The spraying of Douglas fir wildings near the Roaring
Meg power station in the Kawarau Gorge earlier this year has
reignited the debate over the control these trees. Today, Peter
Willsman argues why they have to be removed.
Wilding pines are colonising bluffs above Queenstown.
High up on a tussock face a volunteer, Jack, is cutting
Douglas fir and larch wildings.
''How did all these wilding trees get up here?'''
'It's the wind,'' Sid replies. Jack looks around him.
''But the nearest conifer trees are at least 4km down the
''And that,'' says Sid, ''is the challenge of wilding
''Wilding'' is the term used for unintended regeneration of
conifer species that seed and spread. Most people appreciate
trees. I certainly do. A stately pine, a magnificent Douglas
fir, the autumn colour of a larch tree; each one is a
wonderful example of the wider conifer species.
Unfortunately, particularly downwind, these same conifers can
release vast quantities of seeds which germinate and quickly
grow, smothering our alpine lands.
There are helpful ways of understanding wilding control.
Planting the right trees in the right places is one way
forward. Conifers, whether in forest blocks, smaller planted
areas, or specimen trees, enhance our landscapes, offer
shelter and can offer commercial value.
The choice of site and species is important. It is time now
to think about Douglas fir, larch, Scots or Corsican pine
trees and windbreaks on an exposed sites that are within a
few kilometres of high country or on land that is not heavily
The pioneers and settlers planted conifers without realising
how they would spread. Unfortunately, poorly sited conifer
woodlots, windbreaks, have spread and will continue to take
over vast tracts of high country unless they are halted.
In a perfect world, wilding conifers would not need to be
felled, cut or sprayed but prevailing wind and strong wind
events scatter the seed for kilometres. Pinus contorta has
spread from the faces of Mid Dome in Southland. Young
contorta tree weeds are now showing up in the alpine lands
near Waikaia. The Mid Dome Trust is investing hundreds of
thousands of dollars in an attempt to eradicate these tree
Near vulnerable alpine lands, some landowners are replacing
their conifer shelter belts with non-seeding trees such
eucalypts, thuya, poplars, abies - a Spanish fir - and
Understanding the potential seed spread from the various
conifer species is helpful.
Pinus radiata, the large-limbed pine trees whose cones we
love for lighting the fire, produce heavy seed which is only
released on hot days and falls close to the parent tree.
Douglas fir cones hang on the end of branch tips. They can be
laden with cones which open in the autumn and release large
quantities of light seed. This seed can be blown anywhere
from metres to kilometres, depending on the wind event. In
the Wakatipu area Douglas fir seeds are blowing up from lower
land and establishing high on the craggy bluffs of the
Larch, green in spring and gold in autumn, makes delightful
specimen trees in gardens, in parks and away from alpine
lands. Larch seed is also light. Windblown, it germinates,
grows rapidly and produces seeding cones.
Contorta pine seeds profusely and can be windblown
(''distances of up to 40km are possible in very strong
winds'', Ledgard NJ, 2001), although most seeds drop and
germinate within shorter distances. The time between seed
germination and the new tree coning and spreading varies with
The time factor between seed germination and a conifer coning
affects the wilding threat. Radiata pine takes about 15 years
to cone and is a low threat, whereas Douglas fir not only
seeds and germinates profusely but it can also, with good
conditions start coning in under 10 years.
Douglas fir is a major problem in the Wakatipu area. Contorta
pines begin producing seeding cones within six years and must
be removed by landowners under the ORC pest management
legislation. Eradicating and controlling wildings before they
take over much of Otago's high country requires understanding
the dynamics of the species and their potential invasion.
A few old pines will spread very slowly and are very low
risk. Removing high-risk seeding trees as soon as possible is
a top priority. Leave profuse seeding Douglas firs on or near
vulnerable land and the cost of containment escalates out of
control. Cutting and spraying conifers is costly and not
Leave the trees now and they will spread rapidly up to 1100m
and over into the next valleys. Nationwide management
strategies on wildings adopt the mantra of ''a stitch in time
saves nine''. An area of wildings might cost $100,000 this
year to control; if left for five years $500,0000 will be
Rational, though not always popular, decisions can be made if
weed tree control is understood. If left or ignored, the cost
of leaving coning wildings will become too great. A contract
gang of six men costs $1800 per day plus helicopter
transport. On heavily infested rough high country, the area
cleared each day is small. At more than $2000 per hour,
spraying dense wilding areas by helicopter is more cost
effective and regrowth is minimal.
No method is cheap. Trusts, councils and landowners will not
continue to pour finance into going over the same alpine
lands controlling these weeds while seed from wilding blocks,
such as at Roaring Meg, blows down Kawarau Gorge and up on to
Rational, well-communicated decisions will be to remove
seeding conifers where possible, to plant and appreciate good
specimen trees that enhance our landscapes. Thoughtfully
chosen ''right trees in the right places'' offers the way
Peter Willsman is chairman of the Wakatipu Wilding Conifer