Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

New Technology Helps Control ‘Wilding’ Pines

Spraying wilding trees with a specially designed gun.

Spraying wilding trees with a specially designed gun.

Recent advances in wilding tree control allow operators to work from the air, which is more cost effective and efficient than dropping off crew at individual trees.

“The new technology reduces the need to deliver staff, armed with chainsaws, by helicopter to control individual outlying trees in remote areas,” says Stefan Gous from Scion, who has played a key role in developing the new techniques.

The term ‘wilding trees’ generally refers to conifers that regenerate naturally, spreading into grassland or shrubland. Many of these species were actively planted for erosion control in the past. The most common method of spread is from exposed take-off sites, where the prevailing winds allow seed to be blown into nearby habitat. The main culprits are lodgepole or contorta pine (Pinus contorta), Corsican pine (P. nigra), European larch (Larix decidua) and Douglas fir (Pseudotsuga menziesii). Many of these species were actively planted for erosion control in the past.

Wilding conifers are a problem primarily in the Marlborough Sounds, the South Island high country and the central plateau of the North Island, but are also invading natural habitats in Otago and the Mackenzie Basin. Because these trees grow in dense stands, and are not able to be managed as a plantation would be, they have no economic value. Instead, wildings reduce the value of managed pasture, displace native biodiversity and alter the character of the landscape. The impacts of wildings on productive land and on conservation values are well documented but control programmes present a number of challenges. As well as the sheer scale of the problem some of the areas affected by wildings are remote and difficult to access, making it a dangerous and costly exercise to reach them.

As with other invasive species in New Zealand, pines have a competitive advantage here. In their native range, pines are pioneer species and are efficient colonisers but have insect seed predators that have a big effect on seed viability. In contrast, New Zealand has few bark borers, wood borers or seed predators adapted to living on Pinus, which is partly why the forest industry is so successful. Biological control was considered at a workshop attended by affected stakeholders in 2003, and the availability of some highly specific seed-feeding potential control agents was noted. However, it was also clear that there were a lot of questions about the potential safety and usefulness of biocontrol agents. In particular concern was expressed that if the serious disease, known as pine pitch canker (Fusarium circinatum), was ever accidentally introduced to New Zealand biocontrol agents might exacerbate the situation by spreading it around. Along with the feeling that the battle could still be won with existing tools (subject to sufficient funding and skilled operators) biocontrol was not pursued further, and instead efforts went into improving existing tools.

The new technology developed by Scion has involved developing a suitable cocktail of herbicides that have good penetration, uptake by the plants and mortality rates. “A combination of triclopyr and paraffin oil has been tested and is showing great results,” says Stefan. Up to 85% mortality has been seen in trees treated this way. Another advantage of this herbicide is that it can be applied outside of the growing season of the pines. The key to applying it is in the specially designed gun with a 1.5-m wand that can be operated from within a helicopter. The wand enables operators to spray the crown of the tree thus minimising the effects on surrounding vegetation. By eliminating the need to fell the trees, there is no physical disturbance to the surrounding vegetation, therefore reducing the chances of secondary weeds moving in such as gorse or broom. “The Department of Conservation is already using the new spraying system with success and expect there will be a significant reduction in operating costs as a result,” confirmed Stefan.

This project is funded by the Ministry of Business, Innovation and Employment as part of Landcare Research’s Beating Weeds Programme.

Stefan Gous