We’ve been hearing a lot about tethered logging systems at Trout Mountain Forestry, so we decided it was time to check out an operation. Brent Klumph, Timber Manager for Oregon State University’s forest management program was kind enough to invite us out for a tour of an active harvest that is utilizing this type of technology on OSU’s McDonald Dunn Forest outside of Corvallis.
Tethered logging systems are not new, having been utilized in New Zealand on the steep (and similar) terrain there. The systems themselves aren’t utilizing any dramatically new technology either. In tethered systems, a winch has been fitted to the back of a piece of equipment such as a harvester or a forwarder. The winch then allows that piece of equipment to access 40%+ slopes by tying itself off to an anchor point and lowering itself down or climbing up a hillside. If a slope “breaks away” in a different direction from the original descent line, the operator would then anchor off to a 2nd anchor point to be able to lower themselves down the new slope’s fall line.
Like a more traditional ground-based harvest, protection of skid trails and corridors from compaction remains a potential concern and can even be amplified on steeper slopes. Depending upon the time of year and the type of logging (whole tree vs. cut-to-length for example), there may not be enough slash available to place in the corridors for the machines to travel upon.
Economics are a big consideration, of course, especially in thinning work. The stand must be at a certain age and condition to make the harvest viable, and these systems aren’t cheap. That said, the ability to thin on steep ground had been limited to more conventional cable thinning in the past, which comes with its own set of constraints (logging crew size needed, increased exposure for the ground crew, associated cost of a larger crew, etc.). When OSU ran the numbers on the harvest that we visited, they found that they were saving money over using a cable thinning operation, and actually had better utilization of their wood. Due to the added flexibility and maneuverability of the tethered logging system, they were even able to retain more trees than they would have through a cable thinning.
A big drawback right now is that there is currently only one operator with this type of equipment in the state. Although that operator has thirteen “sides” (thirteen harvester/forester combos), they are in high demand and are difficult to schedule less than a few years out, especially during fire season. This could perhaps change if other operators decide to invest in this style of equipment. Though tethered logging systems may not be a silver bullet for steep slope harvesting, we do see the potential for this technology to expand our management options in rugged terrain. In that sense, it is exciting to have another “arrow in the quiver” to help us accomplish our clients’ forest management objectives.