Kauri Dieback in New Zealand

Sep 26, 2011
Bridget Murray

Trigene located at entry of Hunua track - B Murray

Kauri (Agathis australis) is endemic to New Zealand and after surviving extensive milling they face a new threat known as Kauri Dieback.

There are two main types of forests in New Zealand; Beech Forest and Podocarp/Broadleaf forests. However the kauri tree is an imposing and dominant feature in some forests and as a result they are often referred to as kauri forests. Waipoua Forest is a superb example of the kauri forest and is home to New Zealand’s largest known kauri tree, Tane Mahuta, Maori for 'Lord of the forest.' In the late 1800's to early 1900's kauri trees were extensively milled after European settlement as the tall, straight trees made ideal ships masts. Since then there has been no real threat to their continued survival however a new threat known as kauri dieback has emerged affecting kauri trees of all ages and sizes.

The Kauri Tree: Description and Distribution

Genus: Araucariaceae – ‘named for the place where Araucaria grows in Central Chile' (Eagle, 2006).
Family: Agathis – meaning a ‘ball of thread, referring to the appearance of the cone: from the Greek, agathis’ (Eagle, 2006).
Species: australis – meaning ‘Southern; from the Latin, australis, southern’ (Eagle, 2006).

While Agathis species can be found in other countries including Fiji, New Caledonia, and Australia, Agathis australis is endemic to New Zealand and its distribution of kauri is restricted to N. North of 38oS (Eagle, 2006). They favour infertile areas in lowland forest areas.

Kauri can grow to more than 50m in height with the first branches appearing at 25m and the trunk typically 7m in diameter. The bark is an ash grey colour that falls in sizeable flakes that gather at the base of the trunk.

The varying characteristics of leaves are often used to isolate and identify trees but their general appearance can often differ in young and mature trees. Kauri leaves are located opposite and brown in young trees and alternate and green in mature trees. They are spear shaped, coriaceous (tough leathery exterior) and parallel veined.

The seeds/cones of kauri are monoecious (both male and female cones on every tree). They are compressed and ripen over two years and dispersal occurs when the scales open to release the seed or the cone falls and breaks open.

What is Dieback and how is it Affecting Kauri?

Phytophthora taxon Agathis (PTA) is a pathogen (disease causing organism) that resembles a microscopic fungus. It belongs to a distinct group known as water moulds falling under Kingdom Chromista. Its presence has been noted on Great Barrier Island for the past 30 years and has since spread to the mainland affecting kauri in Auckland and Northland (Forest and Bird).

Research into PTA is still in its infancy and to date the origin and time of arrival into New Zealand is unknown but it is believed to be an exotic species. So far there is no known treatment for PTA however there are other PT species that are known to be sensitive to both low or high temperatures and UV treatments. Further research may show that these treatments may have a similar affect on PTA.

The Impact of PTA

Depending on which source you read kauri trees have been estimated to live up to 2000 - 4000 years (Dawson & Lucas, 2000 & Eagle, 2006). PTA affects only kauri trees at every stage of their lifecycle including mature species that have existed for hundreds, possibly thousands of years. Symptoms of affected trees include:

Leaves turn yellow.
Defoliation.
Canopy thinning.
Dead branches.
Lesions that bleed resin including the major roots.
Both young and mature kauri trees are susceptible to PTA alike to the point of death.

How You Can Help Prevent the Spread of PTA

As there are no spores the movement of PTA is not airborne. It is therefore believed to travel through soil and to a limited degree water movement. Movement through contact with humans and animals are also of concern. Preventative measures to avoid further spread of the disease causing pathogen can include the following:

Stay on the tracks and keep your distance from the roots. If you are walking with your dog keep them on a leash to prevent them from leaving the tracks and away from the roots.
When you enter and leave an area with kauri trees make sure you scrub soil or mud off footwear especially if you are entering another area with kauri trees. Or a disinfectant such as Trigene in the interim.

To report any suspected sightings or to find out more contact the Kauri Dieback Management Team on 0800 NZ KAURI.

Kauri trees are endemic to New Zealand and with the likes of Tane Mahuta they have been an inspiration to many. This is not the first time kauri trees have been threatened but in this case everyone can do their part to help limit the spread of this disease until further research, and long term management tools can be found for the eradication of the disease.