sing brush mats with forwarders - how much do they really help?

The increasing use of logging residues for energy production reduces the amount of slash available for the forwarder to travel on. This article looks at how much brush is necessary to protect the soil.

Logging residues used for biofuels need to be free from as much mineral soil as possible. If the forwarder travels over the residue, the residue can be contaminated. However, if it travels directly over the ground it could compact the soil. To determine how much residue was necessary to protect the soil, trials were carried out whereby a 2000 Timbco TF820-D forwarder travelled repeatedly over varying amounts of logging residue generated from balsam fir and black spruce. The eight-wheeled forwarder had a tare mass of 23,5 tonnes and a load capacity of 20 tonnes. Two Olofsfors band tracks weighing 1,100 kg each (2,400 lb) were installed on the rear bogies.

Increasing the number of loaded passes from 2 to 12 caused the brush mats to lose some of their ability to distribute loads, but still provided an acceptable level of protection. When no brush mat was used, the forwarder exceeded the 150 kPa threshold 97% of the time, compared to only 41% of the time when the forwarder travelled over the 30 kg/m2 brush mat. As expected, the load distributing ability of the brush mat increased as the brush mat thickness increased. Previous studies have shown that leaving greater than 10 kg/m2 of brush was sufficient to reduce the wheel loads of an eight-wheeled forwarder. This study recommended leaving 15 to 20 kg/m2 on sensitive sites and as much as possible on sections of the extraction route that are very sensitive. Therefore, any remaining slash could be used for biomass purposes.

This research was published in the Croatian Journal of Forest Engineering, Vol. 33 (2012) 2. The authors were E Labelle and D Jaeger. Source: http://crojfe.sumfak.hr/download/dwnld_33-2.html