An examination of the current slope gradients being experienced by ground-based forest machines in New Zealand plantation forests.

摘要

Harvesting is typically one of the largest cost components within a plantation forest rotation. A large proportion of New Zealand’s future harvest will be on steep terrain. Currently steep terrain harvesting is characterised by lower productivity and higher cost. It also has higher levels of manual or motor manual tasks such as setting chokers or tree felling, with a corresponding higher safety risk. The utilisation of ground-based machines on steep terrain has the potential to decrease harvest costs and improve safety. There is currently a push in New Zealand to increase the operating range. This is being done with a poor understanding of the slopes on which machines are currently operating and little understanding of the new risks steeper slopes might introduce. To better understand the true range of slopes on which forest machines are operating, a digital accelerometer was attached to 22 forest machines and provided real-time measurements of slope. The evaluated machines were grouped into one of four machine types; felling (n=4), shovelling (n=5), skidder (n=9) or European (n=4). The machine types were then analysed with respect to their machine slope (actual) and terrain slope (predicted) based on a digital terrain map. Two methods of calculating terrain slope were used, method one was based on a triangular irregular network (TIN) file with method two based off a raster file. Linear regression indicated that there was a relationship between machine slope and terrain slope for all four machine types, with the exception of European based machines, using the TIN method of slope calculation. All variables showed a poor coefficient of determination with the highest adjusted R squared single variable explaining 17% of the variation. All machines operated on slopes that exceed the New Zealand approved code of practice guideline of 30% and 40% slope for wheeled and tracked machines respectively. New Zealand based machines were shown to exceed the guidelines for terrain slope much more frequently, and by a greater margin, than European based machines.