Influence of cambial age and growth conditions on microfibril angle in young Norway spruce (Picea abies [L.] Karst.)

Microfibril angle (MfA) of the tracheid cell wall of conifers influences the performance and properties of forest products. For instance a high MfA has been found detrimental for solid wood properties. Although it is assumed that there is a correlation between MfA and the growth conditions a tree experiences, there are few studies on how growth conditions influence MfA. In this study mean MfA of the cell walls was determined for 646 early wood samples, from pith and outwards, of Picea abies trees using automated double gaussian curve fitting of the 002 area generated by X-Ray diffraction and recorded using a area detector. The determinations of mean MfA were based on appr. 500-2000 tracheids per wood sample. It was indicated that a determination of mean MfA would require less than 3 minutes, if the curve fitting program is included already at the time of data acquisition. In an attempt to model the dependency of MfA on factors related to wood formation, the age effect was found most descriptive and a simple model based on 1/cambial age gave an r(2) = 0.69. Only a slightly higher correlation (r(2) = 0.73) was reached when additional variables significant at p less than or equal to 0.001 were used, although they, together with the age effect, supported the assumption that growth conditions affect MfA. The study suggests that to concentrate and minimize the volume of wood with high MfA, in an individual tree, juvenile growth suppression in combination with an extended rotation period should be used.