High log-processing costs are making many stands in central British Columbia uneconomic to harvest, especially those with small-volume trees that are heavily impacted by the mountain pine beetle epidemic. Previous work showed that multi-stem processing with a stroke delimber could reduce processing costs, but produced lower-quality sawlogs that severely impacted sawmill production. Alternative methods for multi-stem processing that generate sawlogs of acceptable quality need to be developed.
The Quadstar 500 dangle-head processor from Southstar Equipment Ltd is a new to processor in British Columbia designed for multi-stem processing. Its productivity and quality performance relative to conventional single-stem processing method was evaluated in a stand of small, dead pine west of Quesnel, BC. The trials also evaluated the cost and benefit of using a modified log specification and processing technique intended to reduce the amount of in-woods processing, and instead deliver more non-sawlog fibre to a central yard where it could be removed. The modified sort specification was to cut stems to a pulp-log diameter limit instead of a stud-log length limit. The modified sort specifications were used for both the Quadstar processor and an older stroke delimber.
Multi-stem processing with modified sort specifications increased productivity by approximately 4 m3/PMH and reduced processing costs by approximately $2/m3 compared to the conventional single-stem processing. Several factors contributed to the productivity increase, including more fibre utilization and the nature of multi-stem processing itself. The modified log specifications resulted in more volume being produced from the available stems with less roadside residues, and more cycles where a log was produced. Although the multi-stem processor was slower than the conventional processor when processing just a single stem, its time per stem was less when it processed two stems simultaneously.
The log quality in the dimension sawlogs was approximately equal for multi- and single-stem processing. However, the multi-stem processing with the modified sort specification generated 50% less roadside residue than the conventional log specification. Subsequently, the pulp sort that was delivered to the mill, and that normally contained less than 1% waste, had 19% of its volume in a form that was unsuitable for stud logs. Since the pulp sort comprised 40% of the volume in the modified sort specification, about 8% more fibre was delivered to the mill and was suitable only for pulp or biomass.
Multi-stem processing using the stroke delimber with modified sort specification shows promise because of its higher productivity, however, the trial was conducted with old equipment and additional validation with modern equipment is required.