Simulating conventional and integrated stump- and round-wood harvesting systems: a comparison of productivity and costs

Tree stumps could make a significant contribution as a renewable energy source in the transition away from reliance on fossil fuels. However, ground disturbance due to stump harvesting can be an unintended negative environmental consequence. Harvesting only the central part of the stump can reduce ground disturbance, but this is not profitable with the machinery and systems currently used. One possible solution is to integrate the harvesting of stump-center and round-wood in a single operation. We compare an integrated system for such simultaneous harvesting of stems and stump-centers with a conventional system harvesting stem and stump separately. The conventional system used a harvester, a forwarder, a stump harvester and a stump forwarder, while the integrated system used a feller-puller that fells the trees with the stump center attached, an in-stand processor, and a forwarder. The work of the machines was simulated using discrete-event simulation and the costs of the two machine systems were compared. The integrated system produced only 12–33% of the stump-wood volume produced by the conventional system. The integrated system produced stump-wood at a lower cost than the conventional system for larger trees (>420 mm breast-height diameter). For smaller trees, it was not possible to determine which was the more economical system. Further empirical data are required to resolve the issue, for instance concerning the time required to cut or break the roots around a tree.