The Covid-19 virus has had a devastating impact on human life. A mortality rate of 3.4% was estimated by the World Health Organisation at a media briefing on 3 March 2020. By comparison, 1% of those affected are generally killed by the seasonal flu. Thankfully, NZ has been sheltered from the brunt of the impact from a health perspective.
New Zealand’s native Kauri tree is enduring its own life-threatening illness. Like Covid-19, the origins of Kauri Dieback remain uncertain. Though, unlike Covid-19, Kauri trees that contract the soil-borne disease face certain death with a 100% mortality rate. Kauri Dieback is threatening the survival of New Zealand’s largest (by volume) tree species. The iconic coniferous Kauri is among the most ancient in the world and considered a Taonga by Māori.
Thousands of years ago, when the first inhabitants arrived in Aotearoa, Kauri forests were plentiful. Estimates suggest that magnificent Kauri forests covered 1.2 million hectares – spanning Northland to near Kawhia. Not only are the individual trees a cultural icon, they are also critical for the entire native ecosystem – providing shelter and nourishment for other species.
The largest known Kauri standing today is the “god of the forest”, Tāne Mahuta. This giant tree is in Waipoua Forest in Northland and is estimated to be 1250 to 2500 years old. New Zealand’s most famous tree is also considered threatened by this invisible enemy. In 2018, Forest & Bird claimed that “the Kauri could be extinct in our lifetime”.
What is Kauri Dieback?
Kauri Dieback is caused by a microscopic fungus-like organism called Phytophthora agathidicida that spreads in infected soil and can be transported from tree to tree. At one stage, pigs were blamed on the spread of nature’s deadly disease. But now, the focus is squarely on human activity, with over 70% of infected trees in the heavily-impacted Waitakere ranges within 50 metres of public trails.
The pathogen was first discovered on Great Barrier Island in 1972, though, at the time it was wrongly categorised. In 2006, an entomologist by the name of Peter Maddison observed a worrying infection that seemed to be killing Kauri trees in the Waitakere ranges. Debate has raged about how long the pathogen has been on our fair shores, but the speed at which it is spreading suggests it is a relatively new inhabitant. In the five years from 2011, infection rates ballooned from 8% to 19%.
How does it work?
The disease spreads courtesy of dirty footwear, animals, vehicles or equipment. A tiny amount of soil no more than a pinhead is sufficient to transmit the disease.
There are several stages in the development of Kauri Dieback. It’s a bit technical, but here goes…
- Resting spores (Oospores) are introduced into a Kauri area which then germinate to form a sporangia.
- The sporangia produces zoospores which are released with rainfall.
- Zoospores swim in the soil towards the roots of the Kauri and latch onto the outside.
- When they germinate they produce mycelia – which infects the root of the tree and travels through the root system to the base of the Kauri’s trunk.
Once they are roots are infected a Kauri's ability to transport nutrients and water within the tree is compromised, leading to a slow and tragic death by starvation.
Photo credit: AucklandNZ.com
Kauri dieback symptoms may take several years to materialise. In fact, some trees may be infected and show no symptoms at all. However, seedlings typically exhibit symptoms quickly following infection – often within weeks.
A yellowing of the leaves is an initial sign of infection, and trunk lesions can also appear. Root rot can be observed in both fine-feeder and larger structural roots. As the infection takes hold branches can starve and begin to die, before the entire tree loses the battle.
Photo credit: Department of Conservation
What can we do about it?
There is no definitive cure or treatment for Kauri dieback. Our best hope in the immediate term is to contain the spread of the disease by following the appropriate hygiene steps recommended by the Department of Conservation.
- Plan your walk before you leave!
- Ensure footwear is cleaned thoroughly before going for a walk in a Kauri forest.
- Use the cleaning stations provided – participants in the Kauri Dieback programme have installed cleaning stations in Kauri forests – make sure you use them.
- Brush soil off your shoes.
- Inspect your shoes for cleanliness.
- Stay on the track to prevent the spread.
A glimmer of hope
While it may seem like doom and gloom for the majestic Kauri forests, there are signs of hope. A 2019 study proposed that the native Kanuka may hold the key to stopping the spread of Kauri Dieback. The Ngāpuhi iwi has long considered the small evergreen a cleansing plant that performs a vital role in maintaining healthy forests. Now scientists have found that the plant has the capacity to paralyse the spores that spread the deadly disease and can inhibit germination of the pathogen. "If the spores can't move through the soil, they can't infect kauri, which could spell hope for our forests," the authors of the paper said.
Trials are also underway to assess phosphite injections in the trunk of infected trees, a treatment that has been used successfully against Phytophthora cinnamomi in avocado trees. A five-year trial completed in 2017 demonstrated that the injections successfully healed trunk lesions of infected kauri juvenile trees, enabling new bark growth and prolonging the life of the trees. Though, further research is ongoing to understand the impact on mature trees and the performance of phosphate sprays. Phosphite treatment does not kill the pathogen – and is therefore unable to halt the spread to healthy trees in the area.
Kauri Dieback Programme
The Kauri Dieback Programme is a partnership with Biosecurity New Zealand part of MPI, Department of Conservation, Auckland Council, Waikato Regional Council, Northland Regional Council, Bay of Plenty Regional Council, Te Roroa (tangata whenua for Waipoua Forest), and Tangata Whenua Roopu.
There is a significant amount of work being undertaken by the Kauri Dieback Recreation Project team to protect our endangered trees including the upgrading and re-routing of tracks, closure of some tracks or modifications to recreational use, the installation of hygiene stations, and signage to educate users and deliver behavioural change.
Where is Kauri Dieback?
The following map shows the locations where the infection by Phytophthora agathidicida has been detected.
What if I want to go walking?
You can find a list of the track closures due to the spread of Kauri Dieback on the Department of Conservation website. Please follow the guidance and protect our mighty trees!
1% of our sales of Lone Kauri natural deodorants go towards Kauri Tree conservation. Help us protect their fragile ecosystem.