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NZ’s super-sized weed problem

A new report shows rural landowners are finally waking up to a weed which covers 1.8 million hectares of the country. Their chainsaws are out, but they’re also supportive of “novel approaches” to management.

The invader is not gorse, blackberry or Scotch broom. It’s wilding pines spread by seeds from plantation forests and shelter belts. 

Unlike their well-groomed plantation parents which contribute $5 billion a year to GDP, wilding pines are worthless with harvest often costing more than the wood is worth.

There are 100,000 more hectares of wilding pines than there are of plantation pines and the wind-blown seeds are populating an additional 90,000 hectares a year. Without intervention, wilding pines could cover 20 percent of New Zealand by 2035.

For farmers, wilding pines encroach on grazing land and suck water from pasture. For native flora and fauna, wildings are an invading pest, offering little in the way of food for birds and insects, and dropping an acidic carpet of pine needles which native plants can’t regenerate through.

More than $11 million a year is spent on eradication by land managers, government agencies and community trusts around the country.

" ...  wilding pines are the biggest single threat to biodiversity and the outlook of the high country."

The report from Landcare Research, which is based on survey results, shows a shift in awareness and attitude from landowners as well as support for the breeding of sterile pines.

In the survey report Landcare Research economist Pike Brown says: “The results clearly show that wilding conifers are perceived to be a serious threat and that individual land owners are a key part of a national strategy for managing wilding conifers across New Zealand.”

The report also shows just 2 percent of those surveyed are involved in a national wilding control programme and 54 percent don’t even know it exists. Most landowners are going it alone and removing wilding pines themselves.

A growing awareness

In 2015 just 25 percent of landowners were aware of wilding pines in their region, which has now increased to 60 percent. Attitudes to wildings have changed too. The 2015 survey found 22 percent of landowners surveyed thought wildings were more beneficial than harmful, now just 7 percent think they have any benefit.

South Island respondents were the most aware of the issue.

Federated Farmers North Otago president Simon Williamson said wilding pines were the biggest issue high country faces.

“Rabbits we’ve got on top of since the diseases have come, they were decimating the high country, but wilding pines are the biggest single threat to biodiversity and the outlook of the high country. We’ll end up like Canada if nothing is done while we’ve got the chance.”

Williamson also pointed out another impact. Left unchecked wildings could steal the country’s electricity.

“If they [wilding seedlings] go into trees, in another 10 or 15 years the water loss going down the hydro rivers is equivalent to 53 cumecs, which is a massive cost to the generation industry and New Zealand. It’s probably a quarter of the flow of the Waitaki river.”

The Waitaki hydro station generates enough electricity each year for about 51,000 average New Zealand homes.

"We know the cost of control operations increases if wildings are left to spread so early intervention is the best option."

The majority of landowners surveyed said are controlling wildings on their property, and most with chainsaws. The main reason given was stewardship of the land. Some landowners spend around $40 and a couple of days a year getting rid of wildings. Others reported spending more than 25 days and $10,000 per year on the problem.

According to the participants, the wilding pines come mainly from other properties, with 26 percent blamed on nearby commercial forestry. Eight percent said wildings were from their own forest and 4 percent said wildings were due to historic plantings by the Government.

Despite this, survey results show a shift in attitude to where the responsibility for control lies.

In 2015 more respondents considered controlling wildings should fall to the land owner where the seeds came from. By 2017 more people thought the Government should take over.

The Government’s approach

To date the Government has spent $12.4m, according to Biosecurity Minister Damien O’Conner.

Speaking at the New Zealand Wilding Conifer Group's annual conference, O’Conner said millions of hectares of wildings had been removed by the group.

“We know the cost of control operations increases if wildings are left to spread, so early intervention is the best option. For example, treating light infestations can cost as little as $20 a hectare and dense infestations up to $2000 a hectare.”

The programme is led by the Ministry for Primary Industries and is supported by the Department of Conservation, Land Information New Zealand, NZ Defence Force, NZ Transport Agency. Local government, forestry and farming industries, iwi groups, landowners, researchers and community organisations are also involved. Landcare Research's survey shows 54 percent of respondents had not heard of the programme at all.

The New Zealand Wilding Conifer Group aims to eradicate wildings by 2030 but with the One Billion Trees programme likely to drive the planting of 775 million exotic trees in the next 10 years, there’s the chance new trees will be planted as quickly as wildings are ripped out.

A single mature Douglas fir can produce 20,000 seeds a year and there are no rules around replanting existing forest with the same type of conifer which has been present before.

New forestry rules require new forests and forests which are to be replanted with a different type of conifer to consider the impact of wilding spread. A scoring system looks at indicators ranging from the likelihood grazing cattle will eat seedlings, to how the wind moves around the area to be planted. A high score will require the forester apply for a resource consent before planting can commence.

Landowners are open to another approach, according to the survey report. Scion has been researching breeding sterile trees to end the wilding issue. Fifty-six percent of landowners support sterile trees over current control practices and 43 percent are supportive of using gene-editing technology to achieve this.

Mutant sterile conifers do exist in nature, however, being sterile they don’t breed. Genetic editing, which is similar to genetic modification but does not involve adding DNA from different species could be used to create sterile pines.

In many countries genetic editing is not subject to the same controls genetic modification is, however, in New Zealand any genetically-edited plant would need to be approved by the Environmental Protection Agency under the Hazardous Substances and New Organisms Act before it could be grown outside of containment.

Since this story was published, the Forest Owners Association has responded to queries sent to them yesterday.

A spokesperson said forest owners were also undertaking a range of measures. These included planting buffer trees with a lower seed spread risk, such as pinus attenuata or hybrid radiata around the edge of plantations.

There is also a voluntary good neighbour rule within the wilding conifer strategy which she said responsible corporates were adhering to and some of the worst seed spread species were being eradicated.

“The majority of larger South Island forestry companies are seeking to eradicate Pinus contorta (The most vigorous wilding conifer) from their estates (this is also a requirement of the majority of regional council pest plans).”

There’s research into a spray which might prevent trees from forming seed cones underway and the association also mentioned gene editing of Douglas fir.

“If current legislation was changed to allow this then Douglas fir could become a very desirable high country production species and could also be used as a nurse crop to accelerate the regeneration of understory native species.”

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