Stakeholders are waiting to see how effective a 50-hectare fire lit on a Central Otago farm has been in controlling invasive wilding pines long term.

Initial reports are hopeful the trial will show controlled burns can be added to the toolkit for tackling the spread of the weed.

The burn, carried out last Thursday, was instigated by the landowner - a Central Otago farmer keen to target wilding pines on their property.

Central Otago Wilding Conifer Control Group project manager Pete Oswald observed the operation, supporting research underway by scientists from Scion, a Crown research institute working under the New Zealand Institute for Bioeconomy Science by setting up some vital kit on the ground prior to the burn beginning, to record information on it.

“The fire appeared to be largely successful in that it burnt exactly to plan and to a good intensity where it was needed to but always stayed in control and within the planned area,” Pete said in a report on the event.

“The efficacy also appeared to be successful, however, the true success of the fire in terms of kill rate of pines and mitigation of seed germination will not be known until the next growing season, and maybe as long as 24 months after.”

Scion fire ecologist Shana Gross told RNZ’s Nine to Noon show on Tuesday (September 30) the trial was a strong example of collaboration to combat the plant pest.

Her team will use data collected before, during and after the burn on factors such as tree diameter, fuel moisture, fire intensity, weather conditions, how high the flames reached in the trees, and how much green foliage remained after the blaze to inform their ongoing research.

“We really are looking for those thresholds to better understand what we can kill with what kind of fire,” she said.

Approximately one hour after the burn. Image: Central Otago Wilding Conifer Control Group

The plan is for her team to revisit the site over summer to assess “what sprouts back”, but at this stage Shana considers fire most effective for controlling younger trees.

National policymakers are also following the trial. Biosecurity minister Andrew Hoggard issued a statement on Tuesday describing wilding pines as invasive weeds that overrun both farmland and conservation areas.

He said he had directed Biosecurity New Zealand to look at “all practical options” for controlling the species and was cautiously optimistic about controlled burns as one such tool.

“The objective is for the controlled burn to get hot enough and last long enough to destroy the cones on the trees and any wilding seed already in the soil. If successful, this will reduce the need, and cost of future control efforts,” he said.

“However, it is a complicated undertaking. It can only be done in the right conditions, and with careful measures in place to keep people and the environment safe.”

During the Central Otago trial, a fire safety plan and fire breaks were in place, with a firefighting helicopter and trained personnel on site.

Central Otago Wilding Conifer Control Group captured drone footage and photographs of the burn, which have been published on the group’s Facebook page.

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