Variation of microfibril angle, density and fibre orientation in twenty-nine Eucalyptus nitens trees

SilviScan-2 was used to estimate and map microfibril angle (MFA) and densit y in twenty-nine 15-year-old Eucalyptus nitens trees;:Over 4000 MFA measure ments were made at about 100/hour. Each measurement represented a weighted average for about 50000 fibres, After an initial decrease near ground level , density increased with height in the stem. MFA decreased with height in t he stem, reached a minimum around 30 to 50% of tree height, then increased towards the top. In the radial direction, density first decreased for a few years, then increased towards the bark. MFA was in the range 20 to 30 degr ees near the pith at all heights and generally decreased towards the bark o ver most of the height of the stem. The lowest MFA values (approx. 10 degre es) were found close to the bark at 30 to 50% of stem height. Both density and MFA varied more rapidly near ground level, increasing the uncertainty o f correlations between breast-height properties and whole tree properties. On some samples, high-resolution (0.2 mm) MFA scans were performed to confi rm an earlier finding that MFA is strongly inversely correlated with densit y over a few growth rings but not over larger distances. X-ray diffraction was also used for estimating the orientation of the fibres within the sampl es. The radial variation in fibre orientation generally decreased with dist ance from the ground. Breast-height sample properties were moderate to good predictors of whole tree properties. Better correlations were obtained usi ng samples from 5.5 m. Whole tree average density and MFA were found to be uncorrelated, indicating that tree improvement strategies could be designed to simultaneously optimise these properties.