These guys are clearly born survivors. Right up on the skyline of the scree slopes above Cragieburn ski field in Canterbury's Porters Pass, a gaggle of contorta pines are sprouting away like a happy little family of Christmas trees.

Or at least they were until helicopters with herbicide tanks and spray booms arrived last year for the start of a national $16 million wilding conifer control programme.



Now their green foliage is turned half-brown. In another few years, they will be grey tree skeletons, a stand of bleached spars poking up in the landscape. But still, it is amazing where conifers will root.



Christchurch forestry consultant Owen Springford says you have to understand the ecology of pines. They evolved to colonise the bare ground of the retreating North American glaciers following the last ice age.



So they love the fire-razed and denuded mountain ranges – what we think of as the natural tussock land – that make up of much of the South Island's iconic golden landscape. No wonder their spread is on an exponential curve, threatened to cloak every slope and gully with a dark green blanket.



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​And getting controversial, Springford says perhaps that is not such a bad fate. Or something which – because we can't cost-effectively stop it – we ought to be managing to our advantage.

JOHN MCCRONE/FAIRFAX NZ A gaggle of sprayed wildings turning brown high up the scree slopes above Craigieburn ski field.

Setting out his case in a paper for the Landscape Foundation in March, Springford says New Zealand has been putting off real climate change action by relying on carbon offsets from its 1990s wave of forestry planting. A "wall of wood" was created that locked in credits.

But that is coming up for harvest from 2018. The country is going to be in a deep financial hole if the world does get real about enforcing the carbon commitments contained in the 2015 Paris Agreement.

And yet wilding conifers – if allowed to continue their current takeover of parts of the back country and conservation estate – could become a carbon sink that pays for itself, Springford says.



"Wilding forests provide the best hope for New Zealand to meet the Government's currently stated goal of a net 5 per cent reduction on 1990 emission levels by 2030," he writes.



Of course his view is not widely shared. Even his forestry colleagues say Springford is out on a limb with this one.



However it shows there are big questions developing over what New Zealand can do about its runaway exotics and whether it is thinking that clearly about its conservation policies.



The same issue was raised in a different context this week at a Wellington biodiversity conference, Crazy & Ambitious, called to discuss the Government's eye-catching Predator Free 2050 promise.



In a science challenge so bold it is being compared to a New Zealand Apollo moon-landing programme, the goal is to find technologies which can rid the country of possums, rats, stoats and other killers of native wildlife within the next 30 years.



Yet some panellists, like Greater Wellington Regional Council biodiversity advisor Dr Jamie Steer, were asking if this is New Zealand again being hopelessly idealistic.



As with the costly campaign against wilding pines, Steer says there is a Garden of Eden mentality where New Zealand greenies – the hippie baby-boomer generation – are still dreaming of rolling the countryside back to a time before human settlement.

JOHN MCCRONE/FAIRFAX NZ Ghost trees on a former forestry research plot at Cragieburn. The dead spars will take years to rot down

But he says world groups like the Ecological Society of America are beginning to accept that game is already lost. With climate change, population growth, a globalised economy, the Earth has entered the "Anthropocene" era where humans have altered nature for good.

Across the planet, everything is going to be left a mongrelised mash-up of native and exotic ecosystems. The forces unleashed are too overwhelming.

So in that light, especially given New Zealand has let in more invasive species than just about anyone, it can't afford to base its national policy on impossible outcomes. It needs to stop kidding itself and treat problems like wilding conifers a little more creatively.



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People are starting to notice the mess. Especially where it has begun to threaten the "autumn colour".



The Cragieburn range is a hot-spot for wilding trees because from the 1970s to the 1990s, it was a trial area for the New Zealand Forest Research Institute. The scientists were planting plots of every kind of introduced species to see what grew well for wood or to control erosion.



So in effect they were identifying those best suited to race away across the countryside.



Some conifers – like the larches – made for an attractive seasonal display alongside the highway to the West Coast, turning yellow and shedding their needles. Now the research plantations have become hillsides of grey skeletons.



The same along similar drives like the Kawarau and Shotover gorges heading into Queenstown or the road up to Aoraki/Mount Cook.



Retired Scion researcher and member of the Waimakariri Ecological and Landscape Restoration Alliance (Welra), Nick Ledgard, says he was in Queenstown recently to talk about wilding conifer control there.



"I'm surprised there hasn't been more comment," he says. With spraying, the backdrop to the Shotover River and Skippers Canyon has been changed radically.



He met a photographer with the job of shooting a new district calendar. "In one photo, 80 per cent of it would have been dead larch."



And while Ledgard is a strong supporter of wilding control – that is the reason Welra was formed – he says the current plan is rather sketchy, especially about what people expect to grow back in the next few years in place of all these dead trees.

TONY BENNY/FAIRFAX NZ Community action: Forestry researcher Nick Ledgard (left) with Welra chair, Ray Goldring, in the Waimak basin.

The threat of wilding conifers has been recognised for a long time. Particularly with species like the scrubby contorta pine, the larch and the Douglas fir that have light, easily blown, seeds, a single mature tree on a high outcrop can sew a whole range.

Ledgard says it doesn't happen every year. With contorta, the number one scourge, it takes ideal conditions – a big wind storm coupled to a wet growing season.

"The cones only open for a few weeks. So the parent seed source could be producing cones for 30 years and then, just once in that time, things were going in its favour and a crop of trees have come up."



But due to early neglect, the spread of wilding conifers is now increasing exponentially. Department of Conservation (DOC) graphs show the trend-line lurching skyward since about 1990.



The areas of established thickly-wooded wilding forest are still relatively small– a few hundred thousand hectares. However another 1.5 million ha are now liberally sprinkled with seedlings and saplings.



That is where the golden landscapes will soon become dark green blankets without a concerted campaign of action.



DOC says with 5 per cent more land being covered every year, a fifth of the country could be taken over within the next 20 years. So the pace is indeed dramatic.



Some money was being spent on control measures for a long time. DOC has been going out with chainsaw gangs to chop down mature trees overlooking valleys or big specimens in farm shelter belts. But it lacked the budget to tackle the knee-high crop coming up across much of the high country.



Efforts became more serious a decade ago as volunteer community groups began to be formed with the encouragement of DOC and local councils.



The Wakatipu Wilding Conifer Control Group in Queenstown was among the first. Now there are many similar organisations like Welra in the Waimakariri basin, and others in the Marlborough Sounds and Southland's Mid Dome.



Citizen armies have been out in the hills at weekends using their own slashers and chainsaws against the advancing trees.



But Ledgard says the campaign has finally got proper momentum because a couple of years ago Treasury was sold on the logic of attempting a king-hit on wildings.



There is no doubt their spread has to be stopped, Ledgard says. They are taking over productive farmland. They suck up water. They are bad for biodiversity – little else can live in the thick gloom of a pine stand. They would turn the mountain ranges ugly.



And to take them out now as immature saplings is going to be a lot cheaper than waiting until they are a solid mass of mature trees.



Ledgard says it helps that new herbicide brews have come along which can be either sprayed from the air using booms and wands, or dabbed on the base of a tree from the ground. That has completely changed the economics of control.



So in 2016 the Government announced its $16m programme which will run for four years. "Particularly if we work from west to east – following the prevailing winds – we can clean up areas that will never be invaded again because there'll be no seed source," says Ledgard.

SUPPLIED/KIERSTEN MCKINLEY Volunteers rooting out wildings near Omarama. The feel-good factor of doing something for conservation.

In fact the plan is containment rather than full eradication. Ledgard says an awful lot more money would be needed to eliminate every last tree. Besides which, some wilding species like Douglas Fir are legal plantation crops.

However the plan is to take out the priority spots and so halt the spread in its tracks. Which sounds promising. It is good news from the conservation point of view, Ledgard says.

But the question people are now waking up to – as they see the patches of sprayed hillside turning brown and grey – is what is going to grow back in the conifers' place? With no strategy there, it is likely to be mostly just other kinds of exotic weeds, Ledgard says.



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Part of the argument of Springford and others – like former All Black lock and retired geologist, Peter Whiting of Wanaka – is that there is a basic confusion in the public's mind.



The obvious answer on regrowth is that where wilding areas are not farmland, they are best returned to native bush or tussock. But New Zealand's ecology has already been altered by its 700 years or so of human habitation.



Whiting, who has been penning recent opinion pieces about the possibility of letting larch and Douglas fir just go native, says before Maori arrived and put fire to Central Otago, it was largely totara forest all the way up to 1200m.



Tussock only existed at the very tops of the hillside vegetation. Trees are what want to grow across most of the South Island, he says.



Another uncomfortable truth, point out others, is that wilding conifers are just the first wave of an exotic tree invasion. They are being followed now by the many ornamental trees imported by keen New Zealand gardeners, like cherries, rowans, hawthorns, birches and sycamores.



If they have winged seeds or a fruit enjoyed by birds, there is a queue of other potential back country invaders lined up.



Alan Ogle, a colleague of Springford at consultancy Southern Forestry, says one of the problems is that because community groups – the weekend squads with their secateurs and loppers – have got so involved in wilding eradication, an emotional investment in getting rid of every last tree has developed.



"There's a feel-good factor there because they are actually doing something positive and getting good exercise while they do it."



But Ogle says re-establishing anything native is going to be another whole mission in itself. "Without a succession plan, the outcome for areas like Cragieburn will be at best no wildings – and a lot of gorse, broom and blackberries instead."



The Government's official response is that Welra's volunteers are likely to do the follow-up. Mountain beech is what naturally forests the area and teams of helpers could plant out seedlings.



However Welra's Ledgard says it is not so simple. He says a dying wilding forest does make a perfect half-shaded nursery for beech. So there is certainly a window of opportunity to do that during the next couple of years.



But Cragieburn has rabbits, possum and deer that will be nibbling away at the tender seedlings. The effort and the cost looks prohibitive without a proper replanting programme.

BARRY HARCOURT/SOUTHLAND TIMES Autumn colour in Arrowtown. The dark green of Douglas firs is now marching down the hill.

In Queenstown – focused by the need to take a decision on what the council should do with its own 170ha Douglas fir plantation on Coronet Peak above Arrowtown – the debate has been taking yet another direction.

Ironically, the firs are a source of wilding seed that is rapidly invading Arrowtown's own famous exotic blaze of autumn colour – the hillsides of sycamore, larch and rowan that have become such a tourist attraction.

Queenstown developer and chair of the Wakatipu Wilding group, Grant Hensman, says the taller evergreen Douglas fir are marching down and taking over as they can shade out their deciduous rivals. "In 20 years time, there will be no autumn colours if nothing is done. The firs will smother it and it will all be green."



So Hensman says one proposal is to replant the council plantation with these other exotics, create even more of that autumn colour right up the mountain.



It is not so crazy because this time the council could choose species which are not prolific spreaders, or even sterile cultivars.



Hensman says there are the same replacement possibilities if the pressure comes on to tackle the thick conifers planted as a backdrop to Queenstown itself – originally to control erosion and also give it a European alpine resort look.



Hensman says those Douglas firs are just as much a seed problem – the source of the wildings appearing all outside the town now. "The community has to make a decision on that. Do they want to be paying a maintenance bill forever to keep them?"



Yet there are alternative species like spruce which are not such a wilding issue, he says. So managed right, exotics could have their place as an attractive landscape alternative.



★★★



This is Steer's Anthropocene argument. Turning back the clock to a time before human arrival is impossible for New Zealand. Some kind of ecological compromise is inevitable.



So the game plan for wilding conifers has to be understood in that context. And one thing about keeping some forests as tourist attractions is there will be the money to pay for their proper management.



Springford says this is his point about using wildings as a carbon sink. Conifers don't invade healthy beech forest. They only take over bare land poor in nutrients. But give them a few generations and they will build up a layer of soil that could then provide a seeding bed for the return of native trees.



So why not manage tracts of the back country – the other sides of the ranges where only pig hunters ever go – as contained carbon forest? The value of the credits would mean there was then the cash to follow through later with a serious native bush regeneration plan.

SUPPLIED Queenstown's alpine forest backdrop is attractive to visitors. But it is another wilding seed problem.

"Rather than fight Mother Nature, the strategy should be to work with her by encouraging wilding forest to develop and then promote the succession of native forest within these wilding forests," he says. The alternative is mass spraying followed by a blow-out of briar, broom and gorse.

Others like Ledgard respond that no-one wants a dense thicket of wildings across the Waimakariri Basin or Mackenzie Country just because they will happily grow themselves. "He'd be about the only person."

And he says Springford is painting too rosy a picture of how natives would eventually grow through after the wildings had improved the soils.

Ledgard says it does happen in parts of the North Island where there are Pinus radiata plantations that have been thinned, and there is plenty of rain and good sources of native seed. "But that's talking about a very different situation."

Yet it is also obvious that the current mass helicopter-spraying campaign is only step one. It has created a lot of dead and dying trees. The follow up question is what can be done next with the land which makes both ecological and economic sense.

And, as he says, there is not much time for making up minds as there are more than enough other exotic invaders – both old ones like gorse or browntop grass, and new ones like sycamores – queued up and waiting their chance to claim a spot on the New Zealand landscape.