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  • 1.
    Johansson, Marie
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Ormarsson, Sigurdur
    Technical University of Denmark.
    Influence of growth stresses and material properties on distortion of sawn timber – Numerical investigation.2009In: Annals of Forest Science, ISSN 1286-4560, E-ISSN 1297-966X, Vol. 66, no 6, article id 604Article in journal (Refereed)
  • 2.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Pot, Guillaume
    LaBoMaP, France.
    Viguier, Joffrey
    LaBoMaP, France.
    Faydi, Younes
    LaBoMaP, France.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Performance of strength grading methods based on fibre orientation and axial resonance frequency applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.)2018In: Annals of Forest Science, ISSN 1286-4560, E-ISSN 1297-966X, Vol. 75, no 4, article id 102Article in journal (Refereed)
    Abstract [en]

    Key messageMachine strength grading of sawn timber is an important value adding process for the sawmilling industry. By utilizing data of local fibre orientation on timber surfaces, obtained from laser scanning, more accurate prediction of bending strength can be obtained compared to if only axial vibratory measurements are performed. However, the degree of improvement depends on wood species and on board dimensions. It is shown that a model based on a combination of fibre orientation scanning and axial vibratory measurement is very effective for Norway spruce (Picea abiesL.) and Douglas fir (Pseudotsuga menziesii(Mirb.) Franco). For European oak (Quercus petraea(Matt.) Liebl./Quercus roburL.) boards of narrow dimensions, axial vibratory measurements are ineffective whereas satisfactory results are achieved using a model based on fibre orientation.ContextMachine strength grading of sawn timber is an important value adding process for the sawmilling industry.AimsThe purpose of this paper has been to compare the accuracy of several indicating properties (IPs) to bending strength when applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.).MethodsThe IPs were determined for a set of data comprising scanned high-resolution information of fibre orientation on board surfaces, axial resonance frequency, mass and board dimensions.ResultsWhereas dynamic axial modulus of elasticity (MoE) gave good prediction of bending strength of Norway spruce (R-2=0.58) and Douglas fir (R-2=0.47), it did not for narrow dimension boards of oak (R-2=0.22). An IP based on fibre orientation gave, however, good prediction of bending strength for all three species and an IP considering both dynamic axial MoE and local fibre orientation for prediction of bending strength gave very good accuracy for all species (Norway spruce R-2=0.72, Douglas fir R-2=0.62, oak R-2=0.59). Comparisons of results also showed that scanning of fibre orientation on all four sides of boards resulted in more accurate grading compared to when only the two wide faces were scanned.ConclusionData of local fibre orientation on wood surfaces give basis for accurate machine strength grading. For structural size timber of Norway spruce and Douglas fir, excellent grading accuracy was achieved combining such data with data from vibratory measurements. The improvements achieved enable substantial increase of yield in high-strength classes.

  • 3.
    Wolf, Annett
    Linnaeus University, The University Administration. ETH, ETH Zentrum, CHN, CH-8092 Zurich, Switzerland.
    Determining the rate of change in a mixed deciduous forest monitored for 50 years2011In: Annals of Forest Science, ISSN 1286-4560, E-ISSN 1297-966X, Vol. 68, no 3, p. 485-495Article in journal (Refereed)
    Abstract [en]

    Trees in two compartments of the mixed deciduous forest Draved Forest have been monitored regularly for 50 years. This data set was used to study the rate of change in forest structure and composition applying the Kolmogorov-Smirnov statistics, chi-square test for the goodness of fit, and principal component analysis. We also correlated the specific test statistics with other forest properties to elucidate the importance of various factors for the observed changes in forest structure. After 50 years, the still significant changes in the forest structure and species composition indicate that the compartments have not reached the state of an old growth forest. Although some measures indicated that the compartments were approaching this stage, other showed the opposite response and even an increasing rate of change. As the three statistical methods contributed in different ways, we recommend the combination of several statistical methods to assess changes in the forest structure.

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