Thursday, June 7, 2012

Methodology for choice of harvesting system for energy wood from early thinning

Dissertation by Juha Laitila


The primary aim of the present study was to develop  a methodology for estimating procurement cost of forest chips from early thinnings. The methodology employs time consumption functions, productivity parameters and cost factors of various phases  of the sub-operations (e.g. management, cutting, forwarding, chipping, transporting) included in the production systems. The wood procurement cost data was linked with worksite conditions and wood availability in order to obtain reliable information for choosing harvesting method for energy wood procurement from young stands. The most common logging systems and supply chains of forest chips used in early thinnings in Finland were compared at stand and regional level using productivity models and cost parameters obtained mainly from the sub-studies of this thesis. Furthermore, a decision tree was constructed for selecting an economically, ecologically and socially sustainable harvesting method for energy wood originating from early thinnings.
Forwarding productivity following mechanised cutting was significantly higher compared to productivity after motor-manual cutting. Mechanised cutting by the harvester enables felling and bunching of whole trees into large grapple loads close strip roads, which facilitate increasing forwarding output and cost reduction. The two-machine system composing of a harvester and a forwarder was the most cost-efficient logging system due to efficient cutting, and especially forwarding phase. The cost of motor-manual whole-tree cutting was equal to mechanized whole-tree cutting, while forwarding cost after motor-manual cutting was almost double that after mechanized cutting. Using a forwarder based harwarder resulted in highest logging costs. However, with  large tree volumes and removals its costs were almost equal to those of motor-manual based logging. A  breakthrough of the harwarder system requires cost reduction by improving  machine technology, as well the working techniques.
Available volumes and procurement costs of fuel chips made of small-diameter trees were compared at regional level. The trees were harvested either by multi-stem delimbed shortwood or whole tree method and chipped by truck mounted drum chipper at the roadside landing. In the shortwood method, the trees were delimbed as bunches by a conventional harvester head equipped with multi-tree-handling (MTH) accessories. The calculation was made for a hypothetical plant located in Central Finland, and the radius of the procurement area limited at 100 km via existing road network. Based on the availability analysis, delimbing reduced regional cutting recovery by 42% compared to whole tree harvesting, when the minimum accumulation of energy wood was set at 25 m³/ha. Delimbing reduced the recovery rate of biomass, and thereby also the number of potential harvesting sites with an adequate removal was reduced. However, the study showed that forest energy potential can be increased and procurement costs reduced applying shortwood method with multi-stem delimbing in stands stands where whole tree harvesting is not recommended because of potential nutrient losses or  other ecological reasons. Using versatile machinery in thinnings increases the flexibility of forest operations and thereby improves cost-efficiency.
When selecting the decision criteria for the decision tree, the interests of the stakeholders involved in the forest chip production process, i.e. the wood-harvesting entrepreneur, the wood procurement organisation, the machine operators, the forest owners, the chip consumer, and the community, were taken into account. The decision criteria in the decision tree were as follows: Harvesting Costs at the Roadside Storage, Minimisation of the Harmful Consequences of Wood Harvesting, The Socio-Economic Impacts of Wood Harvesting, The Quality Requirements Imposed on the to-be-chipped Wood Material, Controlling of the Harvesting Operation and Delivery Logistics, and Availability of Wood in the Vicinity of End-use Facility. 

List of original articles:

Laitila, J. & Asikainen, A. 2006. Energy wood logging from early thinnings by harwarder method. Baltic Forestry. 12(1): 94-102. 

Laitila, J., Asikainen, A. & Nuutinen, Y. 2007. Forwarding of whole trees after manual and mechanized felling bunching in pre-commercial thinnings. International Journal of Forest Engineering 18(2): 29-39. 

Laitila, J. 2008. Harvesting technology and the cost of fuel chips from early thinnings. Silva Fennica 42(2): 267–283.  http://www.metla.fi/silvafennica/full/sf42/sf422267.pdf

Laitila, J., Heikkilä, J. & Anttila, P. 2010. Harvesting alternatives, accumulation and procurement cost of small-diameter thinning wood for fuel in Central-Finland. Silva Fennica 44(3): 465–480.                                     

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