What is it?
The radiata pine is a stalwart of New Zealand's forestry industry, because conditions here are so favourable to its growth. This same factor is responsible for the nuisance factor of `wilding pines', the name given to pine tree species when they spring up uninvited.
Wilding pines in the Wakatipu area
Pinus radiata was introduced to New Zealand before 1860. It grows in only a few small areas of its native California but is widespread in New Zealand. It will grow on sand, withstand a certain amount of salt spray, and even several degrees of frost won't harm it. So it flourishes from coastal areas to high altitudes. It needs only 600 mm of rain a year, which means it can grow almost anywhere in New Zealand. Other pine species which create a nuisance as wilding pines include Pinus contorta and the Douglas Fir.
Why are wilding pines a problem?
Pines seed very efficiently from pine cones. The wind-blown seeds are widely distributed and need no nurturing to take root.
Wilding pines are a nuisance in areas where native forest does not occur, such as above the bushline, in mineral belts and tussock grasslands. In areas such as these it creates a major intrusion and modification to natural ecosystems.
In areas where native forest regrowth is being encouraged pines are visually intrusive.
They compete for forest space with native trees and plants, but provide none of the advantages these offer, such as berries and nectar, to encourage bird life and insects. Pine needles form a carpet which discourages regeneration of native forest floor species.
Methods of control
Aerial wilding pine control by helicopter
Manual Control: Most pine species will not regrow if they are cut down, provided all branches and needle formation below the cut are cleaned off the stump. If this is done carefully the use of herbicide is not required. In the Marlborough Sounds, cutting wilding pines down rather than ring-barking is preferred for aesthetic as well as practical reasons. If ring-barking is used it is important to ensure the trees, when they finally fall, will not cause a hazard to electricity lines.
Hand-weeding is labour intensive but suitable for areas of low infestation. Small wilding pines can be pulled or eased out of the ground with a tool. Shake the soil from the pine's roots and place any available leaf litter over the site where the pine has been pulled. Don't leave bare soil as this will encourage further pine seeds to germinate.
Ring-barking is an alternative to using herbicides on trees with a sufficiently large trunk. With a sharp chisel, axe or chainsaw make two deep parallel cuts into the sapwood right around the base of the plant. Vigorous ring-barking is recommended for pines. Cuts should be no less than five centimetres apart and all the bark should be removed from between the cuts.
This method is not always successful as a callous may grow to heal the wound, or the plant may resprout from the base.
Details about the various methods of herbicide control are available from the New Zealand Wilding Conifer Management Group website. As with all herbicide use, you should read the instructions on the manufacturer's label closely, and always wear protective clothing.
Contact any Department of Conservation office for further information on the identification and control of invasive weed species. District Councils also have pest control officers who will be able to advise you on control methods.
A useful reference book is `Native Forest Restoration: A Practical Guide for Landowners' by Tim Porteous (Queen Elizabeth the Second National Trust, 1993).
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