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New Zealand is highly regarded internationally for its forest health, import quarantine and pest eradication systems. But with rapidly increasing human traffic and international cargo volumes have caused an increase in the number of biosecurity breaches by unwanted pests and diseases.
| The Resources At Risk (2004 Figures): |
| State and private indigenous |
6.21 million ha |
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| Plantation forests |
1.82 million ha |
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| Value of all forest product exports |
$3.3 billion |
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| Employment in forestry |
23,000 |
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Control of Pests and Diseases
New Zealand forests have been largely free from serious attacks by insects and disease. With so much of the plantation forests in radiata pine, there is a monoculture crop. Concerns have been expressed by biologists about the wisdom of creating monocultural forests as they may be prone to attack by disease; in which case there is a risk they will be seriously damaged or completely wiped out. This is in contrast to mixed species forest plantations. In a mixed forest, if disease or insect pest strike it would only destroy certain species of the trees and the remainder would be free of attack.
The New Zealand forest industry has balanced the risks involved and concluded that radiata pine culture is justified because of its superior performance and because many of the criticisms do not stand up to scientific evaluation. There are extensive natural forests of single species (monoculture) throughout the world, e.g.:
• Beech forest in New Zealand;
• Douglas fir forest in North America;
• Spruce and fir forests of Europe and Russia.
Natural and plantation forests are surveyed regularly in New Zealand for signs of disease or animal and insect attack. All forests aerially surveyed on an annual basis for signs of tree damage. If an area is sighted with possible problems, the area is investigated further by ground surveys.
Dothistroma needle blight, a fungus which attacks the needles of several pine species, was a major concern in the forests in the 1970s. This fungus is now readily controlled by using copper sprays.
The wood wasp Sirex attacks the trunks of trees. The wasp lays its eggs into the tree wood at the same time releasing a mucus and a fungus into the wood. After the eggs hatch, the larvae tunnel through the tree which has also been infected by the fungus. The larvae pupate inside the tree and the adult wasps chew their way out of the tree. The Sirex wasp has been successfully controlled by the introduction of a parasite which destroys the wasp larvae and is a successful example of biological control of a pest.
More recently, the painted apple moth – a serious threat to native bush - was found in Auckland in 1999 and an extensive spraying programme during 2003 controlled, if not eliminated the problem. Only one moth has been trapped since May 2003. Swift, co-ordinated government response to the problem, following a biosecurity alert, was shown to be very effective.
Pitch canker is potentially lethal fungus to New Zealand's radiata and other pine species. It has caused enormous damage in the United States and should it penetrate New Zealand's biosecurity screen, there would be little hope of halting its progress.
For further information see Biosecurity Briefing.
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