We propose a method to estimate fibre length distribution in conifers based on wood samples from
increment cores processed by automatic optical fibre-analysers. Automatic fibre-analysers are unable
to distinguish: a) fibres from other tissues, “fines”, and b) cut from uncut fibres. However, our
proposed method can handle these problems if the type of distributions that fibre lengths and fines
follow is known. In our study the length distributions of fines and fibres were assumed to follow
truncated normal distributions, characterised by means and standard deviations of the two distributions.
Parameter estimates were obtained by the maximum likelihood method. Wood samples
from two 22-year-old Scots pine trees at breast height were used to evaluate the performance of
the method. From stem discs at 1.5 m, adjacent samples of 5 mm increment cores and wood pieces
were taken. The cores were trimmed 1 mm at each side and samples were, after maceration,
analysed in a Kajaani FiberLab 3.0. The results showed that the method works well and gives a
possibility to distinguish fine and fibre length distribution.