Assessing Spiral Grain Angle by Light Transmission: – Proof of Concept –

Spiral grain measurements are subject to a high degree of variation and interpretation, depending on the assessment method used. A new measurement approach was tested whereby light was directed through disc samples on a flatbed scanner and the deviation along the grain assessed by means of a template to allow the mapping of grain angle variation radially and tangentially within discs. Initial results showed that the approach was valid for green discs up to 35 mm thick and small enough to fit on an A4 scanner. Comparisons with traditional scribing and cleaving methods were favourable, indicating that the light transmission approach could allow much faster and more accurate data acquisition. The possibility of using larger discs would enhance the ability to assess spatial variation in grain angle and minimise the effects of sample reference geometry with respect to the tree axis (disc tilt and parallax). Further work may also be required to ensure that reliable spiral grain values are obtained from both sapwood and heartwood. The ultimate goal is to develop an automated system for reconstructing stem characteristics from measurements on large fresh green discs to enable the 3-dimensional mapping of individual stem variations in key wood properties and modelling the impacts of silviculture and genetics on wood products.

Variation in wood structure of white fir along an elevational transect

Several wood structural characteristics were measured in 15-year-old Abiesconcolor (white fir) from four populations along an elevational transect in the central Sierra Nevada region. The trees had been growing in a plantation near Placerville, California. Growth rings were narrower at breast height, latewood percentage tended to be greater, and tracheids were shorter in trees from higher elevation populations. Proportion of family variance components was greater than population for specific gravity and spiral grain angle. The characteristics that showed greatest population components of variation would be largely determined by durations and rates of shoot and radial growth. Presumably, length of the growing season would exert stronger selection pressure on these variables than on other characteristics of wood structure.