Wilding pines should be used as a sustainable resource, Jim Childerstone writes.
It is ironic that a football pitch-sized patch of forest is being lost throughout the world every minute, yet in New Zealand hundreds of thousand of taxpayer dollars are being spent in a never-ending battle against wilding conifers.
Let's get practical and use these trees as a sustainable resource as well as for carbon sequestration.
The nation's forestry estate involves introduced exotic conifers of various species. It's our fourth-biggest industry.
So why all the hype about conifer eradication? Our landscape has been extensively modified over the past 200 years, anyway.
Why not manage this invasion as a resource And an income source for controlling spread?
The prime culprits are Pinus contorta, Pinus silvestris (Scots pine), P. nigra (Corsican) and Douglas fir (NZ Oregon).
Contorta and silvestris were introduced by us old foresters as slip control on steep mountain faces back in the 1940s and '50s.
It actually worked (partially).
But their regenerating ability was phenomenal, not only fringe spread but seeds blown by the wind for kilometres.
Three pest species have marched well beyond the Queenstown, spreading up the lakeside and into the Harris Mountains.
Within the periphery of Queenstown and around some of the early gold-mining sites, Douglas fir has found the right conditions to establish.
This species also makes up a considerable percentage of managed forestry throughout the South Island.
It is a premium timber tree, fetching top prices for construction purposes.
Around the flanks of Ben Lomond and Queenstown Hill, regeneration of Douglas fir is basically on the fringes of seed-bearing trees.
Seedlings will establish at more than 50 a square metre.
On one measurement I counted more than 100 30mm to 100mm high seedlings.
They are prolific.
And they cost nothing to grow.
In a managed, commercially grown plantation, seedlings are planted at around 1400 stems per hectare, and thinned down to about 400 sph.
So what can a bit of silviculture work on Skyline Hill produce?
My first report to the then district council headed by Mayor Warren Cooper in 1997 recommended a limited harvest (about 3 hectares) on the main terrace above the Skyline track.
Logging contractors from Balclutha attempted a partial clearfell and select felling operation.
The net yield was close to $200,000.
I recommended part of this amount should go into forest management and establishment of amenities.
Since then, several small-scale logging operations have occurred with the object of managing a forest for income purposes and (hopefully) control of fringe spread.
I understand this may be continuing. Some areas had been replanted with non-invasive sequoia species.
Many years earlier (1970s) I milled hundreds of cubic metres of Douglas fir up on Fern Hill and Sunshine Bay.
Builders were virtually lining up for building grade framing and beams.
Many building around the Queenstown CBD will have used this timber.
It is also worth noting both Corsican and contorta pine are a much-sought timber for posts and poles.
I am fully in agreement with the wilding conifer control group and Grant Hensman that invasion into the sub-alpine areas should be controlled, as well as clearing around the few established beech stands still in existence.
I had always maintained this should be achieved through proper management rather than a headlong, expensive attack at huge cost.
More recently, other products have been extracted from conifers, including essential oils and low-emission boiler fuels, such as woodchip.
I repeat: Why not use this resource that cost nothing to establish?
• Jim Childerstone is a semi-retired forester from Hampden.
