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.
Highlights
Models of timber harvest systems are used to support silvicultural decision-making.Silvicultural optimization systems (e.g., [1,2]) rely on harvest system models, along with other models, to guide land management planning
To implement a land management plan, forest harvest contractors need to determine if equipment in the harvest systems they operate is suitable for a given timber sale
Given an understanding of the trees offered in a timber sale and the logs that would be produced from those trees, a harvest cost model predicts each machine’s utilization and the total financial cost for the harvest
Summary
Models of timber harvest systems are used to support silvicultural decision-making. Silvicultural optimization systems (e.g., [1,2]) rely on harvest system models, along with other models, to guide land management planning. To implement a land management plan, forest harvest contractors need to determine if equipment in the harvest systems they operate is suitable for a given timber sale. When a slope is too steep for mechanized harvesting equipment, trees are manually felled using chainsaws [4]. Because mechanization reduces risk to human operators and increases productivity compared to manual felling and bucking [6], commercial winch-assist systems enabled use of feller-bunchers, harvesters, late. The following sections describe the cost and productivity modeling approach used for the three steep slope harvest systems, present harvest cost probability distributions for even-age coast Douglas-fir and western hemlock, and discuss limitations arising from the lack of large tree data and productivity models for some types of equipment The following sections describe the cost and productivity modeling approach used for the three steep slope harvest systems in Figure 1, present harvest cost probability distributions for even-age coast Douglas-fir and western hemlock, and discuss limitations arising from the lack of large tree data and productivity models for some types of equipment
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