CWG observations from controlled burn targeting Wilding Pines

Written 26^th September 2025 by CWG project manager, Pete Oswald.

Dense young pine infestation being burnt in a controlled burn.

See video of the burn below text.

Summary of Main Points:

• A landowner farmer in Central Otago has used fire to controlling wilding pines.

• We, the CWG, have been assisting this landowner with controlling wilding pines since 2016.

• The burn operation was a collaboration with a neighbouring commercial forest, other neighbouring farmers and CWG.

• Scion group, Bioeconomy Science Institute are researching the effectiveness of this fire through measuring equipment deployed in the burn area by CWG and pre and post fire observations by Scion staff.

• CWG also recorded detailed imagery of the fire.

• Immediate indication is that the trial has been successful.

• If it is as successful as early assessments indicate, this has greatly progressed CWG’s control program in this area towards protection of the surrounding land including over 50,000 hectares of conservation land.

• CWG, in partnership with Scion and MPI, will monitor the situation over time to determine the success or otherwise of this project.

• It is indicated that fire will be a useful tool for controlling wildings in very specific circumstances where the right burning conditions can be achieved, the fire can be safely contained and investment in follow up control/land development can be carried out to prevent reinvasion. These requirements may mean it is not the cheapest option for a lot of areas.

Further Detail:

On the Thursday the 25^th of September the CWG was invited by a landowner to observe a controlled burn of wilding pines in Central Otago. Our project manager and 1 board member was on site.

The burn was planned and managed by the landowner and supported by the local community of farmers. A local forestry company also supported the planning, management and execution of the burn. This group of people is very experienced and skilled in effective and controlled burning practices.

Scion group, Bioeconomy Science Institute, a Crown Research Institute for forestry in New Zealand, gained permission from the farmer through the CWG to record data from the burn. We offered to deploy measuring devices for Scion before the burn and retrieve them after the burn when their staff were unable to come to site. We also recorded imagery of the burn. Recording of data and imagery was done successfully and with the permission of the landowner. We did not engage with the execution, planning or strategy of the burn. We only observed the controlled burn. However, we have been working with the landowner to assist with a land use strategy that would mitigate future infestation on this specific area of land.

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. 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.

We concluded this apparent success was due to an accumulation and alignment of conditions and circumstances that may be very difficult to replicate. These conditions and circumstances included:

·       Tree size, density and consistency.

·       Abundant other fuel – tall ungrazed grasses.

·       Ideal fuel and weather conditions leading up to, the day of and after the burn.

·       Considerable time investment and very long-term planning from the landowner.

·       Wealth of experience, knowledge and support from the local community.

·       The landscape and features of the burn area such as existing and natural fire breaks.

·       Past pine control work of the surrounding the area.

Approx. 1 hour after the burn.

The conifers were small and consistent in size ranging from approx. 0.2 metres up to approx. 4 metres in height. They were very dense; in many areas they were closed canopy cover even though they were small trees. Where they were not closed canopy, they were fairly dense. The other vegetation onsite was mainly abundant grasses - many tall tussocks. This had not been grazed by livestock for over 18 months, so there was abundant tall fuel other than the wilding conifers.

Due to past wilding pine control work over the past decade around the burn site, the pine infestation was largely confined to the burn area. There were also natural fire breaks surrounding a lot of the burn area including farm tracks, an airstrip, and short green grass. The landowner had also added an extra turned earth fire break days before the burn.

The farmer had been trying for 3 burn seasons (over 18 months) to do this burn but had not struck the right conditions until now. This window of conducive weather was identified about 2 weeks out. The necessary people were put on standby for a possible burn day several times but then stood down again because conditions were not quite right. On the burn day the ignition was delayed approx. 2 hours until conditions were just right.

There were considerable costs involved including a helicopter with monsoon bucket on standby onsite. Approx. 12 people we on site managing and executing the burn.

The burn is just one step of many to control this wilding conifer infestation. Follow up work after the burn to mitigate regrowth and re-infestation will take considerable expense over a long period of time.

The main origin seed source of the infestation is widely believed to be from the neighbouring commercial forest. That forest is continuing to improve operations to mitigate seed spread and maintains wilding control to a 200m radius around the forest on the neighbouring land. CWG has spent considerable resources since 2014 containing this further spread on the surrounding landscapes, which is now largely confined to areas close to the seed source.

One of our main objectives is protecting a vast area of land around this site from aggressive wilding conifer spread, including over 50,000 hectares of vulnerable conservation land.

See also this interview on Radio New Zealand National with Scion group, Bioeconomy Science Institute about the burn: https://www.rnz.co.nz/national/programmes/ninetonoon/audio/2019006381/scientists-explore-new-way-to-rid-land-of-wilding-pines