Hoffmann Stephan, PhD

Background: Small-scale forests (woodlots) increasingly account for a greater proportion of the total annual harvest in New Zealand. There is limited information on the extent of infrastructure required to harvest a woodlot; road density (trafficable with log trucks), landing size, or the average harvest area that each landing typically services.

Methods: This study quantified woodlot infrastructure averages and evaluated influencing factors. Using publicly available aerial imagery, roads and landings were mapped for a sample of 96 woodlots distributed across the country. Factors such as total harvest area, average terrain slope, length/width ratio, boundary complexity and extraction method were recorded and investigated for correlations.

Results: The average road density was 25 m/ha, landing size was 3000 m2 and each landing was serviced on average 12.8 ha. Notably, 15 of the 96 woodlots had no internal infrastructure, with the harvest completed using roads and landings located outside of the woodlot boundary. Factors influencing road density were woodlot length/width ratio, average terrain slope and boundary complexity. Landing size was influenced by average terrain slope, woodlot length/width ratio, and woodlot area.

Conclusion: The results provide a contemporary benchmark of the current infrastructure requirements when harvesting a small-scale forests in New Zealand. These may be used at a high level to infer the total annual infrastructure investment in New Zealand’s woodlot estate and also project infrastructure requirements over the foreseeable future.

Traction assistance of forest machines via traction aid winches has gained widespread application in steep-terrain forest operations as it can mitigate soil disturbance by reducing wheel or track slip of the assisted machine. Since slip affects machine operations in flat terrain as well, especially on fine-grained and moist soils, the effectiveness of traction assistance under such conditions was evaluated. At a forest site, a forwarder with a total mass of 28.6 t was driven over two plots in 15 passes. The machine travelled unassisted over one plot, while on the second plot traction assistance was manually adjusted to keep slip close to 0%. Wheel slip and winch tractive force were recorded during each pass, and rut depth was measured after each pass. Soil density was measured pre-impact and at three times after different traffic increments. Although the mean wheel slip was low even during unassisted travel, traction assistance was found to cause a significant reduction. While both a decrease in rut depth and soil compaction were observed with traction assistance, only the latter was significant after three machine passes. A potential influence of inhomogeneous soil reinforcement due to roots suggests repeating the experiment on a more homogenous soil.