The threat to kauri from dieback hasn't gone away but the disease isn't spreading as fast as feared. New management techniques and research into the pathogen attacking the trees are providing hope it can be controlled until a cure is found.
Photo: RNZ / Dan Cook
Five years ago, alarm bells were ringing.
In Auckland's Waitākere Ranges, kauri trees were dying.
It was estimated one in five trees were infected with kauri dieback disease.
Local iwi, Te Kawerau ā Maki, imposed a rāhui in late 2017, followed up a few months later by Auckland Council's decision to close the forest to the public.
But what's happened since then?
Walking tracks have been upgraded and reopened; there are new techniques to monitor and detect the disease remotely; and scientists know much more about how the pathogen that causes the disease works.
But there is still no cure.
Auckland Council kauri dieback biosecurity manager Lisa Tolich describes the Waitākere Ranges as a "touchstone" - a place she feels she needs to return to.
"They're quite awe-inspiring, you walk into one of those immense, mature kauri forest stands and I compare it to a cathedral," she tells The Detail.
"It's just such a sense of awe that you're in the presence of trees that are not just ancient in their own right, we're talking trees that can be upwards of 1000 years or more, but we're also talking trees that whakapapa back to Gondwanaland, their ancestors connect right back to 180 million years ago.
"You're in the presence of trees that have seen many, many things."
Tolich says kauri dieback was first detected in the Waitākere Ranges in 2006, but it was first found in New Zealand on Aotea/Great Barrier Island in 1972.
Kauri dieback disease is caused by a pathogen, called Phytophthora agathidicida.
"This pathogen infects the trees through their sensitive root systems and what it does is it stops the uptake of water and important nutrients up through the trunk and into the canopy of the tree. It essentially starves itself and that's why you see the thinning of the canopy, the loss of all of those leaves, that very skeletal stark structure."
But recent research suggests kauri dieback hasn't spread as far through the Waitākere Ranges as initially feared.
Across the forest, Tolich says a prevalence survey has shown about 10 percent of trees are infected, while 16.5 percent are showing signs of the disease.
"What we did find in the Waitākere Ranges was quite surprising, we found the pathogen was very localised, we found it in a small number of localised sites and they were around the edge of the ranges.
"That heart, that inner sanctum of the Waitākere Ranges we haven't found the pathogen there at all, so that gives us an awful lot of hope that our preventative measures and mechanisms can have an effect. The stable door hasn't closed before the horse has bolted."
Marion Wood is the co-lead of the control, protect, cure research team, which is part of the Ngā Rākau Taketake project looking at ways to save trees from kauri dieback.
She says one key area of research has been around whether it's possible to detect presence of pathogen before a tree actually becomes infected.
"If you think in terms of the pathogen, it wants to infect the tree and it wants to complete its life cycle and part of that life cycle is the development of the disease that we see," she says.
"The earlier we detect the presence of the pathogen and it infecting either directly the kauri tree itself or just the presence in the soil, we want to stop that life cycle, we want to prevent the progression through [the life cycle]."
Ways of intervening to stop the pathogen's life cycle are still being developed.
Wood has hope a cure for kauri dieback disease will be found. She doubts there will be a single silver bullet, and the solution will involve targeting not just the pathogen itself, but the health of the kauri tree and the local environment.
But she warns, like any pathogen, scientists will need to remain vigilant.
"Consider Covid-19 the roles of evolution and the ability to mutate and even increase its ability to infect, it's a real and present threat to search for any single cure.
"We have to be agile, we've got to be flexible and we've got to follow the data. As we come up with a cure, how long will that cure remain viable?"
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