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Doctoral thesis, 2018

Improved harvesting technology for thinning of small diameter stands : impact on forest management and national supply of forest biomass

Sängstuvall, Lars


Forest biomass is used as feedstock for forest products as well as for bioenergy. The current Swedish roundwood utilization is near the sustainable maximum. This implies that increased forest biomass consumption in Sweden must utilize additional parts of the trees already harvested, and/or that small trees not utilized today must be harvested, with current or novel methods, techniques and practices. This thesis explores thinning of small diameter forest stands with the removal of thinned trees including stems, tops, branches and needles – biomass thinning (BT) in Sweden. Major advances in BT were witnessed in the Nordic countries between the years 2005-2010. Harvesting in a geometrical pattern (boom-corridors), with a conventional harvester head or a specialized area-based felling device, was defined and conceptually evaluated. These evaluations showed potential BT harvester productivity gains, but the lack of generic productivity models for BT machines prevented further analyses. The overall objective of this thesis is to analyse the impact of such new BT harvesting technology with regards to recovery costs, forest management and national forest biomass supply. Many of the scenarios analysed in this thesis include non-existing phenomena, a fact being one of the challenges for providing reliable BT assessments. A harvester simulation model was used to quantify BT harvester productivity benefits from geometrical harvest patterns and area-based felling devices. Deductive modelling boosted the conclusions that could be drawn from a limited and heterogeneous set of empirical observations on BT haulage with medium-sized forwarders. Derived generic BT harvester and forwarder productivity functions were implemented in the Heureka decision support system and thus available in the subsequent SweFor partial equilibrium model, which was examined for influences of assumptions regarding land owner behaviour and saw log supply models. Finally, SweFor was employed to quantify the forest impact, and national potential supply, of forest biomass from BT. Given the current energy market conditions, BT was the preferred management regime on about 15% of the managed Swedish forest area, and provided 15% of the total supply to heat plants. Market limitations aside, BT could increase with more than 300%, which could be seen as a potential for increased forest biomass utilization for other products. In conclusion, this thesis demonstrates methods to address forest operations and management research questions including non-existing phenomena, and confirms BT as a viable major future option in Swedish forestry.


thinning, biomass, harvester, forwarder, simulation, deductive framework, forest planning, forest impact, sector model, partial equilibrium model

Published in

Acta Universitatis Agriculturae Sueciae
2018, number: 2018:66
ISBN: 978-91-7760-272-9, eISBN: 978-91-7760-273-6
Publisher: Department of Forest Resource Management, Swedish University of Agricultural Sciences