News and stories

Keen student takes on the challenge to spot wilding pines from space


30 October 2018

Drive around the beautiful wide landscapes of the Mackenzie Country and you’re bound to spot some wilding pines.

Because they mature early and produce a large number of relatively small seeds, wilding pines have invaded an estimated 1.8 million hectares across New Zealand, ranging from tussock grasslands and high-country farmland to native forests.

Rowan Sprague - a student on a mission

Bio-Protection Research Centre PhD student Rowan Sprague is working on a way to find wilding pine trees in remote areas by using image data collected from satellites and aeroplanes. Known as remote-sensing data, this is a rapidly developing technology and could be a low-cost way to find remote trees, especially in grasslands.

Rowan has written a detection algorithm that lets a computer automatically process the image data and detect where the pines are.

It hasn’t all been plain sailing. After trying several software programmes and methods, Rowan wrote her own algorithm. It took her several months to get the algorithm to specifically detect wilding pines, and not other trees. It was also tricky getting it to estimate the number of trees in a dense stand. The fun part was then getting out into the field to see how well it worked!

“When I compared what the computer could detect with what I found and measured in the field, I found that the resolution of imagery affects how accurate the results are. But it does appear to find all adult trees,” Rowan says.

“While the method isn’t perfect – and it’d be nearly impossible to get it to detect very small seedlings – it adds another tool to more easily and effectively find where the wilding pines are establishing.”

“By doing so, we’ll be able to control the spread of these trees and save our beautiful indigenous and productive grasslands.”

Rowan’s method will ensure all bases are covered

New Zealand spends millions of dollars each year trying to remove these trees. Te Uru Rākau – Forestry New Zealand alone funds a large project to control them, costing $16 million a year. This project involves regional councils such as Environment Canterbury, Land Information New Zealand (LINZ), the Department of Conservation, and landowners.

The work being undertaken by Rowan is helping to overcome one of the major obstacles to successfully controlling wilding pines, knowing exactly where they are. We can see those near major highways or on easily accessible farmland, but what about those spreading to isolated parts of the high country?

To find and control trees in isolated areas, staff from DOC, regional council, and other control organisations fly around in helicopters on search-and-destroy missions, or rely on previous knowledge of where the pine trees were. This can be time-consuming and expensive, and there’s risk that if they miss trees, they’ll continue to grow. Rowan’s work will give them assurance that they’ve got all bases covered.