Dendrochronologists have used the presence of spiral grain as an indicator of old trees for most of the history of the field, although this relationship has been little studied. We examined cross-sections from dead trees and used a 12-mm Haglof Swedish Increment borer to collect cores from living white oak (Quercus alba L.) trees in an Eastern Deciduous Forest stand in southwestern Illinois. Spiral grain is the alignment of wood fibers to the longitudinal axis of trees and is driven by patterns of initial cambial cell division. In this study, we examine environmental factors that may affect spiral grain severity, the usefulness of non-destructive sampling methods (using the 12-mm increment borer), and the relationship between tree age and spiral grain. We tested Brazier’s method (1965) of averaging the spiral grain angle from two radii taken 180 degrees apart (i.e. one diameter in the tree) to get representative grain angles for the whole circumference of a tree at a certain height. The 12-mm increment borer did not produce consistent results in this study; therefore, the collection of cross-sections is advised for the study of spiral grain in white oaks. Brazier’s method should not be used in white oaks and should not be applied universally to all tree species. The severity of spiral grain is expressed in the xylem and may not be expressed in the bark of the tree. Left spiral grain does generally increase in white oaks with age, although this relationship is not always consistent, so a tree without severe spiral grain is not necessarily young.

Radiata pine (Pinus radiata) is the most important plantation tree in New Zealand forestry, and factors that reduce the quality of wood cause significant economic loss. Two of the most important of these issues are compression wood and spiral grain. Compression wood is a type of reaction wood, formed when a tree moves away from the vertical, and is characterised by biochemical and structural changes within the wood that reduce its quality and value. Spiral grain, however, is the alignment of the wood grain in a helix around the tree’s axis and away from the vertical. Again, this reduces the structural qualities of the wood and thus its value. Spiral grain and compression wood are notorious for their deleterious effect on the quality of wood produced and are very important for the forest industry due to the huge economic loss they cause. The demand for reliable tools to evaluate these wood quality issues in clonal planting material at an early stage, within 3 years of germination rather than at 8 to 15 years as in current practise, is of ever increasing importance from plant breeders and other industry stake holders. Therefore this research was undertaken with an overall aim to develop quick, easy and reproducible techniques to evaluate young radiata pine clones (up to 3 years old) based on compression wood content and presence of spiral grain. This is important because a shortened breeding cycle could provide significant economic benefits to the forest industry. The incidence of these commercially important wood quality parameters has been studied in this thesis in research conducted on young trees (1 to 3 years old). The research described in this thesis used a variety of different imaging approaches to investigate wood structure, including polarised light and confocal microscopy, and X-ray tomography and circular polarised light scanning. The images achieved have been analysed using a range of different software, including Photoshop, ImageJ and Matlab bringing a quantification approach to the imaging. Compression wood was quantified in young clonal material using images collected with a commercial document scanner, and processed using image analysis tools available in Photoshop. An easy, reliable and robust, automatic image analysis protocol was successfully developed and tested for the detection and quantification of compression wood in these young trees. This new technique to detect and quantify compression wood was based on the thresholding of the blue channel of the scanned RGB image as this was demonstrated to contain the greatest image contrast. Development of this new technique may reduce the waiting time for screening clonal planting materials based on compression wood content. To understand the organisation of the grain at a cellular level within these young trees, confocal microscopy techniques were utilised. The cell wall characteristics and fluorescence properties of compression wood in comparison with normal wood were investigated using a new cellulose specific dye, pontamine fast scarlet 4B. Staining protocols for this dye for confocal microscopy were optimised, and the potential of measuring the microfibril angle of the S1 and S3 layers of the pontamine treated opposite wood was demonstrated through either direct observations of these layers, or through the property of bifluorescence where the dye is excited only when aligned parallel to the polarisation of the incident light. Despite extensive work with confocal microscopy, this technique proved to be unsuitable for investigations of spiral grain because although it provided cellular detail, imaging was limited to the surface layers of sections, and the area over which observations were required was prohibitive. Instead of confocal microscopy, the incidence of spiral grain in young stems was investigated in two completely new ways. Resin canals, which are formed from the same cambial initials as the tracheids and which align with the grain, were used as a proxy to demonstrate the grain changes. A novel technique, using circular polarised light and a professional flatbed scanner, was developed to image whole serial transverse sections of the young stems to detect the resin canals. Using ImageJ, the number and location of resin canals was measured on vertical controls, and trees that had been rocked and leaned. The number and frequency of resin canals were less in tilted trees, especially in compression wood, compared to the higher number of canals formed in the rocked trees. More importantly, a combination of serial sectioning and this approach allowed a 3-dimensional view of the orientation of resin canals inside a stem to be generated with ImageJ, and the angles of these canals could be measured using Matlab. The resin canals were oriented with a left-handed spiralling near the stem surface whereas the canals near to the pith were nearly straight, consistent with previous observations of the development of spiral grain in radiata pine. However, it was observed that while vertical trees had a symmetric pattern of grain and grain changes around the stem, this was not the case in tilted trees. In these, the opposite wood often had severe spiral grain visible through formation of twist whereas the compression wood formed on the lower side had bending. Consistent with this, grain associated with compression wood was significantly straighter than in opposite wood. This hitherto unknown link between the incidence of compression wood and spiral grain was investigated and explained on the basis of the characteristics of resin canals in these types of wood. X-ray micro-tomography was also used to investigate resin canals in the stubs from which serial sections were collected. The 3D reconstructions of the resin canals showed exactly the same patterns as observed by polarised light scanning.

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.