There is a general consensus that New Zealand needs more trees. The new Government understands this; why else would they have set a target of a billion extra trees over the next decade?

It's a worthy aspiration. But a policy it is not, just a targeted figure.

We need to be cautious. Impulsiveness is a characteristic of the tree-lover, which can easily lead to mistakes, the rectification of which takes time and can be costly. So this undertaking demands much consideration, and counsel from those experienced in matching trees to the environmental landscape, and their care and management from planting to maturity.

Most definitely the wishes and needs of those who own and manage the land expected to be planted must be heard, for it will largely be on private land where planting will need to happen.

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Most of the debate to date seems to be whether the plantings should be pines or natives, the latter being more sexy. What about all the other species on offer and in many cases more practical and beneficial than radiata or natives?

It is true radiata forestry comes with social and environmental baggage, a burden it doesn't deserve. Yes, it displays a monotonous landscape and harvest is a traumatic exercise on steep land, though such land may still be best suited to forestry.

Further, because of its long rotation (long by the seasonal cycle of the land use it replaced, though not by global forestry practice) its ownership tends to change from a residential family structure to corporate, often foreign, ownership.

But the pine industry deserves a better image. I suggest that plantation radiata, which seriously began in the 1920s, mainly in the centre of the North Island, has done more to save our indigenous forests than any political or environmental movement.

This was the result of one of the most unheralded technological innovations in our history — the commercial application of pressure treatment with tanalith, introduced in 1952. This made a naturally non-durable timber suitable for external and in-ground use.

Thenceforth we had a home-grown economic substitute for our native timber. Of course native harvesting didn't end overnight, but it wound down over the next few decades.

Today New Zealand's native forests are effectively under total legal protection from exploitation and, bar minute amounts of specialty imports, all our timber needs are met from plantations of exotic species, over 90 per cent of which are radiata.

Name another country that can claim this. Globally only 10 per cent of timber is from plantations. Environmentalists should hail our radiata pine industry.

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On the other hand though, exotic trees are threatening our naturally regenerating bush through wilding invasion, and our picturesque tussock landscapes too. Included in the species is radiata pine, and that is why I have been careful to qualify the tree's merits as a plantation species.

This is an ecological degradation that has received insufficient attention for too long. In consequence, much regenerating bush is doomed.

Over the past 20 years or so I have written of my concerns to three conservation ministers. The results are pretty well consistent, "Thanks for your letter. We share your concerns. We can assure you that we have an eradication strategy in place to address this problem."

It is my view that seeking to arrest this advancing frontier should take precedence over a programme of wide-scale native tree establishment. Yes, it is a daunting challenge but then, so is the establishment of native forest from grassland.

The phrase "plant more natives" slides off the tongue like a greasy sausage off a hot plate. My impression is the most vocal advocates haven't tried it. The planting alone can be expensive, given the cost of the individual tree and the numbers needed to establish a bush-type association.

But that is just the start. The on-going aftercare is likely to be a challenge that will never sleep. There is the control of competing vegetation in the early stages, and thereafter of invasive exotic weeds, and not just trees. Blackberry will surely appear, carried within the gut of birds, and other weeds just too numerous to mention.

It is true that many natives are being planted, as the huge upsurge in native plant nurseries over the past 20 or so years confirms. So there are many examples of bush creation, such as pockets on life-style blocks, farmland and public reserves.

But they are small and manageable. To expect farmers to embark on wide-scale native bush establishment, well, why should they? The land must pay its way.

Carbon credits help but are insufficient to prompt conversion. If they were, it would already be happening.

There are numerous alternatives to pine or natives that excite interest, especially with promotion and demonstration. They involve a wide range of exotics planted at wider spacings and with grazing after initial establishment, which allows for easy access, greater weed control, reduced fire hazard, and the income from livestock, as well as the possible eventual harvest.

Such plantings enrich our productive rural landscape.

Trees are intergenerational gifts. We should avoid a rush into this afforestation programme, and measure the options. What's a year or two in developing thoughtful strategies?

• Ewan McGregor is a farm forester and holder of several forestry and environmental awards. He is a former deputy chairman of the Hawke's Bay Regional Council.