Kauri disease sweeps north

There’s not a lot of good news when it comes to the fungus-like kauri dieback disease, Phytophthora taxon Agathis (PTA), which is killing large numbers of kauri around Auckland and Northland.

By Jay Harkness

Photo: Auckland Council, Nick Waipara

Photo: Auckland Council, Nick Waipara

Little is known about how it is spread and there’s no proven treatment for infected trees. Vandals are tampering with equipment set aside for people to clean their footwear to reduce the chances of spreading the disease.

Trail users are reportedly growing impatient and are demanding to see evidence that track closures in the Waitäkere Ranges will limit the spread of the disease. And government funding for research into the spread of PTA will run out in the middle of next year.

Despite this, Forest & Bird Northland/Auckland Field Officer Nick Beveridge is optimistic that it might still be possible to prevent an ecological disaster.

He says that once a business case has been put together by the Kauri Management Programme – a group made up of the Department of Conservation, iwi, the Ministry for Primary Industries and the Auckland, Northland, Waikato and Bay of Plenty regional councils – new research funding should be granted.

He says that avocado growers successfully treat their trees for similar Phytophthora-type diseases with phosphite (phosphorous acid), and that research at crown research institute Plant & Food Research is showing promising signs that kauri could be treated in a similar way.

Not much is known about how PTA spreads, though there is very good reason to believe that walkers’ footwear is partly to blame.

Members of Forest & Bird’s North Shore and Waitäkere branches voluntarily maintain cleaning stations on Auckland Council reserves in their areas.

But some recent research by the University of Auckland’s Dr Cheryl Krull has identified feral pigs as another likely vector. She found related Phytophthora diseases on the trotters and snouts of pigs in the Waitäkere Ranges. She did not find any signs of PTA specifically but it is strongly suspected that pigs play a role in its spread.

In Australia pigs are known to spread jarrah dieback disease, which survives in a pig’s gut after the animals eat infected roots. The disease establishes itself where their droppings fall. Regardless of whether pigs spread PTA, there are good conservation reasons for culling them, says Nick.

The good news is that, so far, the disease has not spread to kauri south of Auckland, either in the Kaimai or Hünua ranges, on the Coromandel or around Käwhia. However, PTA has been found in Waipoua Forest Park, home to the largest kauri in New Zealand, Täne Mahuta.

The disease is also on possum-free Great Barrier Island (Aotea), from where it seems to have originated in the 1970s. Kauri have been regenerating strongly there since milling stopped in the early part of the 20th century. PTA is also in Northland’s Trounson Kauri Park and in former kauri plantation sites Raetea and Omahuta (near Hokianga Harbour), and Glenburvie (near Whängärei).

It is rife in the Waitäkere Ranges, which lie along Auckland’s western edge. This includes the Forest & Bird/Auckland Councilmanaged Ark in the Park at the northern end of the Waitäkere Ranges.

Nick’s advice to walkers and property owners is simple: “The word on PTA needs to be spread: prevention is the only known cure. People have got to clean everything that could have come in contact with the ground both before going into a kauri forest and as they leave. This includes bikes, tyres, walking poles and, of course, footwear.

“People who have kauri on their land need to be proactive in protecting their trees, and not letting the disease spread from their properties if their trees are infected. This means that visitors and contractors and their equipment need to be checked for any traces of soil.”

Nick says there are many questions about what lies ahead. For instance, will a natural tolerance or genetic resistance develop? And will all kauri be affected in the same way (all kauri known to have been infected so far are dead or dying), regardless of where they are?

Kauri are a keystone species, meaning that ecosystems have evolved to live on and around them. For example, growing kauri create a type of soil (kauri podzol) that only specialised plants can survive in. These species could become extinct if enough kauri die.

And what of the chances of kauri becoming extinct? Could it become the first New Zealand tree to do so? Nick grimly answers that with another question: “How much do New Zealanders value the survival of their native trees?”