Death Sentence for Tane Mahuta

Our beloved kauri forests need more help if they are to beat a killer disease. By Mark Bellingham.

Kauri dieback disease could kill off plans for a Kauri National Park in Northland by eliminating kauri from northern forests. Imagine Waipoua Forest with no Täne Mahuta or Te Matua Ngahere, Puketi Forest with no Te Tangi o te Tüï and no kauri in the WaitäkereRanges Cascades Kauri Park.

Kauri are icons of Aotearoa, and the majesty of kauri is deeply engrained in Mäori and Päkehä culture and history. On average, kauri grow to 30-40 metres and can live for more than 1000 years, with trunk diameters of several metres.

The largest kauri recorded was Kairaru of Tutamoe, with a diameter of 6.4 metres and a height of 65 metres. The largest kauri alive, Täne Mahuta, has a diameter of 4.6 metres, is 52 metres tall and is 1200-2000 years old.

A pathogen known as Phytophthora taxon Agathis (PTA) could change everything. The pathogen and the disease may have been here for some time, as significant dieback of kauri trees was reported on Great Barrier Island in the 1970s. It wasn’t identified as a disease specific to New Zealand kauri until former Forest & Bird President Dr Peter Maddison and local residents reported it on the Maungaroa Ridge Track near Piha in 2006.

These observations were investigated by the late Dr Ross Beever (Landcare Research) and Dr Nick Waipara (now with Auckland Council biosecurity), who confirmed that something new was killing our kauri. In April 2008 it was identified as a new species
PTA symptoms include yellowing of foliage, canopy thinning, dead branches and tree death.

Trees can also develop lesions that bleed resin, often at the bottom of the tree trunk, and the disease has been called collar rot. It kills kauri of all ages and sizes. The disease has been found in the kauri forests of Northland, including Waipoua, Trounson Kauri Park
and Puketi, and in Auckland, including the Waitäkere Ranges, where Auckland Council biosecurity has it under observation at Cascade Kauri, Karekare, Anawhata and
Huia. So far the Hünua Ranges are PTA-free.

Recent investigation has found PTA at the site of the old New Zealand Forest Service’s kauri management nurseries, suggesting that the disease may have come in with foreign Agathis species imported by the Forest Service to “improve” our kauri in the 1960s and 70s. This may explain why its closest known relative is a chestnut pathogen from Korea (Phytophthora katsurae).

It is believed that PTA is an exotic pathogen, possibly from the tropics. However,
nothing at all is known about this particular species overseas.

Kauri damage has only recently been discovered but the disease may have been in New Zealand for many years, as symptoms may take years to become apparent. PTA is spread by soil and soil-water movement, plantto- plant transmission through underground root-to-root contact, and human and animal vectors, such as other soil.

PTA does not produce airborne spores. Its motile (swimming) waterborne spores can move through soil waterfilms, streams, ponds and lakes but these spores have not been detected in stream samples from the heavily infested areas of the Waitäkere Ranges. And they don’t
survive very long.

Soil-borne spores can survive for longer periods and these appear to move around on footwear, machinery, digging tools and on muddy animals, particularly feral pigs. Pigs root in the infection zone, disturb kauri roots and can spread spores through their gut into new catchments. Pigs are a significant vector for other soil-borne Phytophthora diseases in many countries.

How you can help

The joint management team of the Ministry of Agriculture and Forestry, regional councils and the Department of Conservation has guidelines to minimise PTA spread:

  • All footwear, tools and equipment/machinery must be totally soil-free when entering a kauri forest. Trigene disinfectant will not kill PTA embedded in soil.
  • Wheeled or tracked machinery and vehicles are high risk and must be given special attention to ensure they are free of any soil.
  • Stay away from kauri tree roots as much as possible.

Auckland Council has been the most proactive, requiring foot and vehicle cleaning throughout the Waitäkere Ranges parkland. Most track entrances and intersections have spray bottles and mud cleaning gear, so walkers can keep their footwear clean of kauri PTA.

DOC has stepped up its work to protect the internationally important kauri forests in Northland, especially Waipoua, and to stop the disease getting to the Coromandel and Kaimai Range. But muddy tracks are high-risk pathways for spreading PTA, and many poorly
maintained tracks in the Waitäkere Ranges are undermining the excellent work by Auckland Council’s biosecurity staff to stop PTA spreading.

Across Northland and Auckland, local forest reserve managers are failing to address problems with diseased kauri or stopping the disease getting into their kauri forests.

A major problem is coming from kauri forests on private land in the north. Biosecurity staff have inspected 300 private forest areas and offered assistance in Auckland, but nothing has happened in Northland and it is only starting in the Waikato. All Forest & Bird kauri forest reserves with walking tracks have cleaning stations for boots.

Logging spreads problem

MAF’s indigenous forestry group has added to the problems of PTA spreading in private kauri forests. Forest & Bird members in Northland noticed MAF staff actively encouraging landowners to log remnant forests in Northland, so they requested copies of MAF logging
permits. They discovered that the MAF permits had no requirements on logging contractors to clean machinery of mud or restrictions on logging in areas affected by
kauri PTA.

Compounding this, MAF’s foresters have had no training to identify PTA and seem ignorant of MAF biosecurity procedures to control the disease, even when they share the same office.
Most logging contractors in Northland move around several sites and some come from the central North Island.

The risk of PTA being spread throughout Northland, the Coromandel and Kaimai Range is very high. The most effective measures to minimise the spread of kauri dieback are through regulations under the Biosecurity Act.

Despite MAF biosecurity taking a lead role for four years, they still need to deliver a National Pest Management Strategy or a Pathway Management Plan (under the Biosecurity Act) with disease movement controls across the northern North Island to stop PTA spread, and
strict controls for PTA in MAF logging permits.

Also, the Regional Pest Management Strategies still have no rules for PTA control on private land. The most effective controls to save private kauri forests may come from Regional Pest Management Strategies under the Biosecurity Act. But there are still no rules for regional councils in any of the Regional Pest Management Strategies either.

The joint agency experts are relying on an under-resourced education programme to stop the spread of PTA, but would we rely on an education programme to prevent the spread of a killer disease like smallpox?

As a nation we are in denial about the risks of alien diseases to our precious heritage and our economy. We have been reluctant to stop the spread of pests that pose huge risks to our fragile economy because senior officials and politicians aren’t prepared to control a very small number of people spreading them. We all bear the costs of this with higher taxes.

With PTA, we stand to lose our national icons, like Täne Mahuta. This foot-dragging could continue to consign rural areas in Northland to on-going poverty, as their
new Kauri National Park is killed off through inaction.

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