Economic feasibility of an integrated harvesting system for small-diameter trees in southwest Idaho

Mechanical thinning in dense, small-diameter stands is being increasingly considered to reduce the risk of wildfire in the Interior Northwest of the United States. Economic feasibility of small wood thinning and utilization is in question due to the low market value of thinning materials and high costs for thinning and transportation. Two cost models were used to estimate thinning costs for various harvesting systems. Tree volume and potential product recovery (roundwood, clean chip, and biomass fuel) were computed and used to analyze the economic feasibility of small wood thinning and transportation in southwest Idaho. Harvesting costs for small-diameter trees increased with decrease of tree size, especially with skyline and helicopter systems. At average 10-inch diameter at breast height (DBH), skyline and helicopter stump-to-truck logging and chipping costs were about three and six times more expensive, respectively, compared with a mechanized whole-tree harvesting system that showed the lowest cost at $34.23/100 ft. ³. A sawlog harvest only option with a mechanical whole-tree harvesting system showed a positive return ($/acre) when hauling distances were less than 53 miles. Other harvest options that included clean chip and/or biomass fuel as well as sawlogs were not financially viable, indicating that transportation of low market value materials (clean chip and biomass fuel) resulted in more cost than revenue. The factors affecting economic feasibility of small wood harvesting include forest harvesting systems used, road accessibility and conditions, hauling distance to manufacturing facilities, and market price of thinning materials.