Precision spraying wins acceptance

Department of Conservation ranger Brenton Wilson watches a helicopter make a pass to spray...
Department of Conservation ranger Brenton Wilson watches a helicopter make a pass to spray wilding pines, with Fernhill below. Photo by Guy Williams.
Drive or fly into Queenstown from the west, like most visitors do, and turn your gaze left then right, you will see sharply contrasting landscapes.

On the left, the bare tawny flanks of the Remarkables Range; on the right, hillsides shrouded in the bottle green of conifer trees.

Mark Nelson would like to change that. The Wakatipu Wilding Conifer Control Group (WCG) operations manager says the wilding trees may make Queenstown look like a ''postcard from Canada'', but form a sterile monoculture that suppresses native plant and invertebrate species.

He would like us to think of the Wakatipu as less Banff, more Scottish Highlands.

Mr Nelson, a Department of Conservation (Doc) ranger brought over from the West Coast to manage the WCG's eradication efforts, is standing atop a ridge overlooking the Queenstown suburbs of Fernhill and Sunshine Bay, gesticulating to make his point.

Below, a Nokomai Helicopters aircraft with a boom attached is flying low over a vast wilding forest that extends down to the houses, dropping herbicide in precise passes.

It is January 9, and Mr Nelson is watching the treatment of a 28ha ''containment line'' along the upper reaches of the forest on Ben Lomond. The trees are mainly Douglas fir with some Corsican pine - both prolific seeders.

No-one is interested in harvesting the trees for commercial gain, he says.

''Even firewood contractors won't touch it.''

It would cost an estimated $18,000/ha to log the trees commercially. Aerial control of a dense forest of this type costs about $860/ha.

The two-and-a-half-hour operation is a small but highly visible part of a $1.4 million, joint WCG and Doc programme this summer to prevent wilding trees spreading beyond the 73,000ha of land in the district already infested.

Ground operations began in September and will continue until April, but the more cost-effective aerial programme began in the Skippers Canyon in early December and should be completed by the end of February.

It is the second year of a five-year, $5 million offensive to turn the tide against the district's wilding tree problem.

Mr Nelson says when people hear the word ''spray'', they think of mist sprayers in orchards. However, WCG aerial operations use a helicopter fitted with a boom that releases the herbicide - mixed with water, penetrant and canola oil - through nozzles that minimise drift by generating large, heavy droplets that ''fall straight down''.

That means creeks, water takes for domestic use and stands of beech trees and other natives can be avoided with a high degree of accuracy.

A ''bucket-load of work'' goes into each operation, he says. Before the Ben Lomond spray job, Doc staff walked up every creek on the hillside from the bottom, logging GPS co-ordinates and shooting video and photographs in order to set buffer zones.

Throughout the morning, two weather observers record windspeed, humidity and temperature at 30-minute intervals. If maximum tolerances are exceeded, work must be suspended.

Because of the operation's ''sensitivity'', mainly due to its visibility from urban Queenstown, it is being observed by an independent auditor.

Following a public meeting about the operation in October, five Fernhill households have asked to be informed in advance about when it takes place.

Mr Nelson says aerial operations have been carried out on private and Doc land in the district for eight years, but have only entered the wider public consciousness in the past couple of years as wilding forests close to urban areas and highways have been controlled.

It takes up to two years for the trees to die, and an unknown period for them to break down or ''melt''. He accepts many residents dislike the appearance of dead trees, but believes it is ''short-term pain for long-term gain''.

He encourages anyone with concerns about the programme to ''just come and talk to us''.

''Our mission is not to convert everybody, but to give them the facts so they can make their own minds up.''

WCG co-chairman Peter Willsman says the trees have been steadily advancing up the Ben Lomond ridge, threatening other parts of Ben Lomond Station.

''Once the seed goes over the top, it's a never-ending problem.''

He thinks the public is becoming better informed and more accepting of the WCG's work.

''There's a growing awareness of the issue, and most people are resigned to the nasty visual effects.''

Work in the past five years to optimise the combination of spray recipe, helicopter air speed, nozzle design and nozzle pressure has ''revolutionised'' aerial operations, Mr Willsman says.

By the end of the current five-year programme, most seeding trees in the district will have been destroyed, and a control phase will begin.

Could Queenstown Hill one day be restored to tussocks and grasses or replaced with native forest?His generation is ''holding the issue in check'' so the next generation can take the next step of restoration.

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