Could forestry’s unwanted wood become the road beneath the logging trucks? Deals on Wheels went to find out.
There is normally little shortage of wood in a New Zealand plantation. The problem is that not all of it is worth putting on a truck.
After the merchantable trees have been extracted, forests can be left with a mixture of branches, stems, offcuts and other woody material. Getting that residue out of the forest can be expensive, while leaving large piles behind creates its own problems, particularly when heavy rain gets involved.
Now, a trial in Hawke’s Bay is turning that leftover material into something the forestry industry needs almost as much as it needs timber – roads.
Forest Growers Research, working with Pan Pac Forest Products and operations technical co-ordinator Hamish Scown, has been trialling shredded forestry residues as a temporary roading aggregate. Three test roads were constructed with shredded wood approximately 500mm deep and then subjected to the sort of treatment that tends to expose any weakness in a forest road, which is loaded logging trucks.
Funding for the project is from the Forest Growers Levy Trust and the Ministry for Primary Industries.
The results so far have been surprisingly encouraging.
One of the trial roads at Joule Road in the Mohaka Bridge Block handled approximately 5000 tonnes of stems, carried by 18-metre stem trucks weighing up to 50 tonnes GCW. Initially, the loose shredded material had traction problems on steeper sections, but traffic compaction – or compaction using a roller – quickly improved matters.
In fact, according to the information gathered, most of the compaction occurred during the first 20 vehicle passes, after which the surface became progressively more stable and stiffer.
That is significant because conventional forest roads generally depend heavily on quarried or naturally occurring aggregate, which can be expensive to extract and transport, particularly when the forest is some distance from a suitable source.
The shredded-wood approach turns that equation around. Instead of bringing large quantities of aggregate into the forest, some of the material already sitting there can be processed and put straight back to work after being processed with a suitable wood chipping machine.
It also offers another potential advantage. Unlike a conventional metalled surface, the wood is permeable, allowing water to move through the road rather than simply running across its surface. FGR says this can reduce sedimentation and runoff and make rehabilitation easier and cheaper, particularly during winter.
But this isn’t a case of simply throwing a load of wood chips onto a track and sending the trucks down it. The material needs to be prepared and placed correctly. The trials have been examining different particle sizes and construction techniques, while compaction has proved particularly important.
The trial also found that adding conventional aggregate can improve performance where traction becomes an issue. Both 65mm and 100mm crushed aggregate were tested, with the larger material performing better. The aggregate effectively works its way into the shredded wood, producing a denser, more interlocked surface.
The approach has its limits, though. Wet, steep grades remain a challenge, and the road design needs to minimise mud being carried onto the wood surface. Providing sufficient running distance on flatter ground before a steeper section proved useful during the trials.
The origins of the idea can be traced back to the clean-up following Cyclone Gabrielle, when shredded wood was used to provide firm footing for machinery working on wet silt. That experience demonstrated that the material could do considerably more than simply sit in a pile waiting for someone to decide what to do with it.
In February 2025, about 50 forestry engineering, harvesting and environmental representatives visited the Pan Pac trial in Mohaka Forest. The concept subsequently attracted interest from other forest management companies around the country.
The next stage is to work out precisely where the system works best. FGR’s Phase Two trials are looking at roller compaction, different shred depths and the possible use of geotextiles to improve drainage. The eventual aim is to establish practical specifications, application methods and approximate costs for the industry.
There is a certain irony in the idea. Forestry spends considerable money moving material into forests to build roads, while simultaneously spending money dealing with material it doesn’t want.
The Pan Pac trials suggest that, in the right circumstances, one problem might provide the answer to the other. The forest waste doesn’t have to leave the forest. It might just need to become the road.
In August, Hamish won the award for Best Young Presenter for this work at the Low Volume Roads 2026 Workshop in Hamilton, which was hosted by the Road Engineering Association of Asia and Australasia.
For more information, contact Hamish on +64 27 878 4630 or Hamish.Scown@panpac.co.nz.
Images supplied
