadleaf species.

Nitrogen recycling

The nutrients locked up in kauri litter include up to four times the nitrogen stored in the litter of most other forest types. Some of this is contributed by nitrogen-fixing bacteria that live in the surface layers of kauri litter. All this stored nitrogen is relatively inaccessible to plants – including kauri.

How then can kauri achieve their massive size and grow vigorously for hundreds of years? Although kauri do show signs of nitrogen deficiency (and respond to nitrogen fertilisers), they are highly efficient nitrogen users. With the help of specialist fungi (called mycorrhizas), kauri forest produces nearly twice the amount of wood, bark and cones for a given amount of nitrogen than that achieved by most other forest types. Kauri is the ultimate recycler.


Using kauri

Māori and kauri

For Māori, the tallest trees in the forest traditionally had chiefly status. In the north of New Zealand, kauri held the highest rank. This is reflected in sayings such as, ‘kua hinga te kauri o te wao nui a Tāne’ (the kauri has fallen in the sacred forest of Tāne) – repeated whenever a great person dies.

Legs like tree trunks

Kauri features in a northern version of the creation story of Ranginui, the sky father, and Papatūānuku, the earth mother. At the beginning of time Rangi and Papa clung together, trapping their children in the darkness between them. The strongest child, Tāne Mahuta (the god of the forest), pressed his shoulders against his mother and pushed upwards with his powerful legs, separating his parents and allowing light to enter and bring life to the world. Some northern Māori tribes say that his legs were the trunks of giant kauri trees.

Although revered, kauri was considered less useful than other trees such as tōtara and miro, which not only provided superior timber for buildings and carving, but produced berries that attracted birds, an important source of food. Kauri gum was valued more highly than the wood: it could be used as a fire starter, and for medicinal purposes. The soot from burnt gum was a tattooing pigment. The straight-grained, buoyant timber was, however, ideal for canoes.

The timber trade

The qualities of kauri timber impressed the first Europeans who visited northern New Zealand from the late 1700s. The elasticity and length of the trunks made them ideal for ships’ spars. By the mid-1820s, timber merchants, pit-sawyers, and shipbuilders were setting up shore stations throughout the northern region. Māori traded kauri spars and provisions for European goods, and later for muskets.

The timber and gum industries

When European settlement picked up pace after 1840, there was also a growing need for sawn timber for construction. By the mid-1860s, steam-driven sawmills were springing up along the many harbours and waterways of the kauri region. From the 1870s to the 1910s, sawmilling was the biggest employer in the Auckland province. Many sea-going ships and coastal scows, built from kauri, served the expanding export and domestic timber industry. During this period kauri gum, prized for use in varnish and linoleum, was dug from Northland’s swamps and exported in large quantities.

Logging

Extracting kauri logs from remote and rugged bush country was physically demanding and dangerous work. The bushmen cut felled trees into manageable lengths, then used levers, timber jacks, and blocks and tackle to roll them into creek beds. Here the logs accumulated until floods could float them downriver into tidal inlets and harbours for collection by scows and ships.

Kauri overseas

In the mid-19th century kauri timber, roofing shingles and prefabricated houses were shipped to Sydney and then to San Francisco, the major port on the American west coast. Kauri helped build these cities, and after the devastating San Francisco earthquake and fire of 1906, it was used in rebuilding.

By the 1850s, skilled bushmen were using timber felled on site to build dams to augment natural floods. An estimated 3,000 dams were built, mostly in the Waitākere Ranges (Auckland) and the Hokianga, and on the Coromandel Peninsula. Thousands of logs could be sent down the waterways after the synchronised triggering of dams. Although very efficient, such drives may have destroyed an estimated 30–40% of the logs felled. In later years, steam haulers and tramways replaced the use of dams.

Disappearing forest

In just over 100 years, logging and burning transformed the northern landscape from forest to farmland. By the early 1900s, most kauri forest had been logged. Although there was growing concern for the survival of remaining native forest, the high value of kauri timber meant that the forest was still exploited. A final push to extract the last of the kauri swept through the north in the 1920s and 1930s, reducing the forest to the few patches that survive today.


Protecting kauri

Today, kauri is showing its ability to benefit from major disturbances. Saplings are emerging through scrubland where farming was abandoned on kauri-depleted soils. The amount of regenerating secondary forest and scrubland containing kauri (estimated at 60,000 hectares) far exceeds that of the remnant mature forest. The places where kauri grow are being protected and restored by conservation authorities and local communities.

Protection and management

Concerns about the unsupportable rate of cutting kauri and other native forest emerged as early as 1863, and many of the remaining patches of forest were classed as reserves by the early 1900s. Despite this, government policy for managing the remaining forest did not gain momentum until after the First World War.

The last kauri

Artist Rei Hamon was once manager of the Thames Sawmilling Company and had the job of supervising the felling of a large kauri above Tapu in 1961. He recalls, ‘When that tree fell, it had been standing there for maybe a thousand years…I went back later to where it had been standing, and there were birds fluttering around there, kaka and kereru, that had nested in that tree for generations. That was the finish. I handed in my resignation. I vowed never to fell another healthy tree.’ 1

Although foresters continued to manage regenerating stands for timber, public opinion was turning against further logging. In the early 1950s, Professor Roy McGregor led a successful campaign to protect the old kauri stands of Waipoua Forest in Northland. Battles between conservationists and foresters continued until the 1980s. Growing recognition of the intrinsic value of native forest finally led to the end of all logging of live kauri trees in state forests by 1985. The ongoing demand for the timber meant that privately owned resources were targeted until quite recently, when compliance costs outweighed demand.

Threats to survival

Protection from logging has not ensured the preservation of kauri forest. Introduced animal pests threaten native plants and animals. Possums in particular compete for food with rare birds like kōkako and predate their nests, and they strip native trees. But the Department of Conservation faces ongoing public resistance to using 1080 (sodium monofluoroacetate) to control possums in large areas of remote forest.

The spread of weeds into degraded kauri forest is equally damaging. The forest is particularly vulnerable because of the warm, wet northern climate. More than 100 weed species now threaten native habitats in Northland alone.

Kauri dieback disease

A major threat to the kauri is kauri dieback, a disease caused by a fungus-like water mould Phytophthora taxon Agathis. First observed on Great Barrier Island in the 1970s, the disease was formally identified in 2008. The spores of the water mould first attack the kauri roots and then damage the tissues that carry nutrients. The leaves begin to yellow and fall, the canopy thins, branches die, lesions bleed resin at the base of the tree and eventually the tree dies. There is as yet no known cure. The disease has been found in many areas including the Waitākere Ranges, Trounson Kauri Park and Waipoua Forest. In 2012 it was still not detected in the Hūnua Ranges and the Coromandel. Since the spores are carried in soil, the best prevention is to ensure that shoes and any equipment in contact with the soil are clean before visiting a kauri forest. A charter was set up among a number of public agencies to establish a kauri dieback programme and manage the spread of the disease.

Restoration

Efforts to restore kauri forest now range from official operations to volunteer work. As well as pest and weed control, the Department of Conservation intensively manages a ‘mainland island’ at Trounson Kauri Park, near Waipoua. Community groups tackle weeds and pests, plant and raise native species, and assist the department with associated species recovery. Private trusts like the Waipoua Forest Trust (a joint partnership between the Forest Restoration Trust and Te Roroa, the Māori guardians of Waipoua), Kauri 2000 (a Coromandel initiative), and the Puketi Forest Trust are establishing thousands of kauri seedlings on suitable sites.

Future growth

Reliable information on growing kauri is readily available. Well-managed kauri stands have good growth rates, and the renewed production of kauri timber on private land has considerable potential. Tane’s Tree Trust, set up in 2001, co-ordinates research and information-sharing, and lobbies the government to promote native timber plantations on private land.

Whether protected for its intrinsic value or managed for its timber, it seems certain that kauri forest will one day reclaim more of the northern landscape.

Footnotes
    • Quoted in Joanna Orwin, Kauri: witness to a nation’s history. Auckland: New Holland, 2004, p. 174. › Back

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How to cite this page: Joanna Orwin, 'Kauri forest', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/kauri-forest/print (accessed 20 October 2017)

Story by Joanna Orwin, published 24 Sep 2007