Hope for our dying kauri

Two thousand years ago, some of the gigantic kauri trees that tower in Northland’s Waipoua forest were seedlings breaking through the forest floor.

By the time the first humans arrived here in canoes from Polynesia, they had already grown into massive, established trees more than 1000 years old. Over the following centuries, they presided silently over more arrivals, human and animal alike, and many disappearances, including the extinction of the moa and the vanishing of the kaka from Northland’s forests.

Now those ancient kauri themselves are at risk of disappearing – not from old age, but from a virulent fungal pathogen too small to be seen with the naked eye.

Kauri dieback was the name given to the disease that was first noticed sickening kauri on Great Barrier Island during the 1970s, but the actual pathogen responsible (Phytophthora Taxon Agathis, or PTA) wasn’t formally identified until 2008. Infections start in the roots of the trees, rotting the wood tissues that transport nutrients, leading to yellowing and loss of leaves and branches, thinning canopies and lesions around the trunk that bleed kauri gum.

At the moment, it’s a death sentence for any kauri infected, with thousands of the trees lost over the past decade. Today PTA has spread to within 500m of our most famous tree, the mighty Tane Mahuta.

What’s being done?

Considering that New Zealand’s current kauri population is, by various estimates, only one to four per cent of what it was when humans arrived in New Zealand, PTA is a serious threat to the future of the species.

“There once was a million hectares of kauri, and now there’s less than one per cent in old growth, less than 10,000 hectares,” says Stanley Bellgard, a plant pathologist with Landcare Research in Auckland.

Stanley and the team at Landcare are part of a joint agency response racing to find a way to combat kauri dieback under a $6 million funding grant. At the moment, the pathogen has been found in forests from Auckland northwards. “At this point, the large tracts of kauri along the Coromandel and in the Hunuas are free of the pathogen,” says Stanley, which is the way scientists want it to stay (see What can I do? below).

With funding for the project expiring in June next year, the joint agencies are preparing a business case for Cabinet for extended support; a case that can be hard to make when a tree species does not have horticultural value.

“Who has that magic metric of the economic services provided by trees?” Stanley asks. “Trying to ascribe a value to that ecosystem function is ultimately the only way that economists or the government will respond, when they see there is a return on investment. If there was a threat to Pinus Radiata, you’d see a huge [governmental] response to a forestry species pathogen.”

Future forestry?

One person who believes there is an economic case to be made for kauri forestry is Mathurin Molgat, a Canadian-born transplant to New Zealand, whose film Song of the Kauri has been touring New Zealand and international festivals this year. The film explores the wide-scale devastation of kauri forests throughout last century for timber, quoting forestry professor Sir David Hutchins who called it “one of the great crimes of the Anglo-Saxon peoples”.

Yet Mathurin believes that managed correctly, growing kauri as a forestry resource is the way to save the species. “Kauri forestry would differ to pine in that you wouldn’t grow and clear-cut and regrow, but grow and cull at a certain percentage,” he explains. “In Europe they do it very successfully.” He suggests 10 per cent of trees could be culled at the 60-year mark, a time of acceptable maturity suggested by Scion Research in Rotorua. “The great thing about kauri forest is that you would have biodiversity, unlike in a pine forest.”

While some private farmers have already started their own kauri plantations, with one grower in the Far North holding over 10,000 saplings already, Mathurin says the government would need to invest to make it a serious economic proposition, with the main appeal being to long-term superannunation-type funds, although fund hedging could be a shorter-term economic option.

For now, Stanley Bellgard hopes the government will look at the kauri dieback research project as having a bottom line that includes spiritual and cultural values as well as economic. “Tane Mahuta is a cultural icon, the Lord of the Forest,” he says.

“1.3 million people from around the world make the trek to see that tree every year. But aside from the tourism aspect, it’s something people identify with. It plays an intrinsic part of the economic, historical and cultural identity of Northland.”

A kauri cure

In one of the most exciting developments in biological fungicides this decade, scientists at Biotelliga, a Pukekohe-based company that develops natural crop protections against pests, are in their third year of testing an environmentally friendly fungicide that has potential to cure kauri dieback.

The fungicide was discovered by accident about four years ago at Auckland University when a fungus that was being tested as a food colouring escaped in a lab, and killed off all the other fungus samples. The scientist in charge recognised its potential as a natural fungicide and sent it to Biotelliga, which processes trillions of fungal spores a year for testing.

“We examined its structure and properties and tried to get it to control other fungi,” says Steven Ford, part of the team working on the project. “We discovered that the fungus was producing a novel metabolite, and that metabolite has so far controlled every single fungus we’ve put it against. But more beneficial than that, we found it had a very favourable toxicity to mammals.”

In layman’s terms, that means it will kill other fungi without making people sick (unlike many chemical fungicides today). And as it’s an indigenous fungus that’s already in New Zealand’s ecosystem, it also doesn’t appear that using it would affect the broader environment.

The team tested the metabolite against PTA, and “lo and behold, we found that PTA is very susceptible to the metabolite, so we are now two years into building a specific formulation of the metabolite to control kauri dieback disease,” says Ford.

The team still have around another year of lab and field-testing before they plan to offer it to the Department of Conservation as a potential treatment, but things are looking hopeful. If the trials are successful it could be a young biotech company that’s responsible for saving some of this country’s oldest living residents.

Fast facts: Kauri

• Scientific name: Agathis Araucariaceae
• Ancestors of the kauri appeared in the Jurassic period (135-190 million years ago), making it one of the most ancient trees in the world.
• Height and width: Around 30m with a 3m trunk at maturity, though some specimens are up to 60m tall and 7m wide.
• Tane Mahuta is the largest living kauri, with an estimated wood volume of 244 cubic metres. Cut trunks suggest there were larger kauri felled by European settlers.
• Young kauri are known as ‘rickers’.
• Burnt, powdered kauri gum was once used in tattooing.
• ‘Swamp kauri’ logs dredged from peat swamps can be up to 50,000 years old, yet remain in excellent condition, and are often used for furniture.

What can I do?

• When in the bush keep an eye out for trees with symptoms of kauri dieback – yellow leaves, dead branches, bleeding gum at the base, thinning canopies – and report suspected infections to the Kauri Dieback Management Team on 0800 NZ KAURI.
• Stick to defined tracks, and keep dogs on a lead so they can’t walk on kauri roots.
• Scrub boots and shoes after bush walks.
• Fence livestock out of kauri forests.
• Use extreme caution when using earthmoving equipment near kauri forest, as soil transfer spreads weed seeds and harmful fungi.

Visit Keep Kauri Standing www.kauridieback.co.nz for more information.