Steep Slope Harvest System Models for Small to Large Trees

Abstract

Background: Tethered cut-to-length and cable yarding systems with tethered falling equipment are increasingly used to harvest trees from slopes exceeding 30–60% more safely and at reduced financial cost than less mechanized harvest systems. Existing studies of harvest equipment typically isolate one or two pieces of equipment in a harvest system and often occur on sites with slopes below 50% and trees less than 60 cm in diameter. Methods: We analyzed machine capabilities and productivity regressions to extrapolate existing models to steep slope harvesting of trees up to 115 cm diameter. The resulting individual machine models are integrated into models of cut-to-length and long-log harvest system productivity. We estimated the financial operating costs of the harvest systems considered from equipment pricing and operator wages. Results: Analysis of even-age Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla) rotations suggests eight-wheel forwarder productivity, swing yarder productivity, and mechanization of manual chainsaw labor with tethered harvesters as primary controls on harvest costs. Conclusions: The proposed model enables predictions across a greater range of slopes and tree sizes than those previously modeled, creating a foundation for future research into the cost and productivity of steep slope harvesting systems.

Keywords

• productivity and costs of forest operations
• cut-to-length
• winch-assist harvesting
• cable logging
• Douglas-fir
• western hemlock