We have made some alterations to the original Chauhan & Entwistle
method to convert it from a research to an operational technique but the
effect of these changes should be negligible. The linear error
introduced by using large-end diameter rather than average diameter of
the stem will result in a slight reduction of all reported strains over
the original method. Leaving the small-end intact (that is, not cutting
it as in the original splitting test) does not release as much strain as
the original method, again lowering the growth-strain value over all
samples, however, given that a single measurement is now taken, rather
than two, measurement error is reduced. Further work is required to
determine the accuracy and precision of both tests and to separate
natural within-stem variability, from variability between stems.
Heritabilities presented here are for E. bosistana at age two, at
later ages these heritabities may change. From a breeding perspective,
these values are from a wild, unimproved population, and hence there is
considerably larger variability than in older breeding programs. Even if
heritability reduces with time, by removing the worst performing
individuals from the breeding population going forward, budgets can be
more efficiently spent only assessing the trees with a higher chance of
producing a premium quality product in longer term, substantially more
expensive breeding programs.
Genetic gain per unit of time for a breeding programme depends on four
elements: variability for the trait under selection, selection intensity
(proportion of individuals selected), accuracy of prediction
(proportional to heritability) and time required for turning a breeding
cycle. New phenotyping techniques, like rapid growth-strain testing,
increase selection intensity (as more trees are able to be assessed),
and reduce selection time (as trees can be less than two years old when
tested). As far as we are aware, variability for early wood properties
is not smaller than at typical selection age, and the degree of genetic
control is also similar \cite{Apiolaza2011}.