Relationships between the intra-ring wood density assessed by X-ray densitometry and optical anatomical measurements in conifers. Consequences for the cell wall apparent density determination

Overview & Synopsis

The objective of this work is to compare anatomical measurements to wood density variations within annual rings of three major softwood species, Norway spruce, Scots Pine and Silver Fir. The six selected annual rings were sampled within a database of thousand microdensitometric profiles measured on wood samples collected in Finland and France. Each of the six studied annual rings represents one average profile of wood density for a given age class and age ring width. The dimensions of the tracheids are performed in the radial-tangential plane by using two different planimetric methods. The wood density profile within each ring is calculated simply by the mean of the tracheid dimensions and by using a constant value for the cell wall density. We have verified that the knowledge of the (i) tracheid geometry and (ii) the usually admitted value of the cell wall density allows us to calculate intra ring wood density profiles which are similar to the X-rays wood density profiles in terms of variations but very different in average. Thus it appears necessary to calibrate by using an apparent cell wall density varying inside the rings and being far weaker than the effective cell wall density of 1460 kg/m³ as it is usually admitted in the literature.