Modelling radial and longitudinal microfibril angle variation in Scots pine

1 Context Microfibril angle (MFA) is one of the key determinants
of solid timber performance due to its strong influence
on the stiffness, strength, shrinkage properties and
dimensional stability of wood.
2 Aims The aim of this study was to develop a model for
predicting MFA variation in plantation-grown Scots pine
(Pinus sylvestris L). A specific objective was to quantify
the additional influence of growth rate on the radial variation
in MFA.
3 Methods Twenty-three trees were sampled from four mature
Scots pine stands in Scotland, UK. Pith-to-bark MFA
profiles were obtained on 69 radial samples using scanning
X-ray diffractometry. A nonlinear mixed-effects model
based on a modified Michaelis–Menten equation was developed
using cambial age and annual ring width as explanatory
variables.
4 Results The largest source of variation in MFA (>90 %)
was within trees, while between-tree variation represented
just 7 % of the total. Microfibril angle decreased rapidly
near the pith before reaching stable values in later annual
rings. The effect of ring width on MFAwas greater at higher
cambial ages.
5 Conclusion A large proportion of the variation in MFA
was explained by the fixed effects of cambial age and annual
ring width. The final model is intended for integration into
growth, yield and wood quality simulation systems.