Volume 21, numéro 1, january 2010

EN :

We compared value recovery of a modified treelength (MTL) logging system that measures product diameter and length using a Waratah 626 harvester head to that of a treelength (TL) system that estimates dimensions. A field test compared the actual value cut to the maximum potential value suggested by the log bucking optimization program Assessment of Value by Individual Stems (AVIS) for 25 felled trees on each of three sites for two loggers. One half of each site was harvested with a TL crew and the other half with a MTL crew. ANOVA on individual stems using site as a blocking factor showed significant differences between TL and MTL, with TL recovering 80.3% and MTL recovering 73.7% of total value after downgrades.

EN :

Much of the forest industry in the western United States does not require control of compaction on forest road subgrades despite the potential economic and environmental gains from improved subgrade construction. Development of tools such as the Clegg impact hammer allow for rapid testing of the subgrade during construction, and Clegg Impact Values (CIV) have been correlated with more robust soil test values such as the California Bearing Ratio (CBR) that are often used for road design. A new correlative model that relates the CBR to 20 kg CIV was developed entirely from field data, differing from previously developed models that used laboratoryprepared soils. Another advantage of this model is that it uses a 20kg Clegg impact hammer. The 20kg Clegg impact hammer has a larger testing area than the more common 4.5kg Clegg impact hammer; thus, there is less influence from small deviations in the soil matrix due to items in the fill such as rocks or organic matter. The correlation coefficient for this model is 0.71, which is lower than that for models previously developed from laboratory results. The use of a lower bound, onetailed, 90% confidence limit is presented as a useful design model to determine a conservative of soil strength that can be measured directly during construction.

EN :

The existence of considerable productivity differences between operators is well known in forestry work studies. Several techniques have been developed to manage operator (i.e. interindividual) effects and thus enable general conclusions to be drawn. In the Nordic countries interindividual variations have generally been managed by using “withinoperator” comparisons. The methodology is equivalent to the statistical method of blocking, when defining each operator as a block effect. Unfortunately this approach has traditionally been referred to as “comparative studies,” although it only addresses one of many possible components of genuine comparative work studies. In the traditional motivation for usage of operator blocking it is assumed that productivity relationships between work methods are independent of the operator if the same operator works with both methods. Hence, comparisons of relative productivity should ignore interindividual variations, enabling universal productivity relationships between methods/conditions of interest to be determined. Unfortunately this assumption has often been taken literally, with expectations of productivity relationships to be identical between individuals instead of on a population level. In this article the literal approach is scrutinized using the time taken by 12 operators to undertake various tasks in an experimental study of firewood processing with different machine systems and round wood types. Operators, as a population, did respond in a similar manner to treatments, but there was great variation between individuals. Hence, the assumptions of literally uniform individual productivity relationships should, therefore, be replaced by a population based theoretical foundation, which justifies the continued use of operator blocking to objectively handle the inevitable operator effect in forestry work studies.

EN :

In many boreal countries forest biomass from dense young stands has great potential to meet growing demands for bioenergy. However, there is currently no costeffective operational system for harvesting such stands. When harvesting, it would be desirable to compress trees and leave some of the foliage and fine branches in the stand in order to reduce extraction of nutrients and improve the harvested material's fuel properties from a reduced ash content point of view. The objectives were to evaluate experimental systems (a boomtip mounted unit for processing bunches, and a small prototype forwarder for compressing loads) in terms of their utility for compressing and partially debranching fresh and stored bunches of Scots pine trees and compressing forwarder loads of fresh Scots pine and birch trees. Processing of fresh bunches resulted in mass losses of about 10% (dbhclass 58 cm; not significant) to 15% (dbhclass 1215 cm; significant) with 35 to 50% reductions in ash contents and increases in bulk and net energy density of about 80 to 160%. Instand storage of bunches before processing generally yielded no significant advantages except for a 10%unit reduction in moisture content. Compression of forwarder loads resulted in 16 (pine) to 32% (birch) increases in load densities, with a significant increase for birch trees.

The described techniques facilitate productivity increases of offroad and road transport of tree parts, and a substantial proportion of the ashrich materials such as needles and fine branches are left in the stand. If both tested techniques are applied during the harvesting of young trees the benefits would be substantial.

EN :

Western juniper (Juniperus occidentalis) is considered a relatively untapped source of woody biomass with potential to serve as a significant feedstock for regional woodtoenergy systems. A barrier to further development of this market is a lack of information concerning the productivity and costs of juniper harvesting systems. One published study and three unpublished case studies of harvesting western juniper are compared using consistent stand and site variable values and machine costs. Felling, skidding, and log processing processes are compared across a range of conditions. Stump to landing harvesting costs for average conditions ranged from approximately $35/tonne($32/ton) to $96/tonne($87/ton), averaging $74/tonne($67/ton). A lack of robust estimators of juniper volume is identified as a critical research need to aid in the development of western juniper as a woody biomass feedstock.

EN :

Detailed timeandmotion studies were conducted on a harvesting system that included rolloff bins and bunks used in conjunction with a Timbco harwarder at two study sites in western Montana. Data from these studies were used in multiple regression analysis to develop production equations for total cycle time for each of the seven processes involved in harvesting roundwood products and woody biomass. Independent variables used to create these production equations included distance traveled, piece size, number of pieces, and a site term. Comparisons were made between developed equations from this study and other published equations. Using standardized variables, production rates (tons/hour) of the observed processes were developed. Forest managers can apply these equations to determine the cycle time for a process and, when paired with tons per cycle, the production rate of the rolloff and hooklift system can be determined and compared to other roundwood and biomass harvesting and treatment options.