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NZ needs to plant more trees to combat climate change – but what kind and where?

Sarah Lovell-Smith and Philip King: tangled heaps of pine logs and mounds of silt and debris 10 months after the flood. Photo/Martin Hunter

To counter climate change, New Zealand must vastly increase its area of forestry. But as recent disasters show, not all trees are created equal.

July 2017 had been an unusually wet month on Banks Peninsula, where landowners Philip King and Sarah Lovell-Smith own the historic Loudon farm at the head of Lyttelton Harbour. But on the 21st and 22nd, a storm brought as much rain in two days as normally falls in a month.

Two years earlier, on the steep slopes above Loudon homestead, 300ha of Pinus radiata owned by local forestry investors had been clear-felled. Trees had been harvested up to the edge of Waieke Stream, which flows through the forestry block and the Loudon farm and into the harbour. The forestry contractors had carted the good logs away, and the land was left with the usual post-harvest covering of debris – years of thinnings and prunings, and sawn logs that the contractors had left behind. In the year after harvest, the block had been replanted with a new crop of radiata seedlings.

Macro alias: ModuleRenderer

Sometime before dawn on July 22, the denuded hillside let loose a torrent of mud, felled trees, forest detritus called slash, silt and weeds into Waieke Stream. King and his forestry adviser, Mark Belton, believe the debris formed dams in the stream bed. The water built up until the blockages blew out, sending surges of trees, rock and muddy water downstream through Loudon farm.

The debris flow demolished standing trees in King and Lovell-Smith’s permanent woodlot, dumped thousands of tonnes of logs across their land, destroyed fences, damaged farm tracks and stockyards, scoured out the stream bed, flooded one of the homes on the farm up to the windowsills, and left a thick layer of clay and silt across productive flat land. Even now, 10 months on, Loudon is littered with tangled heaps of pine logs and mounds of silt and debris.

Cyclone Gita ravaged the Nelson area.

King and Lovell-Smith are still paying for the clean-up and repairs – King says the bill is likely to come to $1 million – and they are fighting for accountability. Environment Canterbury, which should have required the forestry company to obtain a resource consent for harvesting but wrongly advised that one wasn’t needed, has decided not to prosecute anyone, despite its investigator’s assessment that the “catastrophic flows” of sediment and logs have damaged aquatic life in the stream and dumped a large volume of sediment, logs and debris into the harbour.

The forest management company, PF Olsen, denies liability and says the flood was triggered by an old slip that was activated by the intense rain. Belton believes the calamity is “entirely” a consequence of the logging operation.

Whatever the outcome of the argument, the disaster at Loudon farm is instructive. New Zealand is on the eve of a new forestry boom. The Government wants to plant a billion trees over the next 10 years. In its draft report on how the country can move to a low-emissions economy, the Productivity Commission says we need to increase the land planted in forests by 1.4-2.8 million hectares. The question is, what trees should be planted, and where?

Forestry adviser Mark Belton.

The prime of pine

The history of tree-planting in New Zealand is overwhelmingly a tale of Pinus radiata, an undemanding and fast-growing species that has been planted in successive waves: in the 1920s and 1930s, when the State Forest Service, as it was then called, realised the country was running out of native wood supplies for domestic requirements; in the 1950s and 1960s, to control erosion; and in the 1990s, by private investors lured by the hope of spectacular returns through special forestry partnerships.

Of this country’s 1.7 million hectares of plantation forestry, 90% is radiata pine, which grows better here than in its native California. It can tolerate our steep hillsides and poor soils, it has outperformed hundreds of other exotic species trialled over the decades and it produces a crop after just 28 years.

Hundreds of thousands of hectares of radiata have been planted in severely erosion-prone regions, such as the East Coast and Tasman districts, to heal marginal land that was previously stripped of its native bush to grow grass for sheep and beef farming. With its rapid growth and large root system, radiata has proved successful at binding the soil on steep country that would otherwise have undergone continuous erosion if left in pasture. Radiata has also done New Zealand a favour from the point of view of our climate-change obligations. Current forestry plantings offset 30% of our gross greenhouse-gas emissions.

But the deluge of logging waste at Loudon farm points to a massive weakness in the country’s plantation forestry system. The so-called “window of vulnerability” is a period of about six years after a radiata crop has been clear-felled, during which the land lies raw, unprotected and at the mercy of rainstorms and cyclones.

In the Motueka Valley, Geoff Miles and Halina Ogonowska-Coates are among several owners of lifestyle blocks in the Tasman district still picking up the pieces after debris flow from a recently felled plantation on the hills behind them crashed through that window of vulnerability and onto their property when Cyclone Gita pounded the country in February.

Damage on Geoff Miles and Halina Ogonowska-Coates’s land in the Tasman district.

Miles says that after a day of steady rain, he heard a loud rumble, then saw a sudden surge of water in the stream that runs through their land. Massive piles of forestry debris caught on bridges and other obstacles upstream prevented more severe damage. But an area that he and Ogonowska-Coates had been restoring to native bush sustained major damage from silt-laden floodwater and smaller forestry slash. Their home, which is on a rise, was not affected.

The forest manager – PF Olsen – cleared the logjams in the stream to alleviate the risk that they would blow and cause catastrophic damage. But Olsen chief executive Peter Clark insisted the company was under no legal obligation to help such property owners; it chose to do so as a “good neighbour”.

Miles says PF Olsen is contributing about $3500 towards the cost of remediation. “It’s something, but in no way covers the huge amount of manpower, expense and emotional stress associated with the clean-up and remediation.”

Much of the forestry in the Tasman region was planted in radiata by the renamed New Zealand Forest Service during the 1960s and 1970s to protect the soil after pastoral farmers had been unable to make a living from the land. Running in a band from Abel Tasman National Park south through the Motueka Valley is a geological feature known as the Separation Point Granites – fragile, steep and erosion-prone country that becomes “extremely mobile” when saturated, according to the Tasman District Council’s principal environmental planner, Steve Markham.

Cutting rights to the former state-owned plantations were sold off to private companies in the 1990s, and much of the flat land in the valleys was subdivided for lifestyle blocks – which, like Miles and Ogonowska-Coates’s property, now lie in the path of debris floods following clear-felling on the hillsides above.

Slips on the Takaka Hill. Photo/Newshub

On the North Island’s East Coast, another region with severely erosion-prone soils where huge areas of native bush were burnt and cleared to make way for pastoral farming, vast swathes of radiata pine have been planted since the 1950s.

Initially they were classed as “conservation” forests, intended to hold the soil and counter the risk of sedimentation and flooding caused by pastoral farming on the steep, deforested country. But according to retired Gisborne Landcare Research scientist Mike Marden, radiata turned out to be such a successful crop that the status of the forests was changed to “production”, and almost all were harvested and replanted in radiata.

These days, the East Coast has 156,000ha of radiata plantations, including trees planted with Government subsidies after Cyclone Bola devastated the region in 1988. Locals, having had the benefit of soil conservation while the trees stood, are increasingly familiar with the window of vulnerability, as huge areas reach the harvest age of around 28 years and are clear-felled. Some of those forests have gone through two harvest cycles, and the post-Bola forests are being harvested for the first time.

According to historian and conservationist Dame Anne Salmond, who is restoring 1100ha of rural land in Gisborne’s Waimata catchment to native forest, the impact of clear-felling is seen in degraded rivers clogged with logging debris and “mountains of slash coming down and landing on pristine beaches”. She says Gisborne port has to be dredged because of the sediment, the cost of damage to bridges and other infrastructure falls on ratepayers and properties are at risk of flooding caused by the build-up of logging debris washed into rivers.

She says that in trying to solve one environmental crisis – the massive clearance of native bush by early farmers – by planting short-rotation plantation radiata, New Zealand has caused another.

Peter Weir.

Rotting roots

The window of vulnerability has been studied in detail by forest scientists. On clear-felled slopes, the roots of Pinus radiata hold the soil for the first year after harvest, but then quickly rot. “Between year two and year six, [harvested slopes] are highly vulnerable,” says Peter Weir, a hydrologist and slope-stability specialist who is president of the Forest Owners Association.

Foresters typically replant a new crop of radiata seedlings within a year of harvest, but Weir says these “do nothing” to hold the soil for the first couple of years. By year three to four, their roots are “getting established, and by year five to six, they are “doing a pretty good job”.

But clear-felling has a second effect on the soil. Weir says about a third of rainfall is intercepted by the canopy of mature forest and evaporates rather than reaching the ground. But clear-fell harvest removes that protection: the soil is wetter and more prone to slips in heavy rain.

“So harvesting triggers a process that, through time, makes the slope more vulnerable if a severe storm comes along.”

On flatter land, the risks are minimal. But huge areas of New Zealand’s radiata pine estate are on steep land. According to the Crown research institute Scion, about a third of our 1.7 million hectares of production forestry is on “erodible steepland terrain” – land which, once cleared by harvest, is liable to shed mud and debris flows during storms.

Around 140,000ha currently in production forest would be regarded as unsuitable for plantation under new environmental standards that came into force this month, according to Oliver Hendrickson, director of spatial, forestry and land management at the Ministry for Primary Industries.

Foresters argue that over the whole life cycle of the forest, the soil conservation virtues of radiata pine far outstrip those of pastoral farming on steep country and that on extremely vulnerable ground like the Separation Point Granites, landslides occur regardless of the type of vegetation cover.

But the fact remains that the business model underpinning radiata pine forestry relies on the economies of scale of clear-fell harvesting, which leaves the land highly vulnerable for up to 20% of the whole rotation period. As Forest and Bird advocacy manager Kevin Hackwell puts it, radiata forest owners “keep their fingers and arms and legs crossed and hope not to get a weather bomb” during the post-harvest window of vulnerability.

But with climate change bringing more intense storms – such as this year’s cyclones Fehi, Gita and Hola – hoping for the best no longer seems a credible risk-management strategy.

Source/Parliamentary Commissioner for the Environment.

Blessing or calamity

As the Government begins to roll out its plan for a billion trees (half of which will be replanted trees on existing forestry land), the question on Salmond’s lips is whether the coming planting boom will be a blessing or a calamity. She has written to Prime Minister Jacinda Ardern to express concern that exotic species such as radiata pine will make up the bulk of the planting and warning that “without good planning” the programme could damage the environment, regional economies and landscapes.

Forestry and Regional Economic Development Minister Shane Jones says he wants the programme to be seen as a “national identity” exercise, but the proposed billion trees are serving many objectives, some of them competing. For starters, there is New Zealand’s carbon liability, estimated by the Ministry for the Environment at $14-32 billion, to meet the gap between expected emissions and our Paris climate pledge to reduce greenhouse gases by 11% (compared with 1990 levels) by 2030. Fast-growing radiata pine is the quickest way of soaking up excess carbon and covering a large chunk of that bill.

Then there is the requirement for forestry-related jobs in the regions – for the “nephews”, as Jones calls them – as well as ambitions for new biofuels and bioenergy sectors using feedstock from an expanded forestry estate.

Jones says he wants the billion trees to include “large swathes of natives”. He has pulled together a ministerial reference group to help oversee the forestry policy, including Environment and Economic Development Minister David Parker, Conservation Minister Eugenie Sage, Climate Change Minister James Shaw and Agriculture Minister Damien O’Connor, which he says will ensure a strong focus on natives. But grants and incentives to induce landowners to plant natives on a large scale have yet to be unveiled.

Meanwhile, forest owners have their own commercial imperatives. They clear-fell about 45,000ha a year of radiata plantations, and need to replant for future cash flow. Mark Belton says the “modus operandi” of the industry is short-rotation radiata crops on cheap, steep land – what he calls “grow and mow”.

Source/Productivity Commission

There is increasing interest in replacing harvested radiata on steep country with Californian redwood, which reduces the risk of post-harvest landslides because the roots graft onto neighbouring trees and sprout new growth rather than rotting. But the availability of seedlings is limited and industry capacity much smaller than in the incumbent radiata sector.

So what’s to stop the coming planting boom repeating the mistakes of the past, which saw indiscriminate planting of “grow-and-mow” forests on fragile land? Julie Collins, head of forestry at the Ministry for Primary Industries, says the objective is to put the “right tree in the right landscape” and MPI is working on a “toolbox” of grants consistent with this goal, which she says will need to be ready by next year’s planting season.

“At the other end, we will be working with regional councils at a more intimate level to say, ‘We have this toolbox, but from a land use planning perspective, where should these trees go?’”

So far, the most significant new scheme rolled out under the billion-trees programme is a major state-funded push to expand the area of commercial radiata pine plantations. A reinvigorated Crown Forestry – the government business unit that oversees forestry assets primarily on state-owned land subject to Treaty of Waitangi claims and on leased Maori land – has been instructed to “jump-start” tree planting by entering into 30-year lease or joint-venture deals with private landowners who have blocks of at least 200ha that have not previously been in plantation.

Collins says the agency hopes to secure 4000ha for new plantings this year and 20,000ha next year – the maximum area that can be stocked, given constraints in the supply of seedlings. Crown Forestry will cover the cost of planting and management; the landowner will receive returns through land rentals or a share of the harvest revenue, or both. The landowner can also earn carbon credits if the forest is entered into the Emissions Trading Scheme.

Julie Collins.

National standards

New National Environmental Standards (NES) for plantation forestry, which came into force on May 1, should reduce the chances that steep, erosion-prone land will be cloaked in new radiata forests. The standards’ new requirements cover harvest planning, the sequence of logging operations, design and layout of tracks and landings, management of run-off during and after harvest and the volume of forestry slash then left on the ground. They also require riparian planting of 5-10 metres, depending on the size of the waterway, to be retained at harvest.

Weir, who was involved in the development of the NES on behalf of the industry, says the game-changer is the development of a detailed map that codes all land as red, orange, yellow or green. Red-zoned land is the steepest and most susceptible to erosion; green is flat, easy country. All planting, earthworks and harvesting on red-zoned land will require a resource consent, which gives councils discretion to set tighter conditions – including the ability to stipulate which species can be planted on land not previously in forestry, and what gets replanted after a radiata block is clear-felled.

MPI’s Collins says the stricter rules mean that trees planted by Crown Forestry as part of its current push to put 24,000ha into radiata will not be on highly vulnerable red-zoned land. But when it comes to radiata plantations that have been recently harvested, regional councils will be in a bind, Weir says: once a crop has been felled, councils will be anxious to protect the soil as quickly as possible – and arguably the best way to achieve that is to plant another crop of radiata, which locks up the soil in about six years, compared with a species like Douglas fir, which takes 10 years, or natives, which take longer still. But a new generation of radiata merely buys another 25 years of soil stability before the window of vulnerability is opened up yet again at the next harvest.

Redwoods, with their durable root system, are seen as a possible contender to replace existing radiata forests after harvest. But although new seedlings put down roots and stabilise a site as quickly as radiata, they are less site-tolerant and are unlikely to thrive in colder, drier South Island conditions.

Oliver Hendrickson.

The need to break out of this dependence on short-rotation radiata pine crops on steep erodible sites is on the minds of officials at MPI. Hendrickson says the challenge is to “transition some of this land out of pine and into permanent forest cover. But we need to work with the landowners around that. They have invested in the land, and they have an investment model around that.”

Belton, who specialises in permanent carbon forests, is concerned the billion-trees programme could lean too much towards the commercial forestry industry’s short-rotation harvesting model. Instead, he says, New Zealand should be planting permanent mixed-species exotic forests, which protect the environment and permanently lock up climate-damaging carbon.

Such an approach doesn’t need government subsidies, he says; it just needs reasonably priced land and a rising carbon price that trades within a predictable band. He says a price range of $20-$30 a tonne is enough to make carbon farming commercially attractive, provided it is on low-value land types. “No one would advocate putting these forests on good agricultural land. They should be planted on land that should never have been cleared in the first place. We shouldn’t be just doing massive industrial forestry expansion; we should be looking at how to integrate trees into the landscape, with commercial forestry on easier land and long-run carbon, soil-conservation and biodiversity-enhancing forests on other land.”

But Salmond finds the idea of planting permanent exotic forests on land that should never have been cleared of its native trees abhorrent. In the tussle between exotics and indigenous species, the ability of natives to quickly recolonise and protect vulnerable land has been underestimated, she says: on her Gisborne land, livestock were removed and the foothills planted in native trees. Kererū and other birds spread the seeds of those trees up the steeper slopes, which have reforested “extremely quickly. We had a closed canopy in 11 years – very rapid regeneration.”

Source/Parliamentary Commissioner for the Environment

The missing vision

As competing interests scramble to promote their preferred version for the coming planting boom, perhaps the piece that’s missing is an intergenerational vision for our forests. Andrew McEwen, a former president of the New Zealand Institute of Forestry, says he’s pleased that forestry is again seen as a legitimate concern of government. “But there is a strong need for governments to have good advice within their own bailiwick, rather than relying on all the pressure groups – the carbon foresters, the farm foresters, the big industry guys.”

He and other forestry professionals are pushing the case for a long-term forest policy that covers “all forests, all species, and all tenures”.

“If you go to many other countries this is what other governments have – because forests provide more benefits to society and to the economy, environment and culture than any other land use.

“If we have stable soils, if we have carbon being taken up furiously by trees, if people can go and recreate in forests and tourists can enjoy looking at them, those are benefits for all of society, and so all those interests need to be protected.”

This article was first published in the May 12, 2018 issue of the New Zealand Listener.