Over the last decade, the New Zealand Drylands Forest Initiative (NZDFI)
has obtained the largest collection of seed in the world for a number of
naturally durable eucalypt species, including E. bosistoana , with
the aim of establishing a fast-growing, naturally durable, super-stiff,
sustainable plantation timber resource in New Zealand. The basis is a
breeding programme which gives wood properties the same priority as
growth, form and tree health. This novel approach to tree improvement
also includes very early screening (age 1-2) to ensure a timely
deployment of improved germplasm \cite{Altaner2015}. With the “Splitting”
test, screening of the entire genetic stock is now a practical solution
to remove growth-strain induced wood defects. A 10,000 tree trial
consisting of ~200 families each with 50 half-sibling
replicates of E. bosistoana has been established. The trial will
be harvested at an age between 18 and 24 months (late 2016 - 2017) and
evaluated for growth-strain, as well as improved for early form, growth,
stiffness, volumetric shrinkage and basic density. As the tests are
destructive the superior individuals need to be rescued by coppicing.
Propagation of coppice cuttings is also providing a fast route to deploy
improved material to the forestry sector. Additionally, a number of
long-term field trials have been established (as early as 2009)
throughout New Zealand to provide longer term studies of wood properties
in particular heartwood formation.
Due to the nature of the “Splitting” test, strains which result in the
closure of the specimen cannot be measured, and as a result are recorded
as zero. Figure \ref{div-764179} shows a number of individuals exhibited closing,
particularly when grown from seed, indicating an atypical stress pattern
in the stem \cite{Meinzer2011} with greater contraction at the pith than the
periphery. The inverted stress-profile may be a result of tension wood
being formed by the trees at young age (i.e. at the centre of the stem)
to straighten the stem followed by normal wood with lower axial tensile
growth-stresses at the periphery. Trees can form reaction wood in
response to wind loading \cite{Coutts1995}. A closing sample may indicate
increased sensitivity to wind loading and the development of reaction
wood at a young age in that genotype. In order to better understand the
mechanisms for this unusual behaviour, a new trial has been established
in which initial bending will be induced in the stems at a young age
followed by straightening.