A tree once sold to New Zealand as a saviour of crumbling hillsides has become the worst weed in the South Island, with contorta pine now spread across close to a million hectares of high country, farmland and conservation land.
Contorta, also known as lodgepole pine, was brought in from western North America and planted with enthusiasm through the middle of last century to hold back erosion, provide timber and shelter paddocks from the wind. What looked like a clever fix has turned into one of the country’s most expensive and stubborn environmental problems. The species has adapted fast to local conditions and now seeds itself far beyond where anyone ever planted it, marching up tussock slopes and across river flats at a pace that has alarmed scientists and landowners alike.
Retired tree scientist Nick Ledgard, who has studied the species for decades, told RNZ that contorta “was thought to be a bit of a wonder tree, but it’s turned out not to be the case”. The trouble is in the seed. Each cone can carry up to 70 seeds, and those seeds mature within four years and travel huge distances on the wind. Ledgard described the spread simply. “It’s like dust in the wind.”
That biology helps explain how a handful of planted stands became a landscape problem. Wilding conifers, the broad group that includes contorta along with several other introduced pines, larches and Douglas fir, now affect more than two million hectares across New Zealand. Before a coordinated national control effort began, the trees were claiming around 90,000 new hectares every year. The Mackenzie Basin, Molesworth Station, the Craigieburn Range in Canterbury and stations around Lake Pukaki have all been hit hard, with dark green forests creeping over country that was once open golden tussock.
The damage is not only about how the land looks. Dense stands of wilding pines draw large amounts of water out of river catchments, which matters in the dry eastern South Island where every drop counts for farming and for the rivers themselves. The trees also change the chemistry and biology of the soil, leaving an acidic monoculture where little native plant life can survive. Tussock grasslands and pasture that supported sheep, native insects and ground-nesting birds get swallowed up and shaded out. Once a slope is fully covered, the open high country character that defines much of the South Island simply disappears.
Pulling the trees back has been a long and costly campaign. Central government has spent at least $100 million on wilding control over the years, and regional councils have put in roughly the same again. In this year’s Budget the government pledged a further $79 million towards the work, a sign that officials see the fight as far from over. The National Wilding Conifer Control Programme coordinates the effort across the country, matching central money with regional council and landowner contributions and trying to stop the trees before they reach seeding age.
On the ground the work is unglamorous and relentless. Crews and volunteers walk the hills pulling out seedlings by hand, spraying larger trees and felling mature stands. Forest and Bird volunteer Aiden King, who has spent 20 years on the job, said the tide may finally be turning in some places. “It feels like we’re winning now,” he told RNZ, a rare note of optimism after years of watching the green wave advance.
The hardest part, ironically, comes at the end. Ledgard warned that knocking out the bulk of an infestation is not the same as finishing it off, because even a few survivors can reseed a cleared slope within a few short years. “The last few percent have got to be got rid of,” he said. That means areas declared clear still need to be walked and checked for years afterwards, and a single missed tree can undo a season of work.
Some landowners are looking for ways to make the removal pay for itself. At Pukaki Downs station, manager George Ormond described clearing whole forests rather than spraying them piece by piece. “Instead of spending money using spray, this way you get completely rid of the forest,” he said. Felled trees are increasingly being chipped and turned into biofuel, with energy company Pioneer Energy among those taking the waste wood, so that a problem on the hillside becomes fuel for a boiler instead of a bonfire.
The wilding pine story carries an uncomfortable lesson about good intentions. The same fast growth and hardiness that made contorta attractive for erosion control are exactly the traits that let it run wild once it escaped the plantation fence. Scientists now talk about the right tree in the right place, a phrase that sounds obvious only with the benefit of hindsight. For the farmers, volunteers and council crews still climbing the South Island’s hills with loppers and spray packs, the wonder tree is simply a weed that refuses to give up.
Have you seen wilding pines spreading across country you know, or joined a control day to pull them out? Share your experience in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job π
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