Saving lives in our forests

UC research is helping to reduce the number of injuries and fatalities that have historically occurred from treefelling activities on steep slopes.

  • Rien Visser and Hunter Harrill

    Dr Hunter Harrill (left) and Associate Professor Rien Visser.

Researchers are helping the Aotearoa New Zealand forest industry develop cable-assist harvesting systems. Associate Professor Rien Visser and Dr Hunter Harrill of the UC School of Forestry have built strong industry relationships with a number of commercial forest companies since 2008, when cable-assist harvesting first began in Aotearoa New Zealand.

Associate Professor Visser says Aotearoa New Zealand has had a relatively high fatality rate in the forest industry, in the last decade averaging five or six deaths a year, primarily forest workers with chainsaws felling trees on steep slopes.

“Machines that can cut down and process trees have been around for a long time, and putting operators inside these machines is a much safer option than a worker on a slope with a chainsaw.

“But these machines are restricted in where they can operate. Steep or soft ground impedes their movement and can compromise safety. There is always potential for them to lose traction or even tip over, so we need to be careful we don’t just replace one hazard with another. This is where our research comes in.”

While cable-assist harvesting was first proposed in Europe 25 years ago, it has only been practised in Aotearoa New Zealand for ten years, initially introduced by Ross Wood, a highly innovative contractor from Nelson. His prototype system Saving lives in our forests was a bulldozer at the top of a slope with a wire rope (cable) attached to a machine felling trees below.

Taking a new approach

Associate Professor Visser explains how things are much more sophisticated now.

“We use a second ‘anchor’ machine stabilised on the top of a slope, with an integrated winch and cable that assists movement of the machine working on the slope below. This greatly extends the range of operation and reduces risks to the working machines.”

It is the operating limits associated with this system that Associate Professor Visser and Dr Harill’s forest engineering research focuses on, especially testing cable tension and slope limits and feeding these back into the industry to continually improve safety margins. This research has received sustained funding from an industry and government consortium called Future Forest Research.

“These are large machines we are talking about. Basically, we have 40 tonnes of machinery being held on a cable, so it’s important to understand the loading and strain on that cable, and how that loading changes as the machines move up and down the slope through different gradients and surfaces,” Associate Professor Visser says.

Unexpected opportunity

These systems are not only saving lives in our forest industry, but they have also created an unexpected opportunity for Aotearoa New Zealand to step into manufacturing these machines, he says. There are now four companies producing 20 to 30 machines between them annually, with many being sold overseas, particularly to Canada.

“Canada has a larger industry, and much of their forested terrain is also very steep. Because they also have a strong focus on health and safety, they not only want to purchase these systems, they also want to know how to best manage them as well.

“So we hold workshops in Canada, as well as here in Aotearoa New Zealand. These are attended by three particular groups and the workshops that work best have a good representation from all three.

“First are the machine operators themselves, secondly the contractors who buy the machines and manage the systems, and finally company representatives who do the harvest planning, decide which contractor goes where in the forest, and when the systems can be used or when they can’t.

“We recently had a software engineering student, Amy Martin, work with us to develop a tension monitoring app that we also demonstrate at the workshops. It displays how the cable is interacting with the winch visually, in a similar way to a heart-rate monitor. That app is now being commercially developed by a manufacturer in Nelson.”

Associate Professor Visser says this is a real boon to operators, especially when they strike a problem and are concentrating completely on controlling the machine. The app stores data from the event for review later, providing a really useful feedback mechanism for constant improvement.

During their visits to Canada and different regions of Aotearoa New Zealand, Associate Professor Visser and Dr Harrill actively promote cable-assist systems as a safer alternative to manual felling with chainsaws.

“We are talking about a big investment and new challenges. A forest worker with a chainsaw is basically a $2,000 tree-felling system. This alternative averages around $1.3 million because you need two large purpose-built machines. There’s a big difference, and while it works faster, it’s more expensive per tree cut and requires improved planning,” Associate Professor Visser says.

“However, when such costs are required to be safe, the industry has been very responsive in accepting that to ensure we end up with higher standards that protect our workforce.”