Geoff Cumming talks to ecologists fighting the extinction of our forest giants

Reports of Tane Mahuta's demise may be premature but death could be just a stray boot away. The dieback disease threatening the forest kings of northern New Zealand is as bad as it gets: once the algae-like microbes infiltrate the kauri's root system, there is no cure. By the time symptoms show - leaf yellowing, canopy loss, withered branches, bleeding lesions and collar rot - it is likely too late.

Talk to scientists and agencies beavering away on the response and the messages are at once frightening and encouraging. The disease is a new species of phytophthora, from the Greek for plant destroyer. Different strains have devastated everything from strawberries, tomatoes and potatoes to forest giants like jarrah in Australia, oak trees in Europe and North American chestnuts.

The soil-borne variety attacking our kauri, known for now as PTA, has spread to 11 per cent of kauri stands in the Waitakere Ranges. It has footholds in the Waipoua Forest, home of Tane Mahuta, on Great Barrier Island (where it was first observed in the 1970s but mis-identified), in the Russell Forest and on private bush lots in Auckland and Northland. These potential giants, capable of living well past 1000 years, are on death watch.

What researchers don't yet know is how fast the disease progresses and whether some kauri may prove more resistant than others.

Advertisement

The kauri is taonga to Maori and European alike. The New Zealand native has spiritual significance both for its form and function. Maori regard it as a rangatira (chiefly) species because of its ecosystem-supporting role - many other species depend on it. They used the hardwood for canoes and the gum for torches. European exploitation for housing, shops,furniture, ships and pleasure craft reduced an estimated 1.2 million ha of kauri to around 7000ha.

As things stand, we could lose what's left, says Auckland Council biosecurity manager Jack Craw.

"I've worked in this game for 35 years and I've never met a pest as tough as this; it's like stoats, rats and possums all rolled into one. It's capable of extinguishing a species on its own, and not only kauri but the ecosystems they support."

But there is hope, passion and commitment in the response under way. It is a rare example of Crown research and university scientists, councils and iwi working well together, uniting around a national totem. Their work, however, needs ongoing funding and Wellington is antsy that no cure is in sight. The science effort is well-supported for now but a joint-agency steering group, involving councils, DoC, iwi and MPI, is under a cloud.

Iwi are calling for a more holistic approach and a community-led response has Churchillian appeal - but how to get there? A symposium in Auckland today aims to bring the public up to speed with the scientific response and perhaps lead to greater public support and involvement. Organisers hope to make it an annual affair - the microbe is here to stay.

The inaugural meeting has drawn a world authority on phytophthora diseases, Professor Giles Hardy from Murdoch University in Western Australia. A frequent visitor to our forests, he raises hope and alarm in equal measure.

"Knowing how phytophthoras work, it would be very sad to see them go. Even for a Western Australian, those big kauris mean a lot. They are one of the tallest conifers in the world; to let them disappear would be a terrible thing. But unless you come up with effective treatment regimes, your children and grandchildren will likely not see these trees in many areas."

The largest known surviving kauri, Tane Mahuta - 50m high and 14m round and thought to be more than 1500 years old - draws foreigners and locals like a pilgrimage. But spores have crept to within a couple of hundred metres of the tree and reports place it "at grave peril". Closing off access is an option, though local iwi Te Roroa, while worried about the health of the forest, fear the impacts of a tourism downturn on local communities.

Hardy says much more can be done to stem the spread of the disease. Community-led efforts in Australia have thwarted a phytophthora threatening jarrah in many areas, with contributions ranging from education and monitoring to chemical spraying. We are not quite there yet - interest groups and iwi are clamouring to help but the call to arms must await the right weapons, appropriate training and good co-ordination.

Some of Hardy's proteges are in the vanguard of the science response involving Landcare Research, Plant and Food, forest research agency Scion and the University of Auckland. Scion's focus is on developing dieback-resistant seedlings for replanting in infected areas. Phytophthora experts Dr Peter Scott and Dr Nari Williams are leading the cutting-edge lab work, boosted by new funding from the Ministry of Business, Innovation and Employment. They acknowledge that kauri's slow growth rate means it will be several human generations before new plantings resemble the forest giants of today - but the alternative may be far worse.

A shorter-term band-aid looms in a booster injection, using phosphite to help trees build resistance to the disease. Used successfully against overseas phytophthoras, the chemical could buy time, hopefully slowing PTA's progress in infected trees and boosting immunity in non-infected stands. Trials led by Plant and Food scientist Ian Horner are showing promise. The trials take time - though injections could become an option for private landowners within a year. But Horner and others worry about enthusiasts overdosing and doing more harm than good.

DoC has spent $1.5 million on boardwalk and track engineering improvements but funding for next year is uncertain. There's even potential for a dieback sniffer dog, to detect spores in soil before infestation.

But by far the best biosecurity response at this point, says Craw, is to stop the spread of PTA. The spores are spread by soil movement - potentially by trampers, mountain bikers, pigs and pig hunters, bird watchers, forestry workers, earthmovers, other vehicles, farmers and other landowners - as well as by water. No easy task then, but hard nuts such as pig hunters in the Waitakeres are on board, spraying their dogs as well as their boots. A council-funded culling programme has reduced feral pig numbers by 70 per cent, improving bush health.

But those refusing to wash boots with disinfectant when entering and leaving tracks; not keeping to boardwalks despite clear signage and ignoring track closures are the problem. A survey published mid-year found sanitation compliance rates in the Waitakeres were below 40 per cent and Aucklanders, not tourists, were the culprits. Things have improved slightly but are way short of the "high-90s" level sought, Craw says.

If kauri is as important to national and local identity as most acknowledge, why not heed the messages? Craw concedes there's a gulf between the agency response and the wider public's recognition of what's at stake. Complacency on one hand and fatalism on the other may be factors. More likely, people see withered branches surrounded by apparently healthy bush and don't recognise the insidious nature of this disease: like a cancer, symptoms may not show until it's too late.

"We've been constantly in the media but we've really failed to get the message across that we are the problem.," says Craw. "We've established that people love kauri and hate the disease but that hasn't translated to behaviour change in the community."

"Education doesn't necessarily bring about support," says Social scientist Marie McEntee of Auckland University's environment school. She says decisions to close tracks in disease-free areas and prohibit use of the Hillary Trail for a running event were poorly understood and provoked resentment. Though the council has held 140 public meetings and more than 200 workshops, that doesn't equate to engagement with local communities. "The council needs to take the plunge and get people involved. Science alone can't solve the problem."


• The symposium is at the Auckland University Engineering School, 22 Symonds St, 9.30am to 5pm.