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New Zealand has plenty of trees – but do we have enough?

October 08, 2020

Most of this article originally appeared on Stuff.

There was a time when we planted a lot of trees, but then, all of a sudden, we stopped.

That needs to change quickly if New Zealand plans to meet its climate change targets.  Failing to plant billions of trees over the coming decades would be an expensive mistake and may require us to meet the shortfall for any excess carbon dioxide (CO2) we’ve failed to offset, likely by buying costly international carbon credits.

It’s easier said than done. Planting trees is a unique policy challenge, despite the fact that nearly everyone agrees that it’s a good thing to do.  The benefits of planting trees are both uncontroversial and extensive. Trees limit nutrients getting into waterways, and when planted on erodible land, they stop mud slipping into rivers and lakes.

In its recent report on limiting global heating to less than 1.5C above pre-industrial levels, the Intergovernmental Panel on Climate Change (IPCC) outlined several ways to get there.  Nearly all of them involved some degree of “negative emissions”. That means we can’t just stop adding CO2 to the atmosphere, we need to start taking it out, too. Far into the future, new technology may make that possible on a wider scale.

For now, we only have one reliable way to do it, albeit for only temporary periods: Planting trees.

It sounds easy, but there are a lot of complicating factors, particularly in New Zealand, which has a landscape well suited for trees but a human population that excels at cutting them down, not so much at planting them. Whether we do or don’t meet our climate change commitments depends largely on this question: How much CO2 can we store in trees by the time our carbon bill falls due?

New Zealand has a lot of trees, but far fewer than it used to.

Around one third of the country is forested, compared to around 80 per cent prior to human colonisation. Much of that forest is on the South Island’s West Coast, in the form of mature native trees. But when it comes to climate change, time is not on our side. Under the Paris agreement, New Zealand needs to meet an emissions reduction target by 2030. This 2030 target will be challenging. It requires greenhouse gas emissions to be 30 per cent lower than 2005 levels. The maths is complicated, but based on recent projections, New Zealand is on track to go around 200Mt of greenhouse gases over budget, nearly three years worth of emissions. Meeting that agreement will need a combination of three things: Reducing emissions, offsetting emissions with trees, and buying international carbon units.

In its lengthy report on a low-emissions economy, the New Zealand Productivity Commission concluded the amount of forested land would need to increase between 1.3m to 2.8m hectares by 2050 to reach net zero emissions.

This is a lot of land. It amounts to between five to 10 per cent of New Zealand’s total land area.  This would require planting between 44,000 and 90,000ha of new forest every year for the next three decades, a rate only achieved once, for a brief period in the mid-1990s. It’s a massive escalation of recent efforts: For much of the 2010s, New Zealand mostly gave up on planting trees.

The commission proposed a solution: Most of this land could come from marginal sheep and beef farms, which would benefit from native trees. This would have the dual benefit of taking methane-producing animals off the land and replacing them with CO2 absorbing trees.

Many farmers have already shown a willingness to increase the biodiversity on their land. Native bush helps with water quality and erosion, among other things.

In a lot of cases, you don’t even need to plant native forest – simply fencing off land and controlling weeds and pests can allow native bush to regenerate on its own.

It does, however, mean giving up land that could be economically used.

The commission said to make this sort of planting happen, the carbon price will need to go up. When the carbon price is high, allowing trees to grow on your land could become lucrative. Instead of farming animals, you would be farming carbon itself.

At the moment, the carbon price is around NZ$35 per unit; this would need to go up to as much as NZ$250 by 2050 to make the necessary amount of planting happen. Whether the government is willing to allow the price to go this high will be a factor in how much forest is planted.

We desperately need trees, and that requires planting them. But it comes with risks.

Some rural groups have raised concerns about the impact of forestry on rural communities.

If farms become forests, it will change the fabric of the place; animal farming provides jobs, and circulates money through rural communities. Using the land to passively grow trees would change that.

On the flipside, not planting enough trees will mean New Zealand has to meet its climate change commitments by either rapidly decarbonising the economy, including the industries we most rely on, or buying international carbon credits to cover our shortfall, which by 2050 could cost many billions of dollars.

You can read the Productivity Commission Report here