By Tess Brunton of RNZ
The lead investigator of a nationwide fight against wilding pines says they can't stop work to eradicate wildings or risk the tide turning against them.
Before 2016, wildings were estimated to be invading roughly 90,000 hectares each year.
Later that year, a five-year government-funded research programme, Winning Against Wildings, was launched aiming to control or contain wildings nationally by 2030.
It has sparked new knowledge, research and techniques for controlling the pests including remote-sensing tools to detect and map invasions in remote areas and using low-dose herbicides to control dense wilding invasions.
Wildings were thought to occur on at least 1.8 million hectares nationwide.
But without control, estimates suggested they could invade 28 per cent of the total land area within 35 years.
The programme's principal investigator Dr Duane Peltzer said this collaborative research meant they were better set up to control wilding pines, particularly in difficult, dense and remote terrain.
"They do have distinct spectral or reflectance so that's using remote sensing you can find them so that's one possibility. You can use flyover, fixed wings - this is largely Scion has run this - around automated mapping so that's trying to plan operations, through to some of the social and economic work we've done."
There was not one technique that worked everywhere.
"The terrain and remoteness add hugely to the cost so just the excess, the moving from A to B or having to use a combination of ground crews, helicopters and other approaches mean the costs do go up in those complex remote areas."
He said good progress had been made to control wilding pines but more work was needed.
"The hardest thing with weeds is if you stop you actually lose the game so the things that we're really concerned about next is the reinvasion.
"There's no one off finishing the job, you actually need to go back a second and third time, and it's also about what do we want from that land use longer-term?
"There might be other things aside from removing conifers that we need to do and so certainly there's ongoing needs for beyond just controlling or containing wildings. What do we want next?"
This all started when they were facing an uphill battle against the pest back in 2016.
"At that stage, we thought we were losing the fight against wildings."
That was where the programme hoped to step in, using science and collaboration to understand how they could do better and how they could turn the tide against wilding pines.
Five years later and there was better knowledge and improved techniques for controlling them as a result of the programme.
"Part of the motivation for the whole programme was looking across the whole invasion curve and we're probably really aware of this with Covid and squashing the curve.
"So that was the idea is that there is no one tool that controls wildings at the early, mid or late stages of invasion and so in the early stages, it's things like backpack spraying, cutting. It's really hard to find individual trees in the landscape so that's where things like the remote sensing and mapping were really important."
There had been huge improvements on finding the early stages which was the most efficient time to do the management, he said.
The research had managed to quantify the spread risk among wilding confider species, uncovering that their dispersal distance was further than previously known.
Dr Duane Peltzer said the spread risk was also driven by variation in seeds within individual trees rather than there being a few risky trees that were the main cause of an invasion.
Public awareness was on the rise - in part following the devastating Lake Ōhau fire last year - with more people recognising them as a problem.
The evidence, knowledge and research would go towards business cases for further work to contain and eliminate wilding pines.
In particular, there was an investment case planned to go to the government next year.