Wood processors pay premiums for stable and stiff timber, while forest
growers often prefer to have fast growing trees as to shorten rotation
lengths increasing profitability. The preferences are not always
aligned, particularly within wood properties. Stiffness, used for
grading logs, is positively correlated with growth-strain with a
correlation of 0.61, an unfavourable correlation requiring a trade-off
between the two traits. While zero growth-strain is desirable to be
economically viable to process, some unknown maximum value below which
little economic loss is experienced exists. Stiffness is already used
for log grades, structural timber in New Zealand requires 8 GPa \cite{b2005}. To meet these stiffness grades at age two, some
compromise with the level of growth-strain in the stems is needed.
All stems measured within each family were averaged to give correlations
between properties at the family level (Table \ref{960788}). A very strong positive
relationship is evident between growth-strain and stiffness at the
family level. This means that reducing growth-strain will require
reducing wood stiffness at the population level. On the positive side,
some Eucalyptus species have such high wood stiffness that a
reduction would not have practical implications from a wood processing
viewpoint.