Pines being planted in South Marlborough by an Air New Zealand partnership with energy companies are the wrong trees in the wrong place, say biodiversity experts.

Air New Zealand, Contact Energy, Genesis Energy, and Z Energy are partners in Dryland Carbon, which has planted about 10,000 hectares of steep, economically marginal farmland in radiata pine, to offset carbon emissions and harvest timber. This includes at Matiawa, inland from Kēkerengū, and Malvern Hills, in the Avon Valley south of Blenheim, bought in 2020 and 2021 respectively.

”A silly decision made in the name of climate,” is the response of Ket Bradshaw, South Marlborough Landscape Restoration Trust co-ordinator, to the exotic forests being planted in South Marlborough, one of New Zealand’s top five biodiversity hotspots. “Nothing was learnt from disastrous plantings in the 1970s for soil and water conservation.

“When future generations are dealing with wilding spread, they’ll wonder why pines were planted.”

The trust controls wilding conifers, including radiata pine, over 870,000 hectares from south of the Wairau River and the foothills of Blenheim to the Clarence/Waiau-toa and Molesworth/Rangitahi Station.

Wildings could normally be traced back to a nearby forest but up to 20% were found too far away to know their origin, Bradshaw said. Seed rain from both radiata pine and douglas fir – the main forestry and carbon farming species – could fall kilometres away from the seed source.

That meant Dryland Carbon could not effectively control wilding spread along its south Marlborough forest boundaries, Bradshaw said. In this bluffy terrain, poisoning often required hanging from a helicopter, so donating to the trust would be more effective than the partnership attempting to do its own control.

”If we don’t get on top of the spread, the whole of the South Island will be covered in wilding conifers,” Bradshaw warned.

The Matiawa forest adjoined Isolated Hill Scenic Reserve, where there were many rare and threatened plants, and the Malvern Hills forest Ferny Gair Conservation Area.

Rowan Hindmarsh-Walls, Department of Conservation (DOC) South Marlborough ecologist, said: “If there was thick [native]forest everywhere, there wouldn’t be a problem. But there are rocky outcrops and regenerating kānuka and mānuka where there is a high likelihood of pines spreading.”

The Dryland Carbon website said “planting and stabilising steep, erosion-prone country can significantly reduce sedimentation and run-off”. But Hindmarsh-Walls countered that the mudstone soils at Matiawa were not suitable for pines because they were too prone to slumping and slipping.

Earthworks such as building roads and harvesting trees could release masses of sediment into Ben More Stream, which ran through the property, threatening freshwater species such as the northern flathead Galaxiis found only in Te Tauihu/the top of the South Island. Machinery could spread weeds associated with forestry such as buddleia and pampas.

PF Olsen, which managed the Matiawa forest, had accidentally planted pines on publicly-owned marginal strips beside Ben More Stream, due to a fence being incorrectly located. These had been removed, at DOC’s request, Hindmarsh-Walls said.

Dryland Carbon was not anti-conservation and did good work controlling pests on its own properties and in co-operation with DOC, Hindmarsh-Walls acknowledged.

Colin Jacobs, Dryland Carbon executive director, said there was a low risk of pines spreading, which the partnership could manage, based on the Ministry for Primary Industries’ Wilding Tree Risk Calculator results.

But Andrew Macalister, an environmental consultant who managed a programme controlling wilding pines in the Marlborough Sounds, said allowing forest companies to self-assess wilding risk “puts the fox in charge of the hen-house”.

“The Marlborough District Council’s consenting department needs to spend more time working on behalf of the environment and the communities they represent,” Macalister said.

The council should seek biodiversity experts to assess plans to plant forests, he said.

A council spokesperson said there was no way for the council to prevent pines being planted if it disagreed with a wilding risk assessment. Dryland Carbon did not need resource consent to plant radiata pines in Marlborough.

Kaikōura District Council administered the area where Matiawa Forest was planted. Chief executive Will Doughty said staff worked directly with Environment Canterbury to assess the planned forest development under the National Environmental Standards for Plantation Forestry (NES-PF), and both councils agreed it complied.

A Ministry for Primary Industries spokesperson said a council could challenge a wilding risk assessment if it believed a forest did not meet permitted forestry conditions. Councils could also have more stringent rules than the NES-PF, for example, to manage environmental effects on Significant Natural Areas.

A new NES-Commercial Forestry replaced the NES-PF on November 3, tweaking how wilding risk assessments should be done, the ministry spokesperson said.

Jacobs said Dryland Carbon would consider donating to the South Marlborough Restoration Trust towards control of wildings.

“We know not everyone loves forestry but [we] strive to exercise best practice in everything we do.”

No native scrub was sprayed before planting and forests were set back from waterways, Jacobs said. At Matiawa, there were 543ha of established and regenerating native scrublands and forest, and at Malvern Hills there were 350ha including 136ha protected by a QII National Trust covenant.

Dryland Carbon culled about 4000 deer, goats, hares and pigs on the two properties and helped DOC control possums, Jacobs added.

Scott Burnett, Forest & Bird regional conservation manger for Te Tauihu, described Dryland Carbon as “a moneymaking scheme using pines as offsets, which creates many environmental problems”.

“Lifecycle analysis of global plantation forestry shows it emits more than it sequesters,” Burnett said.

More than half of New Zealand pine was exported as raw logs to China, then eventually landfilled and burned.

Burnett said he would prefer to see carbon costs built into air-ticket prices, although this would need government regulation and international agreements.

Overseas Investment Office approval was required for Dryland Carbon to buy Matiawa, but not Malvern Hills, because at that time less than 25% of the partnership was overseas owned.