Volume 17, numéro 2, july 2006

EN :

Multiple entries into forest stands are often needed for fire hazard reduction and ecosystem restoration treatments in the Inland-Northwest U.S.A. region. However, soil compaction occurring from mechanized harvesting operations often remains for many years and may contribute to a decline in long-term site productivity. A controlled experiment on a silt loam soil was conducted to determine (a) the effectiveness of logging slash to buffer compaction, (b) the influence of the number of machine passes, and (c) the contribution of soil moisture to changes in penetration resistance during a cut-to-length harvest in northern Idaho. Penetration resistance was measured at three soil depths (10, 20, and 30 cm) for three different moisture contents (low, medium, and high) and slash amounts (none, light, and heavy) after each of 12 machine passes (one pass each with a harvester and an empty forwarder, and 10 passes with a fully-loaded forwarder). At all three soil depths the main effect of moisture content and machine passes on penetration resistance was significant, but slash amounts alone did not significantly affect penetration resistance. After 12 passes, we measured the greatest penetration resistance in the medium soil moisture treatment at 5 to 15 cm of soil depth. When evaluated at similar moisture contents after harvesting, the soil that was driest during machine traffic (low moisture treatment) had the lowest penetration resistance. Slash was important for protecting the soil against compaction in the medium and high soil moisture treatments. Penetration resistance did not significantly increase after the second pass of a fully-loaded forwarder (31,752 kg) at any moisture content or slash level. Managing felling operations to take advantage of dry soil conditions or using slash when soils are moist may help reduce ruts and avoid long-term compaction impacts on this soil type.

EN :

Almost all timber in Ireland is harvested using mechanical harvesting heads. All new harvesters come equipped with computerized measurement systems. The objective of the research reported in this article was to assess the impact of calibration on the accuracy of harvester head measurement systems in Irish forestry conditions. The research was carried out on a site in Co. Cork. The harvester was a Timberjack 1270D with a 762C harvester head and the Timbermatic 300 control and measurement system. The harvester measurement system was assessed on its accuracy in measuring the length and volume of individual stems and logs in 9 check runs of 7 or 8 stems. The harvester head measurements were compared to values obtained by caliper-and-tape measurements. The main point that can be taken from this research is that regular calibration will greatly improve the accuracy of the harvester measurement system.

After calibration, length measurement by the harvester measurement system of individual logs was very accurate, while volume measurement was unsatisfactory for the pulp log assortment. The differences between the harvester measurements and the caliper-and-tape measurements fluctuated greatly, varying from positive to negative differences within a check run, even after calibration. These fluctuations could indicate an inherent problem associated with the design of the calibration procedure, as the positive and negative differences cancel each other out and the calibration, based on mean values, appears to indicate accurate measurements. More work needs to be done on reducing to impact of the roughness and branchiness of smaller dimension logs on the accuracy of diameter and length measurements in Irish conditions.

EN :

The layout of forest roads to access cut trees is often done manually in tropical forests, yielding suboptimal road networks with respect to the building cost. An alternative consists in using numerical optimization techniques to find a solution to this problem, also known as the multiple target access problem (MTAP). We used six numerical methods, three of which were found in the literature, to solve the MTAP. The six methods were compared on the basis on the building cost of the road network that they create, and on the basis of the computing time. They were used to solve randomly generated MTAP and also to solve a real case-study in an Indonesian rain-forest at Bulungan. The method that yielded the lowest building cost also required the longest computing time. Its computing time is actually so long that this method cannot be used in real situations. The fastest method poorly minimized the building cost. Among the four remaining methods, two methods were faster than the two others (by a factor 1.5 and 2). One of these two faster methods also yielded the lowest building costs among the four remaining methods

EN :

The prioritization of road maintenance projects is an important forest engineering task due to limited budgets and competing investment needs. Large investments are made each year to maintain and upgrade forest road networks to meet economic and environmental goals. Many models and guidelines are available for single-criteria analysis of forest roads, however we have found no method for multi-criteria analysis. Additionally, even single criteria approaches often rely on expert judgment to inform models of user preferences and priorities. These preferences are used to make tradeoffs between alternatives that contain data that are physical and biological, quantitative and qualitative, and measured on many different scales. The Analytic Hierarchy Process (AHP) has the potential to provide a consistent approach to the ranking of forest road investments based on multiple criteria. AHP was specifically developed to provide a consistent, quantifiable approach to problems involving multi-criteria analysis, but it has not been applied to road management. AHP is composed of four steps: the hierarchical decomposition of a problem into a goal, objectives, and sub-objectives; the use of a pairwise comparison technique to determine user preferences; the scaling of attribute values for each of the alternatives; and the ranking of alternatives. The road investment problem differs from traditional AHP applications in that potentially thousands of alternatives are compared at one time. We discuss the AHP methodology including the foundations, assumptions, and potential for use in prioritizing forest road investments to meet economic and environmental goals, drawing from an example from the Oregon State University College Forests.

EN :

Cable yarding continues to be an efficient and effective harvesting system for the extraction of timber on steep terrain. Modern European silvicultural strategies result in smaller harvest areas, lower extraction volumes and a shift from clear-cut to thinning operations or single tree extraction. Yarder installation time has, especially as a proportion to the extraction time, increased significantly, resulting in higher extraction costs. This study recorded the set-up and take-down time of 79 cable yarder installations. Another 76 installation times were taken from previously published time studies, for a total sample size of 155. The factorial study design differentiated uphill-or downhill yarding, yarder size and whether or not it was the first installation at a landing, or subsequent parallel installation from the same landing area. The covariates recorded were corridor length, terrain slope, number and height of intermediate supports, and number of forest workers. Both a set-up and take-down time models were developed. This will help estimate future cable installation time requirements, and more importantly, provide improved cost estimates for the new silvicultural treatments.