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  • 1.
    Adamopoulos, Stergios
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sjöberg, Samuel
    Relationship between ultrasonic velocity and spiral grain in standing hybrid aspen trees2016In: Proceedings of the Hardwood Conference, Eco-efficient Resource Wood with Special Focus on Hardwoods, 8-9 September, 2016, Sopron, Sopron: University of West Hungary Press , 2016, p. 22-23Conference paper (Refereed)
  • 2.
    Eklund, Leif
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, Institutionen för biovetenskaper och processteknik.
    Säll, Harald
    Växjö University, Faculty of Mathematics/Science/Technology, Institutionen för industriella produktionssystem.
    The influence of wind on spiral grain formation in conifer trees2000In: Trees, ISSN 0931-1890, E-ISSN 1432-2285, Vol. 14, p. 324-328Article in journal (Refereed)
    Abstract [en]

    The correlation between spiral grain formationand crown asymmetry was investigated in 18 Scots pine(Pinus sylvestris L.) and 17 Norway spruce [Picea abies(L.) Karst.] trees selected from clones of each speciesgrowing in the south of Sweden. The angle between thelongitudinal direction of the tracheids in the outermostyear ring compared to the longitudinal direction of thestem was measured by scribing lines which followed thedirection of the tracheids. The crown asymmetry wasmeasured by taking photographs of the trees followed bya simple picture analysis of the tree. Wind data for thegrowing seasons of 1997 and 1998 were obtained fromthe Swedish Meteorological and Hydrological Institute.The results showed a significant correlation between theangle of the tracheids compared to the stem longitudinaldirection going from a left-handed angle if the trees hada crown projected to the north towards a right-handedangle the more the crown projects to the south.

  • 3.
    Eklund, Leif
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, Institutionen för biovetenskaper och processteknik.
    Säll, Harald
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Kliger, Robert
    Chalmers University of Technology, Sweden.
    Spiral grain from an environmental, genetic and economical point of view2000In: The Tree, 2000Conference paper (Other academic)
    Abstract [en]

    Characteristic of wood is that its behavior is strongly orthotropic due to the internal structure of the material and dependent on moisture and temperature. In addition, the material is characterized by a strong variation of the properties in the radial direction.  Another important property that affects the behavior of wood is spiral grain, causing the direction of the fibers to deviate from the longitudinal direction of the tree. It is hardly possible to assess spiral grain in the woods, no rejection of severe spiraled trees are done before the log arrives into the sawmill. If a method for on site rejection is available, and the severest spiraled trees, 2-10%, could be avoided in the shipment to the sawmill substantial money could be saved in the forest industry. The causes of spiral grain have been thoroughly discussed through the years and the debate about the environmental and genetic impact on the phenomenon is still not settled. We present evidence for a direct effect of wind on the degree of spiral grain. We also present evidence for a putative thinning effect on spiral grain that is probably connected to wind. Additionally we also present evidence for a strong genetic impact on the formation of spiral grain in conifer trees. In another study mechanical properties such as shape stability has been investigated for the same trees. In some of the logs it may therefore be possible to quantify the relation between spiral grain and distortion in sawn timber.

  • 4.
    Eklund, Leif
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, Institutionen för biovetenskaper och processteknik.
    Säll, Harald
    Växjö University, Faculty of Mathematics/Science/Technology, Institutionen för industriella produktionssystem.
    Linder, Sune
    Swedish University of Agricultural Sciences, Sweden.
    Enhanced growth and ethylene increases spiral grain formationin Picea abies and Abies balsamea trees2003In: Trees, ISSN 0931-1890, E-ISSN 1432-2285, Vol. 17, no 1, p. 81-86Article in journal (Refereed)
    Abstract [en]

    Spiral grain angle in Norway spruce (Piceaabies) trees and balsam fir (Abies balsamea) seedlingswas investigated in relation to growth rate, endogenousand applied ethylene. Trees from stands of Norwayspruce, which were irrigated and fertilised in order to enhancegrowth, and trees having different growth rates innon-treated stands were studied. Stem growth rate at thestand level (m3 ha–1 year–1) was measured annually, orby means of microscopy on stem sections as the numberand size of tracheids produced. Enhanced growth increasedethylene evolution and maintained a high levelof left-handed spiral grain angle in comparison to slower-growing trees. An increased number of earlywoodtracheids in fast growing trees was correlated to a moreleft-handed spiral grain angle. Ethrel, applied to stems ofbalsam fir seedlings, increased the internal ethylene levelsin parallel with increased left-handed spiral grain angle.The results indicate that ethylene regulates the extentof spiral grain angle.

  • 5.
    Gjerdrum, Peder
    et al.
    Norwegian Forest Research Institute, Norway.
    Säll, Harald
    Växjö University, Faculty of Mathematics/Science/Technology, Institutionen för industriella produktionssystem.
    Storö, Hans Martin
    North Tröndelag Research Institute, Norway.
    Spiral grain in Norway spruce: constant change in grain angle in Scandinavian sawlogs2002In: Forestry (London), ISSN 0015-752X, E-ISSN 1464-3626, Vol. 75, no 2, p. 163-170Article in journal (Refereed)
    Abstract [en]

    Any evident grain deviation will reduce strength and increase warp in sawn timber. To describe the magnitude and variance of grain angle in Norway spruce, specimens from 1046 Norwegian sawlogs and 380 logs from Sweden and Finland were examined. For individual specimens, grain angle outside the innermost zone closest to the pith might be expressed by a simple linear function of radial distance from the pith. The intercept and inclination of this function are close to bivariate normally distributed with mean values (SD) of 2.7° mm−1 (1.9) and −0.039° mm−1 (0.037), respectively. Inclination is less negative for wider annual rings (r = 0.3), and intercept and inclination are negatively correlated (r = −0.4). The constant rate of change indicates inherited property rather than influence of any dynamic, external stimulus. No predictor for grain angle pattern was found. The linear model leads to simplifications both when observing the grain angle in the forestry, and in calculations of strength properties and distortion in the timber industry.

  • 6.
    Hallingbäck, Henrik R.
    et al.
    Swedish University of Agricultural Sciences.
    Högberg, Karl-Anders
    The Forestry Research Institute of Sweden.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Lindeberg, Johan
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Jansson, Gunnar
    The Forestry Research Institute of Sweden.
    Optimal timing of early genetic selection for sawn timber traits in Picea abies2018In: European Journal of Forest Research, ISSN 1612-4669, E-ISSN 1612-4677, Vol. 137, no 4, p. 553-564Article in journal (Refereed)
    Abstract [en]

    In breeding Norway spruce, selection for improved growth and survival is performed at age 10-15 years in order to optimize genetic gain per year. We investigated whether a selection based on wood traits such as density and grain angle, measured under bark in the field at the same age would be informative enough with respect to structural quality traits of sawn boards. To achieve this objective, a sawing study was conducted on the butt logs of 401 trees from a 34-year-old Norway spruce progeny trial situated in southern Sweden. Stem discs were excised from the top of the logs and radial profile data of grain angle, and wood density was recorded for specific annual rings. The sawn and dried boards were assessed for structural traits such as twist, board density, bending stiffness (static modulus of elasticity, sMoE) and bending strength (modulus of rupture, MoR). Additive genetic correlations (r (a)) between single annual ring density measurements and board density, sMoE and MoR were consistently strong (r (a)> 0.7) for annual rings 5-13. Genetic correlations of similar magnitude between grain angle and board twist were estimated for all investigated annual rings (from 2 to around 26 under bark). Consequently, it was found that indirect selection for wood density and grain angle at the tree age 10-16 years would result in more genetic gain per year than selection at later ages. This makes it feasible to perform simultaneous selection of progeny in the field for both growth and wood traits at similar ages.

  • 7.
    Hannrup, Björn
    et al.
    Skogforsk.
    Säll, Harald
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Jansson, Gunnar
    Skogforsk.
    Genetic parameters for spiral grain in Scots pine and Norway spruce2003In: Silvae Genetica, ISSN 0037-5349, Vol. 52, no 5-6, p. 215-220Article in journal (Refereed)
    Abstract [en]

    Genetic parameters were estimated for grain angle, growth and exterior quality traits in two 18-year-old Scots pine (Pinus sylvestris L.) progeny trials and for grain angle and growth traits in two 12-year-old clonal trials of Norway spruce (Picea abies L. Karst.). Mean grain angles ranged 1.4 to 2.0 degrees and 2.1 to 2.6 degrees in the Scots pine and Norway spruce trials, respectively. Heritabilities for grain angle were high in Scots pine (h2>0.40) and moderate in Norway spruce (H2>0.30). The genetic standard deviations were around or slightly below one degree. In general, grain angle was genetically and phenotypically uncorrelated with the growth and exterior quality traits. All traits showed low amount of genotype by environment interaction and there was no tendency of grain angle being a more stable traits than the other traits studied.

     

    A newly developed measurement device for grain angle where the grain angle is revealed by a wedge that is pushed through the bark into the wood and follows the inclination of the tracheids was tested and found suitable for measurements in genetic tests.

  • 8.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Briggert, Andreas
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Growth layer and fibre orientation around knots in Norway spruce: a laboratory investigation2018In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 52, no 1, p. 7-27Article in journal (Refereed)
    Abstract [en]

    The strength of structural timber largely depends on the occurrence of knots and on the local material directions in the surroundings of such knots. There is, however, a lack of methods for establishing a full dataset of the local material directions. The present research aims at the development and application of a laboratory method to assess the geometry of growth layers and the orientation of fibres in a high-resolution 3D grid within wood specimens containing knots. The laboratory method was based on optical flatbed scanning and laser scanning, the former resulting in surface images and the latter, utilizing the tracheid effect, resulting in in-plane fibre angles determined in high-resolution grids on scanned surfaces. A rectangular solid wood specimen containing a single knot was cut from a tree in such a way that it could be assumed that a plane of symmetry existed in the specimen. By splitting the specimen through this plane through the centre line of the knot, two new specimens with assumed identical but mirrored properties were achieved. On one of the new specimens, the longitudinal-radial plane was subsequently scanned, and the longitudinal–tangential plane was scanned on the other. Then, by repeatedly planing off material on both specimens followed by scanning of the new surfaces that gradually appeared, 3D coordinate positions along different growth layers and 3D orientation of fibres in a 3D grid were obtained. Comparisons between detected fibre orientation and growth layer geometry were used for the assessment of the accuracy obtained regarding 3D fibre orientation. It was shown that the suggested method is well suited to capture growth layer surfaces and that it provides reliable information on 3D fibre orientation close to knots. Such knowledge is of great importance for understanding the properties of timber including knots. The quantitative data obtained are also useful for calibration of model parameters of general models on fibre orientation close to knots.

  • 9.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Briggert, Andreas
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology. Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Three dimensional growth layer geometry and fibre orientation around knots: a laboratory investigation2016In: Proceedings of WCTE 2016 World Conference on Timber Engineering / [ed] Eberhardsteiner, W. Winter, A. Fadai, M. Pöll, 2016Conference paper (Refereed)
  • 10.
    Högberg, Karl-Anders
    et al.
    Skogforsk.
    Hallingbäck, Henrik
    SLU.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Jansson, Gunnar
    Skogforsk.
    The potential for the genetic improvement of sawn timber traits in Picea abies2014In: Canadian Journal of Forest Research, ISSN 0045-5067, E-ISSN 1208-6037, Vol. 44, no 4, p. 273-280Article in journal (Refereed)
    Abstract [en]

    This study evaluated the potential for the selective genetic improvement of the structural quality traits important in sawn Norway spruce (Picea abies (L.) Karst.) timber based on early and nondestructively assessed field traits. From a 34-year-old Norway spruce trial situated in southern Sweden, 401 butt logs were sampled and sawn to produce two 50 × 100 mm boards that were dried to an 18% moisture content. Structural quality traits were assessed, and genetic parameters were estimated, including additive genetic variance, heritability, and their genetic correlations with field traits. Board twisting, density, and modulus of elasticity (MOE, stiffness) were found to have appreciable heritabilities (0.23–0.44). Board twist was found to have a strong genetic correlation with grain angle measured under bark in the field (0.93), and both board MOE and density exhibited strong genetic correlations with field-assessed pilodyn penetration (–0.75 and –0.91, respectively). Although these observations were made on a thinning material comprising mainly juvenile wood, they nonetheless suggest grain angle and pilodyn penetration to be promising candidates as selection criteria for Norway spruce breeding. Heritabilities of other sawn timber traits were lower and the genetic correlations between these traits and field traits were also lower, variable, and had large estimation errors.

  • 11.
    Johansson, Marie
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Lundqvist, Sven-Olof
    Innventia.
    Properties of materials from Birch – Variations and relationships: Part 2. Mechanical and physical properties2013Report (Other academic)
    Abstract [en]

    Birch regarded as Sweden’s third largest tree species. The two birch species, Silver- and Downy birch represents about 12% of total Swedish timber volume. For forestry, birch an important tree species which today mainly used for the manufacture of pulp and paper.

    The aim of this project was to describe mechanical and physical properties of birch. The properties that have been studied are stiffness, bending strength, shrinkage, spiral gran angle, density and microfibril angle in the cell wall and vessel cells, from different parts of the birch stems grown at different rates. The mapped properties have been compared also with those of other tree species, mainly spruce. The long term aim is to increase the knowledge of the birch wood properties to provide better predict their impact on products as well as provide a basis for better utilization of Swedish birch raw material and hopefully using birch as future structural timber.

    Three birch stands with different growth was chosen: Two stands where the birch growth has been different in a mixed forests stand of spruce and pine, and a fast growing stand with improved birch seedlings. Samples were taken from four different heights in the trees. The main thing that has been analyzed is the bending strength, modulus of elasticity, shrinkage coefficients in different directions and spiral grain. The mechanical tests are carried out on tines that are 20 x 20 x 300 mm and the fiber angle measurements were carried out on discs. These results have supplemented by the results of analyzes conducted with lnnventias SilviScan instruments that are able to recognize variations of year ring wood properties. Some of these are density, and microfibril angle, which is also included in this report.

    The results show that the wood from normal growth and fast growth improved birch receive equivalent wood properties. The results also show that birch wood properties are slightly better than that in Norway spruce.

    The material in this project was limited to only three stands and 11 sampled trees and therefore it can´t provide complete answers to the birch trees different wood properties. Limitations include genetic origin, growth rate, earlier silvicultural treatment and number of sample trees.

  • 12.
    Kliger, Robert
    et al.
    Chalmers University of Technology, Sweden.
    Säll, Harald
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    STUD: Improved Spruce Timber Utilizations: Prediction of Twist and Industrial Validation. Sub-task B9.1.2000Report (Other academic)
    Abstract [en]

    It has been shown that the number of straight battens after drying can be easily increased by avoiding converting logs with a somewhat large left-hand spiral grain measured under bark and by avoiding converting the central cylinder of logs with a diameter about 50 mm around the pith. It is assumed that more than 10% of the trees (Norway spruce) exceed a spiral grain angle of 3° measured under bark. Between 80% and 90% of the studs from these trees displayed an unacceptable amount of twist (3°). It should be of great interest for the sawmill industry to be able to reject logs with respect to their overly large spiral growth in order to improve the straightness of sawn lumber in service (at low moisture content).

    Other conclusion drawn from this study is that the spiral grain angle and the annual ring curvature of the stud can predict twist. If it is possible to measure effectively spiral grain angle on the logs or on the sawn timber prior to drying the twist-prone material would be possible to sort out and thus increase the value of the timber products. Simple models expressed in diagram form can produce enough information about twist to be a useful tool for improving the number of straight studs after drying.

    Over 90% of the studs sawn closer than 50 mm from the pith from five trees displayed unacceptable twist when dried to 12% moisture content. All the studs sawn from a tree (five logs) with a left-hand spiral grain of about 15° displayed very large twist after drying and they were all classified as rejects, independent of the grading criterion. 

  • 13.
    Malmqvist, Cecilia
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Wallin, Elisabeth
    Dalarna University.
    Lindström, Anders
    Dalarna University.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Differences in bud burst timing and bud freezing tolerance among interior and coastal seed sources of Douglas fir2017In: Trees, ISSN 0931-1890, E-ISSN 1432-2285, Vol. 31, no 6, p. 1987-1998Article in journal (Refereed)
    Abstract [en]

    The need for species that will grow well through ongoing climate change has increased the interest in Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] in Sweden. One of the most common problems seen in plantations of Douglas fir seedlings is damage caused by late spring frost, known to be highly correlated with the timing of bud burst. The objective of this study was to investigate spring-related bud development under Nordic conditions of seven Douglas fir provenances and to compare data with a local provenance of Norway spruce (Picea abies (L.) Karst). Results from a field trial and a greenhouse-based study were compared. The interior Douglas fir provenances exhibited an earlier bud burst than coastal provenances, both in the greenhouse and in the field trial. When comparing differences within the groups of interior and coastal Douglas fir provenances, no differences could be found. The local Norway spruce, only grown in the greenhouse, showed an intermediate bud development profile similar to the interior Douglas fir provenance Three Valley. We therefore suggest that Three Valley could be planted at the same locations as the investigated local provenance of Norway spruce in mid-Sweden. To avoid spring frost damage the Douglas fir seedlings need to be frozen stored and planted late in spring. Planting under shelterwood can also help protect the seedlings from spring frost damages. As similar results for bud development patterns of Douglas fir and Norway spruce provenances were obtained from the greenhouse and field trials, greenhouse tests could facilitate selection of provenances.

  • 14.
    Nilsson, Börje
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Mathematics and Systems Engineering.
    Sjödén, Therese
    Växjö University, Faculty of Mathematics/Science/Technology, School of Mathematics and Systems Engineering.
    Nordebo, Sven
    Växjö University, Faculty of Mathematics/Science/Technology, School of Mathematics and Systems Engineering.
    Säll, Harald
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    A method for under bark detection of the wood grain angle radial dependence2007In: Wood Material Science and Engineering, ISSN 1748-0272, Vol. 2, no 3,4, p. 118-129Article in journal (Refereed)
    Abstract [en]

    Twist in wood, being closely related to spiral grain, may cause

    serious problems in building structures, furniture, and joinery. It is therefore of great interest to sort out, at an early stage in the manufacturing process, trees, logs and boards that have an access of spiral grain. The spiral grain pattern is described by a helical deviation of the fibre direction in relation to the longitudinal direction of a living tree or a log and seems to be an indicator for other defects such as compression wood. Remote microwave sensing of spiral grain has received a large interest during the latest two decades. Its development has been impeded by the large variation with moisture content of the microwave properties of wood and by the complexity in modelling the electromagnetic field in a log with spiral grain. A review is presented of a direct method with no requirement of information on moisture content for boards. This procedure has recently been generalized to cylindrical logs and trees having a constant slope of the grain. A further generalization is presented here to allow for the normal spiral grain pattern with radially changing slope of grain in wood under bark. Based on this theory, a measurement procedure is proposed for the detection of wood grain angle with radial dependence, requiring no information on moisture content in the sapwood, also applicable for completely or partially frozen wood. A suitable application would be an instrument to use in the forest for measurements on living trees or logs.

  • 15.
    Phiri, Darius
    et al.
    Univ Stellenbosch, South Africa.
    Ackerman, Pierre
    Univ Stellenbosch, South Africa.
    Wessels, Brand
    Univ Stellenbosch, South Africa.
    du Toit, Ben
    Univ Stellenbosch, South Africa.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Lundqvist, Sven-Olof
    Innventia AB, Wood & Fibre Measurement Lab, Stockholm.
    Seifert, Thomas
    Univ Stellenbosch, South Africa.
    Biomass equations for selected drought-tolerant eucalypts in South Africa2015In: Southern Forests, a journal of forest science, ISSN 2070-2620, E-ISSN 2070-2639, Vol. 77, no 4, p. 255-262Article in journal (Refereed)
    Abstract [en]

    In the water-scarce environment of South Africa, drought-tolerant eucalypt species have the potential to contribute to the timber and biomass resource. Biomass functions are a necessary prerequisite to predict yield and carbon sequestration. In this study preliminary biomass models for Eucalyptus cladocalyx, E. gomphocephala and E. grandis x E. camaldulensis from the dry West Coast of South Africa were developed. The study was based on 33 trees, which were destructively sampled for biomass components (branchwood, stems, bark and foliage). Simultaneous regression equations based on seemingly unrelated regression were fitted to estimate biomass while ensuring additivity. Models were of the classical allometric form, ln(Y) = a+x(1)ln(dbh)+x(2)ln(h), of which the best models explained between 70% and 98% of the variation of the predicted biomass quantities. A general model for the pooled data of all species showed a good fit as well as robust model behaviour. The average biomass proportions of the stemwood, bark, branches and foliage were 60%, 6%, 29% and 5%, respectively.

  • 16.
    Säll, Harald
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Spiral Grain in Norway Spruce2002Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Wood is a major construction material that is used in many contexts, and for different purposes. Serious problems may arise, however, when moisture related deformations as twist occur in wood used in different types of building structures, joinery and furniture. Twist can be explained to a great degree by the helical deviation of the grain angle in relation to the longitudinal direction of the log or the sawn board. Wood fibres form a spiral within the tree, and this is a natural occurrence that is named spiral grain. The wood fibres close to the pith in Norway spruce form a left-handed spiral. In most trees the grain angle turns over to be right-handed with time. Sawn timber that exhibits large grain angles lead to problems of shape stability and stiffness in finished constructions. In this thesis the spiral grain in Norway spruce (Picea abies (L.) Karst.) was stated as well as the effect on sawn timber.

    The material was based on sample trees from Sweden and Finland. Samples were taken in twenty-two stands at different heights in tree. From six stands studs were sawn and dried for measuring twist and other deformations. The spiral grain was measured with the method scribe test on 390 log discs taken at the top-end of the logs. Account was given concerning changes in grain angle from pith to bark, regarding both increasing annual ring numbers and distance from pith. The development of grain angle over tree age was utilized to study whether annual growth, size of tree, height in tree as well as silvicultural treatments affected spiral grain. Moreover, the relation between grain angle and distance to pith (in mm) was used to forecast twist in sawn timber.

    The left-handed grain angle was at its greatest between the fourth and eighth annual rings. Thereafter for most trees the grain angle turned from left-handed to right-handed in a linear fashion, in a manner that was unique for each individual tree. The pattern of spiral grain differed significantly between different stands, regarding change of inclination with increasing age or distance from pith. The culmination of the grain angle close to the pith occurred at somewhat higher age higher up in the trunk. The grain angle decreased faster in top logs than it did in the butt logs. The largest trees within a stand had a grain angle that turned to right in a slower way than smaller ones. The thinning strength and type of thinning regime also affected the character of spiral grain in the remaining trees in a stand. There was an indication that strong thinnings, where fast growing trees are retained, may lead to more individuals in a stand that exhibit high grain angles under bark.

    With knowledge of the size and direction of the grain angle under bark, and the diameter of the log, calculations can be made that show how twisted the sawn timber will be after drying. This can be used for deciding whether an individual log can profitably be sawn and processed further or not. The grain angle under bark can be used to remove trees showing the greatest degree of spiral grain already in the first thinning. Silvicultural methods aiming at even and dense Norway spruce stands, which normally is practised in Scandinavia, will probably result in timber with relatively low risk concerning large grain angle and subsequent risk for twist in sawn wood.

  • 17.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Spiral grain in trees from drought tolerant Eucalyptus species grown on dry land on the west coast of South Africa2015In: Collection of Extended abstractsfor the International Symposium: Silviculture and Management of Dryland Forests, Stellenbosch, South Africa,16-19 March 2015, Stellenbosch University , 2015, p. 87-89Conference paper (Refereed)
    Abstract [en]

    In this project titled “Evaluation of drought resistant tree species to alleviate poverty in arid regions of South Africa” trees from a 20-year old field trial from two sites on the dry west coast area of South Africa were recently evaluated for growth characteristics. The three most promising Eucalyptus species, namely E. gomphocephala, E. cladocalyx and E. grandis × camaldulensis hybrid, for growth characteristics were selected for further evaluation. The objective of the study reported was to investigate between species variability of selected physical and processing properties determining the suitability of these three species for lumber production. It will also be useful for informing tree breeders and silviculturists to identify which properties need improvement through breeding selection or forest management strategies. And in the future results can hopefully be used for selection of species for small farm plantations which may be processed and sold to generate income.

    One of most common reasons for a customer to avoid using wood is the lack of shape stability. There is a clear connection between spiral growth and how twisted the sawn timber will be when it is dried. Depending on the log diameter a grain angle over 3 to 5 degrees will produce sawn wood that will be pronounced to twist. In older softwood trees, the cracks lean mostly to the right. This means that the grain angle is right handed, and the visible cracks create a spiral in an anti-clockwise direction, looking from the base to the top of the tree (Figure 1). In spruce trees, however, the grain angle close to the pith is left-handed, which means that the fibres follow a clockwise spiral up the trunk (Harris 1989).

  • 18.
    Säll, Harald
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Dahlblom, OlaLund University.
    Silviculture Influence on Spiral Grain in Norway Spruce1999Conference proceedings (editor) (Other academic)
    Abstract [en]

    In the present investigation a significant variation of spiral grain with annual ring number as well as with height in stem was observed. It was also observed that the spiral grain may be significantly different in stands with different site conditions and silvicultural treatment. It will however require further research to gain knowledge about to what extent differences in spiral grain in different stands are due to site conditions and to what extent they are due to silvicultural treatment. In addition to site conditions and silvicultural treatment the development of spiral grain may be affected by the genetics of the trees.

  • 19.
    Säll, Harald
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Skog och trä.
    Källsner, Bo
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Skog och trä.
    Olsson, Anders
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Bending strength and stiffness of aspen sawn timber2007In: Quality Control for Wood and Wood Products, COST, Warsaw , 2007, p. 6-Conference paper (Refereed)
    Abstract [en]

    In order to investigate the possibility of using sawn timber of European aspen (Populus tremula L.) as a structural

    material, 150 pieces of the dimension 45 x 120 mm2 were selected from a sawmill in the south of Sweden. The material was

    visually strength graded using the Nordic standard INSTA 142 and the British standard BS 4978-1996, respectively.

    The timber pieces were also subjected to flat-wise bending in a Cook-Bolinder Ò strength grading machine. Finally all

    specimens were tested in edge-wise bending according to the European testing standard EN 408. Global and local moduli

    of elasticity as well as bending strength were determined.

    The results indicate that the visual grading rules, intended for use on Norway spruce and Scots pine, seem to work fairly

    well on European aspen. However, grading in a flat-wise bending machine like the Cook-Bolinder seems to give a lower

    correlation between stiffness and strength for aspen timber than generally found for coniferous. Further, the correlation

    between density and bending strength was found to be very low for the aspen timber tested. It was also noticed that

    the aspen timber has a slightly higher bending strength and modulus of elasticity than is the case for normal qualities

    of Norway spruce.

    The study indicates that sawn timber of European aspen grown in southern Sweden can be visually graded and used

    as structural material.

  • 20.
    Wessels, CB
    et al.
    University of Stellenbosch, South Africa.
    Crafford, PL
    University of Stellenbosch, South Africa .
    du Toit, B
    University of Stellenbosch, South Africa.
    Grahn, T
    Innventia, Sweden.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Lundqvist, S-O
    Innventia, Sweden.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Seifert, T
    Univesity of Stellenbosch, South Africa.
    Lumber properties of three drought tolerant eucalyptus species grown in arid regions of south africa2015In: IUFRO Symposium: Silviculture and Management of Dryland Forests,, 2015Conference paper (Other academic)
  • 21.
    Wessels, CB
    et al.
    University of Stellenbosch, South Africa.
    Crafford, PL
    University of Stellenbosch, South Africa.
    DuToit, B
    University of Stellenbosch, South Africa.
    Grahn, T
    Innventia AB, Stockholm.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Lundqvist, S-O
    Innventia AB, Stockholm.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Seifert, Thomas
    University of Stellenbosch, South Africa.
    Variation in physical and mechanical properties from three drought tolerant Eucalyptus species grown on the dry west coast of Southern Africa2016In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 74, no 4, p. 563-575Article in journal (Refereed)
    Abstract [en]

    Southern Africa, and specifically its western parts is dominated by low rainfall areas, and it is expected that the rainfall in most of these parts will in future decrease further due to climate change. Woodlots of fast-growing, non-invasive tree species can provide the opportunity to produce wood and release the pressure on natural woodlands, while creating much needed income to inhabitants. Over the last two decades several trials of Eucalyptus species that could potentially withstand arid conditions were established on the South African west coast. The three most promising genotypes according to their volume growth were selected among 46 pure and hybrid species from two 20-year-old trials for further evaluation. These included 10 Eucalyptus grandis × Eucalyptus camaldulensis hybrid trees, 9 Eucalyptus gomphocephala trees, and 9Eucalyptus cladocalyx trees for a total of 28 trees. The objective of the study reported here was to investigate the within-tree and between species variability of selected physical and processing properties determining the suitability of these three species for lumber production. The density, microfibril angle, spiral grain angle, MOE, MOR, radial and tangential shrinkage, twist, bow, splitting, and collapse were measured in a radial and longitudinal gradient. Valuable insights were gained which could provide decision support for planting, processing and further research on these species when grown in arid conditions. The E. grandis × camaldulensis hybrid was inferior in terms of most relevant properties to the other two species evaluated. The main shortcoming of both E. gomphocephala and E. cladocalyx was the high levels of twist in lumber.

1 - 21 of 21
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