Genetic parameters for grain angle in 28-year-old Norway spruce progeny trials and their parent seed orchard

? Sawn wood which acquires twist during drying is a substantial problem for the sawmill industry and is to a large extent caused by spiralled grain in the tree.

? In this study, the feasibility of using spiral grain angles as a selection trait in Norway spruce (Picea abies (L.) Karst) tree breeding and the extent of grain angle and its breeding values were investigated. Grain angles under bark and diameter were measured at breast height in three 28-year-old Norway spruce progeny trials and in their parent seed orchard.

? The mean grain angle value was 1.76° in the progeny trials and 1.84° in the seed orchard. Estimated genetic standard deviations for grain angle were almost 1°. Progeny trial heritabilities (H ² > 0.3) were larger than the seed orchard heritability (H ² = 0.24). Genotype by environment interaction among the progeny trials was negligible for grain angle. Progeny trial grain angles exhibited genetic correlation with seed orchard grain angles in the range 0.66 to 0.84.

? Thus, mature wood grain angles are also under considerable genetic control, raising the opportunity to reduce the occurence of left-grained trees, which are prone to producing twisted wood.

     

Rotational position of curved saw logs and warp of the sawn timber

With the development of scanning technology in sawmills, it is possible to optimise log rotational position when sawing. However, choosing a different rotational position than horns down might be detrimental for the board shape after drying, especially for curved logs. Thus, there is a need to investigate at what level of log curve it is possible to freely rotate logs without causing board warp. This study was carried out through a test sawing that was conducted at a sawmill situated in the middle of Sweden. The tests were made on 177 Norway spruce logs, with varying amount of curve. Half of the logs were sawn in the horns-down position, half were sawn rotated perpendicular to horns down. Log shape and warp of the dried boards were measured. The results indicated a relationship between board spring, log curve and choice of rotational position. Furthermore, board bow was related to log curve but not rotational position. It can be concluded that for straight logs, with a bow height of less than 15 mm, an unconventional rotational position does not cause excess spring in the boards. Bow and twist are not affected by the rotational position at all.     

Geometric model to predict twist in unrestrained boards

A theory has been developed for calculating the twist that develops in boards during drying without restraint, as well as the deformation in cross-section that accompanies the development of twist. Calculations require a knowledge of only a limited number of parameters: width, thickness and length of the board, annual ring orientation, distance from the pith, radial, tangential and longitudinal shrinkage coefficients, and the variation of spiral grain angle (SGA) with distance from the pith. The theory is derived from geometrical and physical principles and shows that a complicated interaction between all the above parameters gives rise to twist. A novel coordinate system is used that is better adapted to the fact that spiral grain lies at an angle to the log axis rather than the usual Cartesian or cylindrical polar coordinates. Unlike the finite element models that have recently been developed this theory does not allow for the effect of stresses that develop in a board, although the theory in its present form can easily be extended to incorporate this effect. The advantage of this theory over the more exact finite element models lies in its educational value in that it clearly identifies the mechanisms that are responsible for twist. An associated MS Excel spreadsheet allows rapid analysis of different scenarios such as the effect on twist of changing the shrinkage coefficients, annual ring orientations and moisture content. The theory predicts that for radiata pine 100×50 mm boards maximum twist occurs near the pith, and that the direction of twist reverses when the distance from the pith is greater than about 120 mm. These predictions are shown to agree with experiment. The theory also predicts that if a radiata pine log is live-sawn (through-and-through sawn) there will be two regions in the mature wood where the quartersawn boards will have large negative twist values, but that this can be avoided by cant- or grade-sawing. In contrast, the theory also predicts that if the SGA is constant at 4° from pith to bark, board twist will decrease smoothly from pith to bark for all annual ring orientations without ever becoming negative.     

Genetic variation and relationships to growth traits for microfibril angle,wood density and modulus of elasticity in a Picea abies clonal trial in southern Sweden

Abstract

Genetic variation in wood density, microfibril angle (MFA), wood stiffness (MOE), height, diameter and volume was investigated in a 26-year-old Norway spruce [(Picea abies (L.) Karst.] clonal trial in southern Sweden. Wood quality measurements were performed on 10 mm increment cores using SilviScan. For MFA, mean values of annual rings showed the highest value (30°) at ring 2 counting from the pith, followed by a steep decrease and a gradual stabilization around ring 12 at approximately 14°. MOE showed a monotonic increase from 5 GPa to 14 GPa when moving from pith to bark. High broad-sense heritability values were found for wood density (0.48), MFA (0.41) and MOE (0.50). All growth traits displayed heritability values of similar magnitudes as reported in earlier studies. The generally high age–age correlations between different sections of the wood cores suggested that early selection for wood quality traits would be successful. Owing to unfavorable genetic correlations between volume and MOE, the correlated response indicated that selection for volume only at age 10 would result in a 0.27% decrease in weighted MOE at age 26 for every 1% increase in volume.     

Early selection for resistance to <Emphasis Type="Italic">Heterobasidion parviporum</Emphasis> in Norway spruce is not likely to adversely affect growth and wood quality traits in late-age performance

Infections with Heterobasidion parviporum devalue the Norway spruce timber as the decayed wood does not meet the necessary quality requirements for sawing. To evaluate the incorporation of disease resistance in the Norway spruce breeding strategy, an inoculation experiment with H. parviporum on 2-year-old progenies of 466 open-pollinated families was conducted under greenhouse (nursery) conditions. Lesion length in the phloem (LL), fungal growth in sapwood (FG) and growth (D) were measured on an average of 10 seedlings for each family. The genetic variation and genetic correlations between both LL, FG and growth in the nursery trial and wood quality traits measured previously from 21-year old trees in two progeny trials, including solid-wood quality traits (wood density, and modulus of elasticity) and fiber properties traits (radial fiber width, tangential fiber width, fiber wall thickness, fiber coarseness, microfibril angle and fiber length). For both LL and FG, large coefficients of phenotypic variation (>?26%) and genetic variation (>?46%) were detected. Heritabilities of LL and FG were 0.33 and 0.42, respectively. We found no significant correlations between wood quality traits and growth in the field progeny trials with neither LL nor FG in the nursery trial. Our data suggest that the genetic gains may reach 41 and 52% from mass selection by LL and FG, respectively. Early selection for resistance to H. parviporum based on assessments of fungal spread in the sapwood in nursery material, FG, will not adversely affect growth and wood quality traits in late-age performance.     

Influence of growth stresses and material properties on distortion of sawn timber — numerical investigation

? The board distortion that occurs during the sawing and the drying process causes major problems in the utilisation of sawn timber. The distortion is highly influenced by parameters such as spiral grain angle, modulus of elasticity, shrinkage, growth stresses and sawing pattern.

? In this study a finite element simulation of log sawing and timber drying was performed to study how these parameters interact to affect board distortion. A total of 81 logs with different material combinations were simulated. From each simulated log four boards with different annual ring orientation were studied.

? The results showed that the elastic modulus, shrinkage coefficient and growth stresses had a large influence on the final bow and spring deformation. After sawing of the log into boards, the release of growth stresses was the main contributor to the bow and spring deformation. For boards with low modulus of elasticity, the bending distortion became larger than for the boards with high modulus of elasticity. The twist deformation was very small after sawing but increased significantly during drying of the boards. The results showed that spiral grain angle and the board location within the log were the main contributors to the twist deformation.

     

Measurement of spiral grain with computed tomography

Spiral grain is a feature of wood that affects the shape of the sawn timber. Boards sawn from logs with a large spiral grain have a tendency to twist when the moisture content changes. In sawmills the spiral grain in logs is judged manually. For research purposes the spiral grain in stems and logs is normally measured by destructive methods. In this study the spiral grain of the stems was measured nondestructively with a computed tomography (CT) scanner. Twelve Norway spruce (Picea abies) stems from two stands in Sweden were scanned with a CT scanner with one cross-sectional scan every 10mm along the stem. Concentric surfaces at various distances from the pith were reconstructed from the stack of CT images. In these concentric-surface images, which show various internal features of the log. the spiral grain angle was measured at different distances from the pith and at different heights in the stem. The destructive measurements of the spiral grain were carried out on disks from the top ends of the logs. On these disks the spiral grain was measured at different distances from the pith with a protractor. Finally, the results from the destructive method were compared with the results from analysis of the CT images. The nondestructive and destructive measurements were compared in pairs with the same radial and approximately the same height position in each pair. The correlations (r) between the two methods were 0.81 and 0.71. respectively, for the two stands. It was concluded that it is possible to measure the spiral grain angle nondestructively with a CT scanner.An outline of this study was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto     

Genetic parameters of growth and wood quality traits in Picea abies

Genetic parameters were estimated for wood and growth traits in two 19-yr-old clonal trials and a 40-yr-old full-sib progeny trial of Norway spruce [Picea abies (L.) Karst.]. In the clonal trials high (>0.4) broad-sense heritabilities were found for wood density traits, lignin content, number of internal cracks, growth traits, spiral grain and number of resin canals. Moderate (0.2–0.4) heritabilities were found for tracheid lumen diameter and cell wall thickness, microfibril angle and tracheid length, while low heritabilities (<0.2) were found for pulp yield, fibre strength, wood stiffness and wood colour. Lignin content and pulp yield showed low genetic variation, whereas the genotypic coefficient of variation for most other traits ranged between 5 and 15%. Most traits showed low levels of genotype by environment interaction. Among the wood properties, latewood proportion, earlywood density and ring density showed significant, adverse correlations with volume in both clonal trials.     

Finite element study of growth stress formation in wood and related distortion of sawn timber

Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain.     

Predicting spiral grain by computed tomography of Norway spruce

Spiral grain is a feature of wood that affects the shape of the sawn timber. Boards sawn from logs with a large spiral grain have a tendency to twist when the moisture content changes. The aim of this study was to investigate the possibility of predicting spiral grain based on variables that should be measurable with an X-ray LogScanner. The study was based on 49 Norway spruce (Picea abies) logs from three stands in Sweden. The logs were scanned with a computed tomography (CT) scanner every 10mm along the log. Concentric surfaces at various distances from the pith were then reconstructed from the stack of CT images. The spiral grain angle was measured in these concentric surface images, and a statistical model for predicting spiral grain was calibrated using partial least squares (PLS) regression. The PLS model predicts the spiral grain of a log at a distance 50mm from the pith based on different variables that should be measurable with an industrial X-ray LogScanner. The result was a PLS model withR ²=0.52 for the training set andR ²=0.37 for the test set. We concluded that it should be possible to predict the spiral grain of a log based on variables measured by an industrial X-ray LogScanner. The most important variables for predicting spiral grain were measures of sapwood content, variation in the ratio between the heartwood and log areas, and the standard deviation for the mean log density in 10mm thick cross slices along the log. The accuracy when sorting the logs into two groups with spiral grain of 2.0° and of <2.0°, respectively, was 84% of the correctly sorted logs.     

Radial variations of wood properties of an endangered species, <Emphasis Type="Italic">Pinus armandii</Emphasis> var. <Emphasis Type="Italic">amamiana</Emphasis>

A dead tree of Pinus armandii Franch. var. amamiana (Koidz.) Hatusima (abbreviated to PAAm) was obtained from a natural habitat on Tanega-shima Island and various properties of its wood were investigated. Grain angle was measured and soft X-ray analysis was undertaken to obtain the density in each annual ring. Unit shrinkage and dynamic properties were measured by shrinkage, bending, and compression tests. Variations of wood properties in the radial direction, relationships of wood properties to density, and annual ring width were examined. Roughly speaking, variations in the radial direction of the grain angle, twist angle by drying, Young’s modulus and strength in static bending, absorbed energy in impact bending, compressive Young’s modulus, compressive strength, and compressive proportional limit corresponded to the variation of annual ring width. As a result, it was determined that if PAAm is afforested artificially for the purposes of lumber production and conservation, the annual rings of logs should not be too widely spaced. Wood properties of PAAm were similar to those of Japanese black pine (Pinus thunbergii Parl.), which is another representative pine on Tanegashima Island. This study was presented in part at the 56th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007     

Classification of Picea abies Pulpwood According to Wood and Stand Properties

Different classification systems for Norway spruce (Picea abies (L.) Karst.) pulpwood were compared. The classification systems were applied on truckloads or single logs in southern Sweden. Truckload classification according to mean annual growth ring width gave better separation of the wood properties basic density, juvenile wood and dry matter content, than classification according to harvest type (first thinning, later thinning or final felling). The assortments did not have significantly different wood brightness. Sorting at log level according to diameter, mean annual growth ring width or number of annual growth rings, which could be done at harvesting, did not drastically improve differentiation of the mean values of the wood properties or reduce variance compared to truckload classification. The variation in wood properties within assortments remained large owing to the large variation in wood properties between and within logs. Substantial reduction in dry matter variation could be achieved by truckload classification during the summer.     

Schnittholzqualität und Furniereignung von Douglasien aus linksrheinischen Anbaugebieten

Summary Douglas fir sample trees from 9 various stands were cut in sawmills. Every board of the converted timber was graded; all defects in timber were analysed, especially all black and sound knots on the surface of the boards were measured. The percentage of good boards prooved to be comparatively low. From fertile sites the sawn timber quality seems to be inferior compared with wood from poorer and dryer sites. Douglas firs grown single between broadleaved stands showed the lowest timber quality. Throughout the quantity and thickness of black knots were responsible for poor quality. Experiments with production of veneer yielded useful carved veneers when sliced of quartered and clear logs. Branchless logs from 80 years old Douglas firs could be worked up to carved veneers, but are too young for peeled veneers. For full veneer logs diameters of 70 cm and structure of small annual rings is essential. For saw timber as well as for veneerwood production short rotation below 120 years is not suitable. Moreover pruning is necessary.      

Outdoor exposure of untreated Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.] wood samples

Abstract

Untreated Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) samples were exposed above ground in a durability test for 6 years. The samples consisted of three pieces of wood, 22×95×500 mm, screwed together; two pieces lengthwise with a third piece overlapping. Weight was measured, to calculate moisture content (MC), and samples checked regularly for cracks and fungal growth. Parameters investigated were heartwood/sapwood (pine), annual ring orientation (spruce), stand site, annual ring width and density. Stand site, annual ring width and density had no influence on MC or fungal growth for either pine or spruce. Spruce samples with vertical annual rings had fewer cracks than samples with horizontal annual rings. Pine sapwood samples had a high MC and a large amount of rot fungi, while heartwood had a lower MC and no rot. Most spruce samples were similar to pine heartwood, except from a few samples that had high MC and fungal growth. Those were all sawn from the outer part of the log. Therefore, it can be stated that spruce sawn from the inner part has almost the same properties as pine heartwood, while spruce from the outer part of the log has similar properties to pine sapwood.     

Indented rings (hazel growth) of Norway spruce reduce anisotropy of mechanical properties

This study presents three-point bending test results of Norway spruce clear wood specimens loaded on the radial-longitudinal plane in two different load cases. The tested samples were graded as resonance wood for instrument making and were characterised by narrow annual rings and relatively low density. The modulus of elasticity (MOE) and the corresponding modulus of rupture (MOR) are illustrated separately for the samples with straight grain and the group showing the specific growth pattern of indented rings (‘hazel growth’). With the longitudinal wood anatomical direction parallel to span width, the fibre deviation caused by the indents reduces MOE and MOR values, whereas a ‘reinforcing’ effect of the indents could be observed for the load case with span width parallel to the radial direction. Both aspects lead to a reduction in anisotropy for hazel-growth Norway spruce (anisotropy MOE: indented rings 11.6, straight grain 14.7, anisotropy MOR: indented rings 6.9, straight grain 8.9), which partly explains the exceptional position of this growth pattern for the construction of high-class musical instruments with outstanding mechanical and acoustical performance.     

Genetic correlations among juvenile wood quality and growth traits and implications for selection strategy in Pinus radiata D. Don

? Juvenile wood quality in Pinus radiata is affected by factors such as low density, stiffness, and high microfibril angle, spiral grain, and shrinkage. Adverse genetic correlations between growth and wood quality traits remain as one of the main constraints in radiata pine advanced generation selection breeding program.

? Juvenile wood property data for this study were available from two progeny tests aged 7 and 6 y. We estimated the genetic correlations between stiffness, density, microfibril angle, spiral grain, shrinkage in the juvenile core and DBH growth in radiata pine, and) to evaluated various selection scenarios to deal with multiple objective traits.

? Negative genetic correlations were found for modulus of elasticity (MoE) and density with microfibril angle, spiral grain, shrinkage, and DBH. We observed low to moderate unfavourable genetic correlations between all wood quality traits and DBH growth.

? These low to moderate genetic correlations suggest that there may be some genotypes which have high DBH growth performance while also having high wood stiffness and density, and that the adverse correlation between DBH and MoE may not entirely prohibit the improvement of both traits. Results indicate that, in the short term, the optimal strategy is index selection using economic weights for breeding objective traits (MAI and stiffness) in radiata pine.

? In the long-term, simultaneously purging of the adverse genetic correlation and optimizing index selection may be the best selection strategy in multiple-trait selection breeding programs with adverse genetic correlations.

     

Variation in wood properties among five full-sib families of Norway spruce (Picea abies)

Genetic- and environmental variation and correlation patterns were characterized for modulus of elasticity (MOE), modulus of rupture (MOR) and related wood traits: latewood proportion, wood density, spiral grain, microfibril angle and lignin content in five full-sib families of Norway spruce. The families were evaluated on the basis of clearwood specimens from the juvenile -mature wood transition zone of 93 sampled trees at age 30 year from seed. Family-means varied significantly (p < 0.05) for all wood traits studied except lignin content. MOE varied between 7.9–14.1 GPa among trees and 9.4–11.0 GPa among families. MOR varied between 47–87 MPa among trees and 61–71 MPa among families. Families remained significantly different in an analysis of specific MOE (MOE/density) and MOR (MOR/density). Hence, solely relying on wood density as a wood quality trait in tree breeding would not fully yield the potential genetic gain for MOE and MOR. Correlations between wood structural traits and specific MOE and MOR are presented and discussed.     

Optimization potential for perception-oriented appearance classification by simulated sawing of computed tomography-scanned logs of Norway spruce

Abstract

Wood, as a natural material, has favourable properties in both technical and aesthetic aspects. Due to its inherent variability, production of high-quality sawn timber demands adequate control of log conversion, which is feasible with computed tomography (CT) log scanning. Existing appearance grading rules for sawn timber might not fully reflect people's visual perception of wood surfaces, and therefore, an alternative, more perception-oriented appearance classification could be beneficial. An appearance classification of sawn timber based on partial least squares discriminant analysis (PLS-DA) of knot-pattern variables was developed and tested. Knot-pattern variables derived from images of board faces were used in training PLS-DA models against an initial classification of the board faces previously established by aid of cluster analysis. Virtual board faces obtained from simulated breakdown of 57 CT-scanned Norway spruce logs were graded according to the developed classification. Visual assessment of the grading results indicated that the classification was largely consistent with human perception of board appearance. An initial estimation of the potential to optimize log rotation, based on CT data, for the established appearance grades was derived from the simulations. Considerable potential to increase the yield of a desired appearance grade, compared to conventional log positioning, was observed.     

Choosing green sawing dimensions for Norway spruce from stochastic simulations

The high accuracy of log positioning and the stability of saw blades in breakdown machinery in modern sawmills have reduced the need to add margins for sawing variations. Oversize green sawing dimensions are still needed, but mainly to allow for drying shrinkage. This has put a new focus on better adapting green sawing dimensions to the shrinkage behavior of wood. In this study, a method for optimization of green sawing dimensions using stochastic simulation is presented. Normal distributions were generated for planed dry dimensions, kerf width, and target moisture content. The minimum share of boards exceeding the specified dry dimensions was decided, and deformations in boards from all positions in the cross section in a number of logs were simulated. The simulated shrinkage allowance from stochastic simulations was compared to experimental results from an industry test and to finite element results based on material data for Norway spruce. The results showed that the green width of the sawn boards should increase when the number of boards in the center yield increases. The green thickness of boards should be thinner for center boards and outer boards than for inner boards.     

Comparing predictability of board strength between computed tomography,discrete X-ray,and 3D scanning of Norway spruce logs

Strength graded boards of Norway spruce (Picea abies (L.) Karst.) are important products for many Scandinavian sawmills. If the bending strength of the produced boards can be predicted before sawing the logs, the raw material can be used more efficiently. In previous studies it is shown that the bending strength can be predicted to some extent using discrete X-ray scanning of logs. In this study, we have evaluated if it is possible to predict bending strength of Norway spruce boards with higher accuracy using computed tomography (CT) scanning of logs compared to a combination of discrete X-ray and 3D scanning. The method was to construct multivariate models of bending strength for three different board dimensions. Our results showed that CT scanning of logs produces better models of bending strength compared to a combination of discrete X-ray and 3D scanning. The main reason for this difference was the benefit of knowing the position of where the boards were cut from the logs and therefore detailed knot information could be used in the prediction models. Due to the small number of observations in this study, care should be taken when comparing the resulting prediction models to results from other studies.