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Silva Fennica 1926-1997
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Articles by Lars Eliasson

Category: Research article

article id 6993, category Research article
Lars Fridh, Lars Eliasson, Dan Bergström. (2018). Precision and accuracy in moisture content determination of wood fuel chips using a handheld electric capacitance moisture meter. Silva Fennica vol. 52 no. 5 article id 6993. https://doi.org/10.14214/sf.6993
Highlights: The studied capacitance meter can provide accurate estimates of mean moisture content for chips with M < 50% if a large sample is taken; It should be possible to use the capacitance meter to measure moisture content even for calculating payments depending of the needed accuracy; However a calibration function for each assortment is needed.

According to the Swedish Timber Measurement Act, measurements affecting payments for wood fuels to landowners must be accurate and precise. In this regard, moisture content is an important quality parameter for wood chips which influences the net calorific value as received and thus the economic value. As standard practice moisture content is determined with the oven-drying method, which is cumbersome to use for deliveries to facilities without drying-ovens, which in turn necessitates that samples are taken elsewhere for measurement. An alternative solution is to use a portable moisture meter. Our aim was to evaluate the precision of a handheld capacitance moisture meter. Accuracy and precision of a capacitance meter was determined in the lab and a calibration function was made. Thereafter, the calibrated moisture meter was compared with the standard method for moisture content determination of truckloads of chips. The capacitance meter showed a moderate accuracy by underestimating moisture content by 6.0 percentage points (pp), compared to the reference method, at a precision of ±3.8 pp (CI 95%). For chips with M > 50%, both accuracy and precision decreased. Calibration increased the accuracy in the follow up study by 3 pp for chips with M < 50% but could not be made for wetter chips. The oven-drying method and the capacitance meter can provide equally accurate estimates of mean moisture content for chips with M < 50% if a larger sample is taken with the latter. It should be possible to use capacitance meters to measure moisture content even when used to calculate payments depending of the needed accuracy. A calibration function for each assortment is needed.

  • Fridh, Skogforsk, The Forestry Research Institute of Sweden, Uppsala Science Park, 751 83 Uppsala, Sweden; Skogsägarna Mellanskog, Uppsala Science Park, Box 127, 751 04 Uppsala, Sweden ORCID ID: http://orcid.org/0000-0002-4721-1193 E-mail: lars.fridh@mellanskog.se
  • Eliasson, Skogforsk, The Forestry Research Institute of Sweden, Uppsala Science Park, 751 83 Uppsala, Sweden ORCID ID: http://orcid.org/0000-0002-2038-9864 E-mail: lars.eliasson@skogforsk.se (email)
  • Bergström, Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, S-901 83 Umeå, Sweden ORCID ID:E-mail: dan.bergstrom@slu.se
article id 2018, category Research article
Sima Mohtashami, Lars Eliasson, Gunnar Jansson, Johan Sonesson. (2017). Influence of soil type, cartographic depth-to-water, road reinforcement and traffic intensity on rut formation in logging operations: a survey study in Sweden. Silva Fennica vol. 51 no. 5 article id 2018. https://doi.org/10.14214/sf.2018
Highlights: Soil type and traffic intensity had significant effects on rut formation; Further studies are required to identify all factors affecting rut formation, especially on soils with medium bearing capacity; The cartographic depth-to-water index (DTW) alone did not predict rut formation, but used in combination with other information, e.g. soil type, could be an interesting tool for delineating soil areas that are potentially vulnerable to rut formation in logging operations.

Rut formation caused by logging operations has been recognised as a challenge for Swedish forestry. Frequent traffic with heavy machines on extraction roads, together with a warmer climate, is one of the factors that increases the risk of rut formation in forests. One possible way to control this impact of logging operations is to design and apply decision support tools that enable operators to take sensitive areas into account when planning extraction roads. In this study, 16 different logging sites in south-eastern Sweden were surveyed after clear-cut. Information was collected about extraction roads (i.e. traffic intensity, whether the roads had been reinforced with slash) and ruts. Digital maps such as cartographic depth-to-water (DTW) index and soil type were also examined for any connection to rut positions. Soil type and traffic intensity were found to be significant factors in rut formation, while DTW and slash reinforcement were not. However, the DTW map combined with other information, such as soil type, could contribute to decision support tools that improve planning of extraction roads.

  • Mohtashami, The forestry research institute of Sweden, Skogforsk, Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID:E-mail: sima.mohtashami@skogforsk.se (email)
  • Eliasson, The forestry research institute of Sweden, Skogforsk, Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID: http://orcid.org/0000-0002-2038-9864 E-mail: lars.eliasson@skogforsk.se
  • Jansson, The forestry research institute of Sweden, Skogforsk, Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID: http://orcid.org/0000-0002-3018-9161 E-mail: gunnar.jansson@skogforsk.se
  • Sonesson, The forestry research institute of Sweden, Skogforsk, Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID: http://orcid.org/0000-0002-2018-7496 E-mail: johan.sonesson@skogforsk.se
article id 930, category Research article
Raffaele Spinelli, Eugenio Cavallo, Lars Eliasson, Alessio Facello. (2013). Comparing the efficiency of drum and disc chippers. Silva Fennica vol. 47 no. 2 article id 930. https://doi.org/10.14214/sf.930
The study compared the effect of chipper type on productivity, power demand, fuel consumption and product quality. Tests were conducted on two commercial chipper models, a disc and a drum chipper. Both chippers had the same diameter capacity, were applied to the same tractor and fed with the same feedstock types. Fifteen replications were conducted per machine and for each of four different feedstock types, reaching a total of 120 tests. The disc chipper had a higher energy efficiency and used 19% less fuel per unit product, possibly due to its simpler design, integrating comminuting and discharge system in one synergic device. In contrast, the drum chipper was 8% more productive, since it cut with the same energy all along the length of its knives. The drum chipper produced smaller chips, with a higher incidence of fines. Feedstock type had a strong effect on productivity, energy efficiency and product quality. The effect of feedstock type was mainly related to piece size, and may be stronger than the effect of chipper type. Further studies should determine the effect of blade wear on the relative performance of the two chipper types.
  • Spinelli, CNR IVALSA, Via Madonna del Piano 10, Sesto Fiorentino (FI), Italy ORCID ID:E-mail: spinelli@ivalsa.cnr.it (email)
  • Cavallo, CNR IVALSA, Via Madonna del Piano 10, Sesto Fiorentino (FI), Italy ORCID ID:E-mail: e.cavallo@imamoter.cnr.it
  • Eliasson, Skogforsk, Uppsala Science Park, SE-751 83 Uppsala, Sweden ORCID ID:E-mail: lars.eliasson@skogforsk.se
  • Facello, CNR IVALSA, Via Madonna del Piano 10, Sesto Fiorentino (FI), Italy ORCID ID:E-mail: a.facello@ima.to.cnr.it
article id 343, category Research article
Karin Vestlund, Tomas Nordfjell, Lars Eliasson, Anders Karlsson. (2006). A decision support system for selective cleaning. Silva Fennica vol. 40 no. 2 article id 343. https://doi.org/10.14214/sf.343
Cleaning (pre-commercial thinning) costs have increased relative to logging and regeneration costs, creating a desire for rationalisation. Cleaning with robots may be a solution, but automating stem selections requires a decision support system (DSS) capable of rendering acceptable results. The aims were to develop a DSS for automation of individual stem selections in practical cleaning, and to test, using simulations, if it renders acceptable results. Data on 17 young forest stands were used to develop a DSS that selects stems by species, position (including distance and density parameters), diameter, and damage. Six simulations were run, following the DSS, with different target settings for density, percentage of deciduous stems and minimum distance between stems. The results depend on the initial state of the stands, but generally met the requested targets in an acceptable way. On average, the density results deviated by –20% to +6% from the target values, the amount of deciduous stems shifted towards the target values, and the proportion of stems with defined damaged decreased from initially 14–90% to 4–13%. The mean diameter at breast height increased and the minimum allowed distance between stems was never violated. The simulation results indicate that the DSS is operational. However, for implementation in robotics a crucial problem is to automatically perceive the selected attributes, so additional simulations with erroneous data were run. Correct measurements of diameters are less crucial than to find the majority of the trees and the majority of trees with damages.
  • Vestlund, Swedish University of Agricultural Sciences, Department of Silviculture, P.O. Box 7060, SE-750 07 Uppsala, Sweden ORCID ID:E-mail: karin.vestlund@ssko.slu.se (email)
  • Nordfjell, Swedish University of Agricultural Sciences, Department of Forest Resource Management and Geomatics, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Eliasson, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Karlsson, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
article id 366, category Research article
Lars Eliasson. (2005). Effects of forwarder tyre pressure on rut formation and soil compaction. Silva Fennica vol. 39 no. 4 article id 366. https://doi.org/10.14214/sf.366
In Swedish forestry, final felling is usually done by a harvester and a forwarder. These machines are heavy and the risk for rutting and soil compaction can be considerable under unfavourable soil conditions. The aim of this study was to evaluate effects of forwarder tyre inflation pressure on rutting and soil compaction after final felling. Three levels of forwarder tyre pressure were studied, 300, 450 and 600 kPa, after 2 and 5 machine passages. The first passage was driven with a 19.7 Mg harvester, and the second to fifth passages with a fully loaded forwarder totalling 37.8 Mg. Rut depths were not significant affected by tyre pressures but increased significantly with the number of machine passages. Soil density was significantly increased by 0.075 Mg m–3 by the harvester passage. Soil density increased significantly with increasing number of forwarder passages, and tyre pressure did not significantly influence this increase but the interaction between number of forwarder passages and tyre pressure was almost significant. Data suggest that density increases occur earlier in the 600 kPa treatment than in the other treatments. Only parts of an area harvested are trafficked in a normal harvesting operation. Outside the research area approximately 12.5 per cent of the area harvested was covered with ruts. On primary strip roads, which are heavily trafficked, soil compaction cannot be avoided by reducing the tyre pressure. On secondary strip roads, not passed more than once by the forwarder, a low forwarder tyre pressure may reduce soil compaction.
  • Eliasson, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail: lars.eliasson@norraskogsagarna.se (email)
article id 363, category Research article
Karin Vestlund, Tomas Nordfjell, Lars Eliasson. (2005). Comparison of human and computer-based selective cleaning. Silva Fennica vol. 39 no. 4 article id 363. https://doi.org/10.14214/sf.363
In silvicultural tending operations like cleaning (pre-commercial thinning), the results are irreversible, so it is important for the decisions to be consistent with the aims for the stand. To enable operational automatic stem selections, a decision support system (DSS) is needed. A previously presented DSS seems to render acceptable cleaning results, but needs further analysis. The aims of the study were to compare the cleaning results of experienced cleaners and DSS simulations when “similar” instructions were given, and to assess the usefulness and robustness of the DSS. Twelve experienced cleaners were engaged to “clean” (mark main stems) six areas; each cleaner “cleaned” two areas. The DSS was used to generate two computer-based cleanings (simulations) of these areas. Four laymen also “cleaned” one of the areas following the DSS. The density results were significantly affected by the areas’ location, whereas the proportions of deciduous stems and damaged stems were significantly affected by both the areas’ location and method, i.e. manual “cleaning” and general or adjusted simulation. The study showed that the DSS can be adjusted so that the results are comparable with the cleaners’ results. Thus, the DSS seems to be useful and flexible. The laymen’s results were close to the results of the “general” simulation, implying that the DSS is robust and could be used as a training tool for inexperienced cleaners. The DSS was also acceptable on a single-tree level, as more than 80% of the main-stems selected in the simulations were also selected by at least one cleaner.
  • Vestlund, Swedish University of Agricultural Sciences, Department of Silviculture, P.O. Box 7060, SE-750 07 Uppsala, Sweden ORCID ID:E-mail: karin.vestlund@ssko.slu.se (email)
  • Nordfjell, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Eliasson, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
article id 428, category Research article
Jonny Andersson, Lars Eliasson. (2004). Effects of three harvesting work methods on Harwarder productivity in final felling. Silva Fennica vol. 38 no. 2 article id 428. https://doi.org/10.14214/sf.428
During the last ten years interest in the harwarder has increased, however, studies have concentrated on effects of technical improvements on machine productivity. It has been noted that there is a large potential to increase the productivity through development of suitable work methods. To find efficient work patterns for a harwarder with a turnable loading area, three different harvesting methods were studied in final felling. Three work methods were used. Method 1: the harwarder drove backwards into the stand making a strip road, strip road trees were felled and left on the ground, on the way out of the stand the harwarder cut and processed the trees on both sides of the machine directly into the loading area. Method 2: the harwarder drove forward along the edge of the cut, cutting and processing trees directly into the loading area. Method 3: the harwarder drove forward into the stand and cut and processed strip road trees and trees standing on both sides of the machine directly into the loading area. The most efficient work method was method 2 where the productivity was 13.0 m3 u.b. per E0h (cubic metre under bark per effective hour). The productivities for method 1 and 3 were 12.1 and 11.9 m3 u.b. per E0h, respectively. In addition to work method harwarder productivity was shown to be dependent on load volume, average tree size and hauling distance. The only work elements significantly affected by work methods were processing and movement during processing. The operator had only a few weeks to get used to the machine and even less time to practise on the work methods. Thus, it is probable that the productivity for the studied methods will increase with increasing work experience. Furthermore, as only three work methods were studied, there are still untested work methods. The potential to further improve harwarder work methods is considerable.
  • Andersson, Swedish University of Agricultural Sciences, Department of Silviculture, S-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Eliasson, Swedish University of Agricultural Sciences, Department of Silviculture, S-901 83 Umeå, Sweden ORCID ID:E-mail: lars.eliasson@ssko.slu.se (email)

Category: Research note

article id 379, category Research note
Daniel Ligné, Lars Eliasson, Tomas Nordfjell. (2005). Time consumption and damage to the remaining stock in mechanised and motor manual pre-commercial thinning. Silva Fennica vol. 39 no. 3 article id 379. https://doi.org/10.14214/sf.379
Selective pre-commercial thinning (PCT) is usually carried out by workers with a brush saw in order to increase the growth of the potential crop trees (main stems) through removal of competing trees. In the last decade relative PCT costs have increased, partly because stands are denser and have higher trees when treated, which has led to new interest for mechanised PCT. The objective was to compare mechanised and motor manual PCT regarding productivity and damage to remaining main stems. Time consumption for, and damage after, mechanised and motor manual PCT were studied on 50 plots per treatment in mixed pine birch stands with an initial stand density exceeding 4500 stems ha–1. In the present study productivity was influenced by stand density, stand height and the quota between height and diameter. Irrespectively of these factors, mechanised PCT was 0.74 hours ha–1 slower than motor manual PCT. Motor manual PCT of the average stand (average height 3.69 m, 10 816 stems ha–1) took 5.06 effective hours. In average 2475 and 2805 main stems ha–1 were left after the mechanised and motor manual treatments, respectively, whereof 1.3 and 2.1% were damaged by the treatments. The results show that efficiency in motor manual PCT has increased in dense and tall stands compared to older studies. Motor manual PCT was more time effective than mechanised PCT, and thereby also even more cost-effective. However, the potential for technical and methodological development of mechanised PCT is probably larger than for motor manual PCT.
  • Ligné, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail:
  • Eliasson, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail: lars.eliasson@norraskogsagarna.se (email)
  • Nordfjell, Swedish University of Agricultural Sciences, Department of Silviculture, SE-901 83 Umeå, Sweden ORCID ID:E-mail:

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