Researchers have investigated the impact and productivity of CTL systems when carrying out final felling while retaining the understorey.
The research was titled “Impact and Productivity of Harvesting while Retaining Young Understorey Spruces in Final Cutting of Downy Birch”. The article appeared in Silva Fennica 46 (1), pages 81 to 97. The authors were P Niemisto, H Korpunen, A Lauren, M Salomaki and J Uusitalo. Often Norway spruce (Picea abies) forms an understorey in Birch dominated stands in Finland. Usually, to regenerate Downy birch, Norway spruce is planted after clearfelling. A CTL system (harvester and forwarder) was examined to determine if it was possible to retain the existing spruce trees during harvesting.
The results showed that retaining the undergrowth decreased harvester productivity in managed stands by 6 to 9 %, and in unmanaged stands by 11-17 % compared with clearfelling. With forwarding, productivity of the loading phase decreased by 7 to 14 %. The spruces that were retained had an adequate stand structure for future growing stock. However, 14 to 24 % of the spruces were totally destroyed compared to 25 to 44% when spruces were not purposefully retained as part of harvesting. The research showed that retaining the spruce during harvesting is a feasible option due to no regeneration and tending costs being required for new spruce saplings.
Please access the journal article for a more complete account of the research.
Source: http://www.metla.fi/silvafennica/full/sf46/sf461081.pdf