The pathogen that causes kauri dieback disease isn't believed to be in the heart of Auckland's Waitākere Ranges, a new council survey has found.
After surveying 2140 trees in 2021, Auckland Council found the soil-borne pathogen - Phytophthora agathidicida - in localised areas within the periphery of the regional park, which is home to one of the largest kauri forests in the country.
The majority (80.7%) of trees surveyed were either healthy (53.2%) or 'ill-thrift' (slightly unwell, 27.5%).
It also found more trees had kauri dieback symptoms (16.5%) than had the pathogen in their soil (10%).
The survey also said the trees were four times more likely to have kauri dieback symptoms if the pathogen was found in their soil.
"Encouragingly" kauri seedlings and saplings were recorded at 55% of the sites surveyed and were found in areas where the pathogen was detected. It is considered a good omen or tohu of regeneration.
The survey further discovered trees with kauri dieback symptoms were bigger, near historic timber sites, the coast, and closest to uphill tracks.
There was a similar finding for the pathogen's prevalence. It was more common near the coast and historic timber sites too, but its prevalence reduced at higher elevations and sometimes due to the distance between neighbouring trees.
Auckland Council said the survey was a remarkable feat in itself. Along with the 2140 trees surveyed, 761 had their soil sampled and 4450 field team hours went into it.
Unlike previous surveys in 2011 and 2016, the council said the 2021 survey moved beyond simply mapping the pathogen's presence and the extent of the disease in visible areas of decline.
New remote sensing technology and epidemiological modelling had enabled a better understanding of kauri population health, it said.
The council added the 2021 survey will allow it and iwi Te Kawerau ā Maki to monitor the impacts of its "management interventions" and the health of the kauri population over time.
Survey's findings 'means there's hope'
Auckland Council's kauri dieback manager Lisa Tolich told 1News the survey's findings were "quite heartening" as the pathogen was "incredibly localised".
"It basically means there's hope. The horse has not bolted," she said.
"That part of the ranges is entirely defendable and there is a lot we can still do in that space with the population of healthy kauri."
Tolich said the survey supported the council's "precautionary approach" to managing the disease in the ranges, which included closing large expanses of forested areas in May 2018.
The closures weren't popular with some, with two men fined for repeatedly entering closed or prohibited areas of the Waitākere Ranges.
However, the closures have allowed the council to upgrade 48km of tracks, allowing 30 to reopen. Another track is set to reopen by the end of this month. Nine more tracks currently under construction will reopen in the next financial year.
Chairman of the council's Environment and Climate Change Committee Richard Hills said the survey's findings showed it was heading in a positive direction in terms of its kauri dieback management.
He said the pathogen was slower moving than first believed and large stands of kauri remain unaffected.
There is hope for the next generation of kauri, he reflected.
However, both Hills and the survey report warned vigilance is still needed to slow or stop the spread of the disease within and beyond the ranges.
What is kauri dieback?
The pathogen that causes kauri dieback disease lives in the soil and infects kauri roots.
It damages the tissues that carry nutrients and water within the tree, effectively starving it to death.
More advanced stages of kauri dieback disease can be seen above the ground, with trees losing leaves and developing bleeding lesions on the roots and lower trunk.
There is no known cure or treatment for the disease and nearly all infected kauri die.
Dirty footwear, animals, equipment and vehicles can spread the pathogen, that's why people are asked to clean and disinfect their footwear when they're around native trees. It's also why people are asked to stick to the tracks. Just a pinhead of soil can spread the disease.