Cable-assisted (or tethered) mechanized harvesting has recently been introduced to the Pacific Northwest of the United States, and is rapidly being adopted by the forest industry. However, potential environmental impacts, productivity and cost of the new harvesting systems have not been well-assessed. This study aims to examine the effects of cable assistance on soil compaction, system productivity and cost through a field-based experiment. A harvester-forwarder system was used to thin a harvest unit on dry soils in western Oregon, with and without cable-assistance. We conducted a detailed time study during operations and collected soil measurements before and after machine passes. Machine productivity ranged from 28.75 to 92.36 m3 per scheduled machine hour, with resulting unit costs for untethered and tethered systems ranging from $13.19 to $18.13/m3. Our results showed reduced soil impacts in both extent and degree of soil compaction when cable assistance was employed. The reduced extent of soil impacts is attributed to a reduction in track wander owing to the operative tensions of the tether cable, and the smaller increase in soil density appears to be attributed to combined effects of initially denser soil conditions and reduced shear displacement as a result of cable-assistance.

The increasing use of cable-assisted steep-slope harvesting has presented different operational, safety, and environmental opportunities and challenges. One of the primary benefits is the increased safety introduced when tethered equipment is used appropriately—notably, “appropriate” use is the use of cable tension for assistance, not stability. However, the stability of such equipment on realistic soils under wet or dry conditions is not well defined, blurring the transition between tethering as a safety measure or as an aid for traction. Therefore, we propose an approach that enables assessment of the stability and required tensions to ensure stable equipment operation under various configurations on steep slopes. A sensitivity analysis was performed, including two equipment track geometric parameters: track width and grouser depth, and soil properties by evaluating two distinctive soil types. Equipment geometry had a role in stability, but less than the influence of soil shear strength. For equipment properties, grouser depth presented the greatest effect on stability, concentrated between slopes of 36–70 percent. Greater soil moisture increases equipment stability in sandy loams and significantly decreases stability in clay loams. When the effects of soil properties are isolated, cohesion and angle of friction are the properties with the greatest effect on equipment stability.

Numerous researchers have worked on measuring and predicting wood moisture content to increase wood's economic value for bioenergy production. Most have focused on small logs, and predicting models include methods such as heuristic fitting and multiple regression. Finite element analysis (FEA) is a method that allows determining drying rates while offering the flexibility of changing the way these residues are stored and their shape and location, material properties, and drying seasons. FEA was used to develop drying rates for four different Oregon climate regions including Willamette Valley (Douglas-fir), higher elevation Douglas-fir, Coast (Western hemlock), and East (Ponderosa pine). Compared with field data, statistical tests show model agreement with correlations between 0.56 and 0.92 in all sites. After performing analyses, we can conclude that selection of pile shape or size can be beneficial or detrimental toward drying, depending on ambient conditions. Windrow is the shape that mostly promotes drying in the summer and rewetting in winter. It is best to reduce pile size to facilitate drying in summer and increase pile size if material will be left in the field during winter. Drying times can be reduced by one-third if the material is cut and left drying during summer versus winter months.

Winch-assist or tethered logging technology is rapidly being adopted by the forest industry across the western United States to replace conventional and dangerous manual tree falling in cable logging areas. Although the safety benefits of the technology are widely acknowledged, the effects of tethered mechanized timber falling and pre-bunching on the subsequent cable yarding operations have not been thoroughly investigated. We conducted a field study in southern Oregon to compare manual versus mechanized timber falling side-by-side for their impacts on the productivity and costs of cable logging operations. Our study shows that the costs of mechanized timber falling were higher than manual falling owing to high costs of tether equipment, but the ability of the felling machine to pre-bunch trees into piles along designated skyline corridors made subsequent cable yarding operations significantly more efficient. The efficiency gained during yarding was sufficient not only to offset cost increase in felling but also to reduce the total production costs of felling and yarding operations by 32% compared with cable yarding after manual timber falling.

Moisture content management is key to improve forest harvest residue economics for biofuel production. Branches are a large component of these residues, especially when residual bole components are diverted to pulpwood. The literature is not clear about seasonal moisture patterns for the main forest species commercially harvested in Oregon, and most studies have focused on bole wood. A repeated-measurements experiment was implemented to determine seasonal moisture content changes in four western and central Oregon research sites. From all sites, the highest moisture recorded was 50% in ponderosa pine during winter; the lowest was 43% in the summer for Willamette Valley Douglas-fir. Ponderosa pine had significantly higher moisture content in the winter compared to other seasons (1.6–9.0% higher), and summer branch moisture was considerably lower than fall (4.4–2.0% lower). Willamette Valley Douglas-fir branches had significantly lower moisture content during summer compared to other seasons (1.0–4.8% lower). In addition, regression equations were developed to predict branch moisture content from branch height (R² 0.36–0.58) and branch heartwood diameter (R² 0.69–0.93). Although branch heartwood resulted in a more accurate alternative for predicting branch moisture content, it requires destructive sampling.