Productivity and costs of utilizing small-diameter stems in a biomass-only harvest

Abstract

The expanded use of woody biomass for energy has increased the number of in-woods chipping operations across the southeastern US. Young loblolly pine (Pinus taeda) stands that undergo a first commercial thinning, or sometimes a pre-commercial thinning, may serve as a potential raw material source for these chipping operations. A harvesting case study was completed using activity sampling and elemental time studies to analyze conventional logging equipment thinning and chipping of a 15-year-old planted loblolly pine stand located in the coastal plain of Virginia. All stems in the harvest were chipped for biomass and no pulpwood or sawtimber was produced. Overall individual machine productivity rates for the feller-bunchers, skidders, and chipper were 27.9, 21.2, and 75.9 green tonnes (gt) per productive machine hour, respectively. A total cut-and-haul cost of $21.28/gt was calculated using the Auburn Harvesting Analyzer (AHA). Hauling was found to comprise the largest component of total costs at 33% or $6.30/gt. Conducting sensitivity analyses by balancing the operation in the AHA reduced the cut-and-haul cost by 5% to $20.21/gt. Considering a regional average delivered price of $15.74/gt for in-woods whole-tree pine biomass chips, the operation in the case study failed to break even. Results of this study suggest that current delivered in-woods pine chip prices are exceeded by harvesting costs in biomass-only harvests of young pine stands; however, optimally balancing operations will improve feasibility.