(Redirected from Kauri pine)
'''Agathis australis''', commonly known as the 'kauri', is a
coniferous tree found north of 38°S in the northern districts of
New Zealand's
North Island. It is the largest (by volume) but not tallest species of tree in the country, standing up to 50m tall in the emergent layer above the forest's main canopy. 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'.
Though kauri are among the most ancient trees in the world, they have developed a unique niche in the forest. With their novel soil interaction and regeneration pattern they are able to compete with the more recently evolved and faster growing
angiosperms. Because it is such a conspicuous species, forest containing kauri is generally known as 'kauri forest', though kauri need not be the most abundant tree. In the warmer northern climate, kauri forests have a higher
species richness than others found further south.
Description
Foliage on a young tree. Foliage of older trees is usually unreachable.
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, preventing
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 2 m or more.
[1] The kauri has a habit of forming small clumps or patches scattered through mixed forests.
[2]
Kauri
leaves are 3 to 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 to 7 cm diameter, and mature 18 to 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).
Size
''Agathis australis'' can attain heights of 40 to 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). This tree was known as The Great Ghost. Local Thames Historian Alastair Isdale noted this tree was 8.54 metres in diameter, and 26.83 metres in girth. Tragically it was consumed by fire c.1890.
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.
[3]
Growth rate and age
In general over the lifetime of the tree the growth rate tends to increase, reach a maximum, then decline.
[4]
A 1987 study measured mean annual diameter increments ranging from 1.5 to 4.6 mm per year with an overall average of 2.3 mm 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.
[5]
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.
[6]5
Trees can normally live longer than 600 years. Some individuals probably often exceed 1000 years.
5
Root structure and soil interaction
One of the defining aspects of this tree's unique
niche is its relationship with the
soil below. Much like
podocarps, it feeds in the
organic litter near the surface of the soil through fine
root hairs. This layer of the soil is composed of organic matter derived from falling leaves and branches as well as dead trees, and is constantly undergoing
decomposition. On the other hand,
broadleaf trees such as
Māhoe derive a good fraction of their
nutrition in the deeper
mineral layer of the soil. Although its
root system is very shallow, it also has several downwardly directed ''peg roots'' which anchor it firmly in the soil. Such a solid foundation is necessary for a tree the size of a kauri to avoid blowing over, especially during
storms and
cyclones.
The
litter left by kauri is much more
acidic than most trees, and as it decays similarly acidic compounds are liberated. In a process known as
leeching, these acidic molecules pass through the soil layers with the help of
rainfall, and release other nutrients trapped in
clay such as
nitrogen and
phosphorous. This leaves these important nutrients unavailable to other trees, as they are washed down into deeper layers. This process is known as
podsolization, and changes the soil colour to a dull grey. For a single tree, this leaves an area of leeched soil beneath known as a ''cup podsol''. This leaching process is important for kauri's survival as it
competes with other species for space.
[7]
Leaf litter and other decaying parts of a kauri decompose much slower than most other species, however. Besides its acidity, the plant also bears substances such as
waxes and
phenols that are harmful to
microorganisms. This results in a large buildup of litter around the base of a mature tree, in which its own roots feed. These feeding roots also house a
symbiotic fungi known as
mycorrhiza which increase the plant's efficiency in taking up nutrients. In this
mutualistic relationship, the fungus derives its own nutrition from the roots. In its interactions with the soil kauri is thus able to starve its competitors of much needed nutrients and compete with much younger
lineages.
Distribution
Local spatial distribution
In terms of local
topography, kauri is far from randomly dispersed. As mentioned above, kauri relies on depriving its competitors of nutrition in order to survive. However, one important consideration not discussed thus far is the slope of the land. Water on
hills flows downward by the action of
gravity, taking with in nutrients in the soil. This results in a gradient from nutrient poor soil at the top of slopes to nutrient rich soils below. As nutrients leached are replaced by aqueous nitrates and phosphates from above, kauri trees are less able to inhibit the growth of strong competitors such as angiosperms. In contrast, the leeching process is only enhanced on higher elevation. In Waipoua Forest this is reflected in higher abundances of kauri on ridge crests, and greater concentrations of its main competitors, such as
taraire are found at low elevations. This pattern is known as
niche partitioning, and allows more than one species to occupy the same area. Those species which live alongside kauri include
tawari, a montane broadleaf tree which is normally found in higher altitudes, where
nutrient cycling is naturally slow.
Changes over geological time
Kauri is presently found north of 38°S
latitude, its southern limit stretching from
Kawhia Harbour in the west to the eastern
Kaimai Range.
[8]
However, its distribution has changed greatly over
geological time due to the phenomenon of
climate change. This is exemplified in the recent
Holocene epoch by migration southwards following the peak of the last
Ice Age. During this time when frozen
ice sheets covered much of the world's continents, kauri was able to survive only in isolated pockets, its main refuge being in the very far north.
Radiocarbon dating is one technique used by scientists to uncover the history of this tree's distribution, with stump kauri from
peat swamps being used for measurement. The coldest period in recent time occurred very roughly 15-20,000 years ago, and during this time kauri was apparently confined north of Kaitaia, which itself is not far from the northern most point of the North Island,
North Cape. Much like
kumaras grown in New Zealand, kauri requires a mean temperature of 17°C or more for the majority of the year. Kauri's retreat can in fact be used as a
proxy for temperature changes during this period.
It remains unclear whether kauri recolonized the North Island from a single refuge in the far north or from scattered pockets of isolated stands that managed to survive despite climatic conditions. It spread south through
Whangarei, past
Dargaville and as far south as
Waikato, attaining its peak distribution during the years 3000-2000
BP.
8 There is some suggestion it has receded somewhat since then, which may indicate temperatures have declined slightly since this time. During the peak of its movement southwards, it was traveling as fast as 200 metres per year.
8 Regardless of where it originated from, its spread southward seems relatively rapid for a tree that can take a millennium to reach complete maturity. This can be explained by its life history pattern.
Kauri relies on wind as its means of both
pollination and
seed dispersal, whereas many other natives may have their seeds carried large distances by
frugivores (animals which eat
fruit) such as the
kererū, a native pigeon. However, kauri trees rapidly reach a stage at which they can produce seeds, taking only 50 years or so before giving rise to their own offspring. This trait makes them somewhat like a
pioneer species, despite the fact that their long lifespan is characteristic of
k-selected species.
Regeneration and life history
Female cone of ''Agathis australis'', Auckland, New Zealand
Just as the niche of kauri is differentiated through its interactions with the soil, it also has a separate regeneration 'strategy' compared to its broadleaf neighbours. The relationship is very similar to the podocarp-broadleaf forests further south; kauri is much more
light demanding and requires larger gaps to regenerate, whereas broadleaf trees such as
puriri and
kohekohe show far more
shade tolerance. These species can regenerate in areas where lower levels of light reach ground level, for example from a single branch falling off. Kauri trees must therefore remain alive long enough for a large
disturbance to occur, allowing them sufficient light to regenerate. In areas where large amounts of forest are destroyed, such as by logging, kauri seedlings are able to regenerate much easier due not only to increased sunlight, but their stronger resistance to
wind and
frosts. Kauri resides in the emergent layer of the forest, where it is exposed to the effects of the weather, however smaller trees that dominate the main canopy are sheltered both by the emergent trees above and by each other. Left in open areas without protection they are far less capable of regenerating.
Due to this special regeneration niche, kauri trees can live over a thousand years, whereas most other trees experience
senescence long before this time. This extraordinary age is simply a reflection of how long this species must wait in order for there to be a disturbance large enough to favour its regeneration. The nature of this large disturbance also means that kauri trees regenerate ''en mass'', resulting in a ''cohort'' or generation of trees of similar ages forming after each disturbance. Kauri in a given area are hence likely to be of similar age. Due to the nature of their regeneration, the distribution of kauri allows researchers to predict when and where disturbances have occurred, and how large they may have been; the presence of abundant kauri may be an indication that an area is prone to disturbances. Kauri
seedlings still occur in areas with low light, of course, but
mortality rates for such seedlings are much higher, and those that survive
self thinning and grow to sapling stage tend to be found in higher light environments.
During periods with less disturbances kauri tends to lose ground to broadleaf competitors which are more capable of establishing themselves in shaded environments. In the complete absence of disturbance, kauri tends to become more rare as it is excluded by its competitors.
Biomass of kauri tends to decrease during such times, as more biomass becomes concentrated in angiosperm species like
towai. Kauri trees also tend to become more randomly distributed in terms of their age, with each tree dying at a different point in time, and regeneration gaps being rare and sporadic. Over thousands of years these varying regeneration strategies produce a 'tug of war' effect where kauri retreats uphill during periods of calm, then takes over lower areas briefly during mass disturbances. Although such trends are impossible to observe in the lifetime of a human, research into current patterns of distribtuion, behavior of species in experimental conditions, and study of
pollen sediments (see
palynology) have helped shed light on the
life history of kauri.
Ethnobotany
Deforestation
Heavy
logging which began around 1820 and continued for a century has considerably decreased the number of kauri trees in New Zealand.
[9] It has been estimated that prior to European colonisation, the kauri forests of northern New Zealand occupied at least 12,000 square kilometres. By the 1950s this area had decreased to about 1,400 km², 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 (34 shillings/m³).
[10]
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 (47,000 m³), were sold for less than two pounds per tree (two pounds in 1908 equates to around NZD$100 in 2003)
[3].
[11] 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 (8 pence/m³), though the expense of cutting and removing it to the mills was typically great due to the difficult terrain they were located in.
[12]
Uses
Gum sold in Kauri Museum, New Zealand
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 (tree) 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.
Timber
;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.
Conservation and kauri today
''Tāne Mahuta'' ('Lord of the Forest')
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 4 km².
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 80 km² of Waipoua was proclaimed a forest sanctuary after a petition to the Government.
[13]
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 25 km² 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 ft) and a trunk height of 17.68 m (58.0 ft).
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 ft).
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.
References
1. Reed, p.60
2. Reed, p.74
3. Reed, p.89-92
4. Reed p.62
5.
6. Reed p.61-63
7. Site conditions affect seedling distribution below and outside the crown of kauri trees (Agathis australis), , Eric, Verkaik, New Zealand Journal of Ecology, 2007
8. The Late Quaternary History of Kauri (Agathis australis) in New Zealand and Its Climatic Significance, , J., Ogden, Journal of Biogeography, 1992
9. King p.125
10. Reed p.74-75
11. Reed p.267
12. Reed p.79
13. Reed p.268-269
★
The Penguin History of New Zealand, , Michael, King, Penguin Books, ,
★
The Story of the Kauri, , Alfred, Reed, A.H. and A.W. Reed, ,
★
External links
★
Kauri Gum entry from the 1966 Encyclopaedia of
New Zealand
★
New Zealand Department of Conservation page on Kauri
★
Agathis australis description The Gymnosperm Database
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