Two multi-tree harvesting systems were compared with a single-tree system in first thinning of scots pine.
The authors were Jani Lehtimaki and Juha Nurmi of the Finnish Forest Research Institute (Metla). The paper is titled “Energy wood harvesting productivity of three harvesting methods in first thinning of scots pine (Pinus sylvestris L.)” and was published in Biomass and Bioenergy 35 (2011) pp 3383-3388. An OM-Waratah 745 single grip harvesting head mounted onto a Timberjack 870 harvester was used for felling and processing, and a Timberjack 1110 forwarder for extraction.
The single-tree harvesting (STH) consisted of conventional single-tree harvesting where the pulpwood was delimbed and the top (undelimbed) removed. The two resultant assortments were left as stacks along the extraction route. The first multi-tree harvesting (MTH) system processed one to four trees simultaneously. The pulpwood and the tops were delimbed. Both assortments were bunched along the extraction route, with the residue remaining scattered along the extraction route. The second MTH system carried out all processing at the stump immediately after felling, aiming to leave residues spread throughout the compartment. Pulpwood and energy wood sections were delimbed and processed using MTH.
The results showed that the two MTH systems increased harvester productivity by 28 to 35% over the STH system. The greatest reductions in work cycle times occurred in the felling and delimbing elements. Forwarder productivity was lower using MTH system 2 due to longer loading times for the different assortments and a lower mass of material per grapple load. This system however left residues better distributed across the site.
For a more complete account of the research, please access the journal at http://www.elsevier.com/locate/biombioe