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\begin{document}

\title{A critical review of very early selection protocols in tree breeding for
timber}



\author[1]{Nicholas Davies}%
\affil[1]{University of Canterbury}%


\vspace{-1em}



  
  \date{May 08, 2024}


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\section*{Introduction}

{\label{262471}}

Breeding of crops to maximize particular attributes is~ something
humanity had done for generations. Examples such as corn or tomatoes are
now very different from their wild ancestors, however, with forest trees
used for wood products much smaller changes have been made. One of the
reasons for the slower advance is the comparatively long breeding cycle
time. In order to make significant advances in the manipulation of
properties of forest trees to maximize their benefit for use in human
products, breeding cycle time needs to be reduced.~~

\par\null

Initially there are two problems which need to be solved in order for to
reduce the breeding cycle. One, propagation before individuals reach an
age of reproduction, and two, reliable selection of individuals for
desired properties very early in their lifespan. The propagation problem
is not of concern here and can be solved through various
micro-propagation techniques, for background information
see~\cite{Baker_1992,Watt_2003}.~ The problem of predicting future attributes
from very young trees has seen some attention over the last decade, for
convenience this will be referred to as the early selection problem. In
essence trees change a number of properties during their life time as
their interaction with the environment evolves. Particular properties
which exist at young ages will not necessarily exist at older ages and
visa versa, because wood is preserved during growth those properties
will exist in the wood laid down at that point in the trees' life, for
example in the pith. Wood properties near the pith may degrade or be
damaged later in life through various processes.~ The relationship
between one or more wood properties at different positions in the stem
may influence some macroscopic property of interest to breeders, for
example deformation during sawing.

\par\null

A major problem with very early selection was discussed in detail
by~\cite{Apiolaza2009}, essentially he argued that even with a high year
to year autoregressive correlation for a trait, a 15 year lag between
measurement and harvest makes the association between selection
criterion and objective trait value virtually non-existent. A
consequence is very early selection can not be reliably used for
maximisation/minimisation selections.~\citet{Apiolaza2009} made it clear
at the time very early selection~ is usable only when the aim is to
reach a non-reversible threshold, ie a screening problem. The example
given was stiffness where he argued because MFA is known to only reduce
with age and density does not decrease with age (the two traits which
govern stiffness), and grading of stiffness is a threshold problem it is
advantageous to get wood to the threshold as early in life as possible,
but only because once the threshold is met further gains do not increase
value, and there is strong physiological evidence to show that the trait
value will not dip back below the threshold later in growth. To further
the argument ~\citet{Myszewski2004} found non-significant genetic
correlations between rings 4-5 and 19-20 for MFA (and therefore likely
stiffness and growth-strain as MFA is thought to be the a significant
factor in both cases). As an example; two trees reach a threshold
stiffness at age 5 of 2 GPa, and one has a stiffness of 3 GPa at age 10
and the other has a stiffness of 9 GPa at age 10.~ Both trees met the
threshold stiffness at the same time so are worth the same amount, but
the correlation between stiffness at age 5 and age 10 is non-existent.~

Currently no trials have been set up specifically to investigate GxE
with very early selection methods. As a result little is known about how
early selection methods will perform outside of the environment in which
they were selected even if only considering properties at the age of
selection. GxE is an important part of a tree breeding cycle, as
properties differ from one environment to the next, and the level of
genetic control independent of the environment needs to be quantified in
order to create a good selection. Which genetics perform well in which
environmental conditions needs to be quantified and used during~decision
making processes to ensure the appropriate genetics are deployed at each
unique site~~\cite{White2007}. In the future investigating how
reliably GxE iterations can be predicted at young ages should be a high
research priority. Currently no known experiments have been setup for
this purposes and the available data does not have significant genetic
overlap to obtain meaningful results for any traits. Even at older ages,
large numbers of trials are needed to accurately separate genetic and
environmental effects.~\citet{Dieters1995} investigated 171 tests of
slash pine consisting of over 2100 full sibling families from 170000
individuals. Heritabilities taken from one or a small number of sites
can produce almost any heritability between 0 and 0.5, unbiased
heritabilities (heritabilities taking into account site effects) ranged
from 0.072 to 0.12 depending on age, showing the importance of having
large GxE trails and ensuring appropriate age
distributions~\cite{Dieters1995}. Without significant GxE investigation,
genetic parameters can be extremely misleading. Further, along with
expressing consern about differing genes being responcable for growth at
different ages, \citet{white1992} suggested large site index
differences between progeny test sites and commercial production land
will decrease the reliability of progeny test data in predicting
breeding values.

Caution needs to be taken when breeding for traits in trees in general
and even more so with very early selection. Breeding trees to obtain
particular traits at very young ages may result in unforeseen problems
associated with the selection later in life. For example, breeding stiff
trees at very young ages may result in increased mortality from wind
throw as the ability to bend in a young stem has been suggested to be a
trait which has evolved due to the low second moment of area in the stem
\cite{Davies2014}. By reducing the ability for a small stem to bend, it
will be more likely break or topple in strong wind events or when
animals walk over or push it. Another example may be the development of
above ground growth at the expense of root system development resulting
in increased uprooting during severe wind events. Unfortunately breeding
trial failures such as these are rarely reported in literature and
therefore quantifying them is difficult. There is further potential for
problems such as these to develop with very early selection protocols,
but without running both very early selection and full length breeding
trials in parallel over different environments with the same genetics it
will be very difficult to identify negative traits developing as a
result of very early selection.~

\par\null

\section*{Discussion}

{\label{721644}}\par\null

There are a number of attributes tree breeders are now wanting to select
for; growth, health, form, durability, density, stiffness, growth-strain
and volumetric shrinkage. Broadly these can be separated into two
categories, maximization/minimization selection and threshold selection.
For example, usually growth is maximized, while if form reaches a
specific criteria it is considered good enough. This is an important
distinction when coupled with tree physiology as trees present general
patterns with some wood properties (such as MFA) which rarely reverse
with age~\cite{function2011}. As a result, when a threshold selection can
be coupled with a trait which is governed by physiological
characteristics which are known to develop in a particular way and if an
appropriate test can be developed for that trait they could be selected
at a young age. An example is stiffness within~\emph{Pinus radiata}
where MFA is known to decrease and density increase with
age~\cite{Xu_2004} , resulting in stiffness increasing with
age~\cite{Sharma_2015}. Because a premium is paid once a predefined
stiffness is reached it is a threshold problem where once the threshold
is reached all later growth can (reasonably) be assumed to be over the
threshold . An example where this type of selection does not work is
growth, as the individuals which are desired grow to the largest size
possible in the shortest about of time, i.e. a maximization problem.
As~\citet{Apiolaza2009} alluded to, in order for very early selection to
be profitable a switch in thinking is needed to the screening/selection
to be only for wood produced early in the trees lifespan (corewood),
extrapolating that information to older (outerwood) wood properties is
problematic and can only be done when there is sound physiological
reason, otherwise the autoregressive nature of wood properties through
time results in no gains being made.~

\par\null

Various wood property traits will be addressed individually and their
appropriateness for very early selection (arbitrarily defined here as
selection at less than 20\% of their commercial lifespan or a grater
than 10 year lag between selection age and commercial harvest age)
discussed with reference to literature, unpublished pilot trials and
thought experiments. Where possible root causes for (un)suitability will
be linked back to~ physiological understanding, or lack there of and
suggestions will be made as to future research directions in order to
increase the effectiveness of the tools used.

\par\null

\subsection*{Growth}

{\label{713235}}\par\null

Growth, height, diameter and volume are discussed together as are very
intertwined in todays breeding trials with diameter often used to
predict height and volumes estimated from the two. These all fall into a
maximization class breeding problem; volume is maximized over a
predefined time frame.~Because growth can be measured non-destructively
research has been conducted investigating the ability to predict a trees
future growth performance at differing ages, and~ verified on the same
tree later in time. ~\citet{Dieters1995} investigated genetic
correlations between volume measurements at differing ages and found the
correlations to vary between 0.56 and 0.97 for lag times of between 3
and 9 years, with young trees producing poorer correlations than older
trees even when the lag time was the same, others have found similar
results \cite{Mihai_2016,whiteman1997,Stackpole_2009,Osorio_2003}.

\par\null

There is an argument for very early selection of growth and mortality
which states something akin to ``nurseries pick the top performing
individuals at the age of a few weeks, therefore it stands to reason
that the same could be applied at any age'' However nurseries are
picking individuals which are the most likely to survive the process of
transplanting from the nursery bed to the forest, which requires a much
shorter time frame prediction (a few weeks, not decades) and is a
threshold problem, either the trees survive transplant or die.
Physiologically larger individuals likely have more nutrient storage,
more developed root systems, and larger canopies, giving them a
competitive advantage over smaller individuals in a transplanted
situation where they must re-establish and compete with other plants for
resources. Nursery selection in this way makes no assumptions regarding
how well the tree will perform later inline, it merely takes the
individuals which at the time of picking has the physical
characteristics which will help them service transplanting.

\par\null

Silvercultural practices can have large influences on growth and
different genetics can respond in differently to silvicutural practices
\cite{ashton1997}. Very early selection occurs before trees are large
enough for pruning or thinning and are treated in very different ways to
a typical commercial stands, for example they may be planted at very
high stockings to save money and have irrigation on highly fertile soil
to lower mortality.~ Any genetics which thrive under these ideal
conditions will be selected above others which may be better suited to
the real world. For example, an individual which is slower growing but
has high drought tolerance is not selected in an irrigated trial, but
the selected fast growing individual then dies when is planted out in a
dry area.~

\par\null

\subsection*{Health}

{\label{560559}}\par\null

Early selection for health appears feasible as a threshold criteria,
only select trees which are healthy at the end of the breeding cycle.
Once a tree has become sick (or died) it will lag behind other
individuals in its stand giving suboptimal growth. If trees die or are
excluded from very early selections due to poor health they are not
included in the next breeding cycle (even if not directly selecting for
health). Any undesirable heath problem which occurs during the very
early breeding cycle and from which resistance is heritable can be
selected against. However health problems which are associated with
older ages can not be predicted using this crude early selection method
of ``if its not healthy dont select it''. Establishment health is a good
candidate for very early selection, although it should be kept in mind
that differing environments will cause different health challenges.
Health is used as a broad term, but the genetics required to withstand
drought are different to those required to withstand frost, or beetle
attack. Identifying genetics with resistance to particular environmental
pressures at a young age should improve planting out success of future
trials if genetics are chosen appropriately for the environment,
reinforcing why GxE trials are of the utmost importance.~

\par\null

\subsection*{Form}

{\label{789961}}\par\null

Form is characterized by the repetition of particular stem and branching
characteristics. Trees used in very early selection typically have not
been growing for long enough to show any repetition of traits such as a
tendency to double leader, have large branches, or small internodes.
Because of the lack of repetition, form in the traditional sense is hard
to utilise within very early selection programs. When domesticating a
wild species extremely poor individuals may still be recognizable at
young ages, although the concept of form selection needs to be slightly
redefined for very early selection programs. If an individual is ``bush
like'' as in ``at a small size it does not prioritize vertical growth''
(assuming no mechanical damage has occurred),~ it seams reasonable to
remove the individual from the breeding population because in this state
it will become sub-dominant and struggle to regain the growth required
to produce a straight stem of suitable size under a typical single age
single species commercial stand management strategy, and be removed
during thinning ( if thinning was part of the stand management
strategy).~ It seams unlikely that any domesticated species (even if
only one breeding cycle has been completed) would still have genetics
which produced individuals with form this poor. The strategy also
provides no guaranty that remaining trees will possess satisfactory form
characteristics at older ages. Very early form selection at best will
remove the genetic anomalies such as highly inbred individuals of
undomesticated species which are prone to ``bush like'' growth at young
ages as the information required to asses an individual for form in the
traditional sense is simply not available until significant repetition
of branching and stem traits is measurable at an older age.~

\par\null

\subsection*{Density}

{\label{185693}}\par\null

Density is probably the most used wood property in breeding, although
possibly due to the low measurement cost and high speed compared to
other wood properties~\cite{apiolaza2008}. When maxamising material is
the main concern, for example breeding for carbon sequestration, pulp or
biofuels, maximising density makes sense, and while no early selection
programs are known to exist for this purpose, if the trait can be
expressed as a threshold of density the potential exists for very early
selection to be valuable as density does not generally reduce with
cambial age~\cite{function2011}. Initially density gained a lot of
attention as it was easy to measure and originally thought to correlate
well with wood properties such as stiffness. In young trees, both
Eucalypt (Chapters 3 and 4) and Pine~\cite{Sharma2015} the correlation
between stiffness and density is low. It could potentially be the case
that when creating engineered wood products, selecting for a specific
density may be of importance~\cite{marra1992} e.g. gluing may work
best at a given density value. Density doesn't decrease with cambial
age~\cite{function2011} and if keeping density above a lower threshold
is desired it is a good candidate for very early selection methods.
Given the TRP of density shows an increase (or at least no decrease)
with age, very early selection is unlikely to be reliable even if low
density individuals are selected at a young age. There is no evidence
that the selected trees will not go though a more rapid density change
than the individuals which were not selected after the very early
selection time frame. As a result, the selection could be counter
productive and provide a genetic base of inferior trees.~

\par\null

\subsection*{Stiffness}

{\label{823752}}\par\null

Stiffness is generally a threshold problem, timber is graded using
threshold stiffness values to define a particular price bracket. As a
result, nothing is gained from maximizing stiffness above the desired
threshold. Because stiffness is governed by acoustic velocity and
density, both of which under normal circumstances follow a fairly
universal pattern of decreasing MFA and increasing density with distance
from the pith \cite{function2011}, if a desired stiffness is reached
early in life it is reasonably assumed the stiffness of wood laid down
later will not dip bellow the threshold. The combination of threshold
selection and well established age-related physiological patterns make
stiffness a good candidate for very early selection. Stiffness selection
can also be formulated as a minimization problem; How early in life can
a tree reach the desired stiffness. Due to testing constraints,~
measuring breeding populations in this manner is not feasible, however,
harvesting at predetermined (early) age and selecting individuals which
reach the threshold will likely result in a population reaching
threshold stiffness earlier and hence provide stems with more wood
usable in the higher value stiffness categories (for the given site,
although the argument can be readily extended to GxE trials). A
potential problem with very early selection of stiffness is by
increasing stiffness of young (small) stems there will be a reduction in
flexibility to resist toppling forces from animals and wind events. One
of the most promising arguments for the evolution of the typical radial
pattern of MFA and density is that trees experience differing mechanical
loading depending on their size~\cite{Mattheck_1997}, there is a
biological advantage in having low stiffness when a stem has a low
second moment of area, allowing for the stem to bend rather than break
or topple when external forces are applied. As the second moment of area
increases with diameter, the geometry of the stem plays a proportionally
larger role than the stiffness of the stem than the material properties
do. Once a stem reaches a significant diameter bending ability becomes
compromised and hence the best defense strategy is to stand solid,
making stiffer material more desirable. By breeding to have stiff
material in small stems there may be an inadvertent increase in toppling
or breakage at young ages, possibly outside of the age range of very
early selection trials, or the trial may by chance not experience the
required weather event due to its short cycle time.~

\par\null

\subsection*{Extractive Content}

{\label{441872}}\par\null

Extractive content could use similar selection type to stiffness, once
trees start producing heartwood they (with the exception of some rear
cases such as striping) don't stop. Therefore selection of individuals
at an early age which have started producing extractives (assuming that
the production of extractives is heritable) could lower the age at which
the population starts producing heartwood. Further evidence exists that
the worst heartwood exists in the pith and improves in resistance to
decay with radius~\cite{Kokutse_2006,Bhat_2003} so it may be possible to set a
threshold at a young age for the timbers durability as well. There are
two conceivable reasons to select for the presents of particular
extractives - one, the presents of extractives is required for natural
durability, and two, the colour of the wood may fetch a premium. If
extractives are present at a young age it does not guaranty that the
individual will have superior durability, but the presence of
extractives is required for durability and therefore assuming extractive
content and durability are heritable, very early selection may have
potential as a starting point for selection of this trait. However
little is known about the relationship between durability and extractive
content, which needs further investigation before its suitability for
very early selection can be assessed. As heartwood tends to develop
later in a trees life (compared to when very early selection takes
place) it is unlikely any trees will be producing heartwood at the time
of selection. Any proxy based selections should be treated with due
caution, and a good understanding of the underlying physiologically
between the proxy trait and later development of heartwood would be
needed, currently no known research has identified or suggested a
suitable proxy trait, backed by sound physiological theory.~~

\par\null

\subsection*{Growth Strain}

{\label{927797}}\par\null

There are a number of issues associated with trying to select for growth
strain at any age. First growth strain, in the sense of a breeding trait
needs to be defined. The breeders' desire with this trait is to capture
genetics which produce little or no movement during sawing. Minimization
of movement during sawing (or reducing movement below a threshold),
which breeders have been calling growth strain is not necessarily the
same as what physiologists call growth strain (derived from growth
stress). Growth strain in the strict sense is a contraction which
happens in the secondary cell wall during formation (see Chapter 1),
when combined with numerous other geometric and material properties it
produces movement at the macroscopic scale when boundary conditions are
relaxed (for example during sawing, or a typical strain gauge test),
giving what breeders have been referring to as growth strain.~ If
selection was to take place only considering cellular level growth
strain, it is related to MFA, however MFA and growth strain are
correlated, making an inverse threshold problem, i.e. MFA must not go
below a value associated with undesirable growth strain. In order to
accomplish this the whole lifespan is needed as the MFA TRP decreases
with time~\cite{function2011}, and consequently growth strain
increases.~Growth strain is expected to increase to some unknown maximum
occurring at some unknown time, which cant be known to be reached until
the desired age of felling.~\citet{Biechele_2009} found experimental
evidence of an increase in surface strain with age and concluded that a
multivariate approach is needed in trees of saw log dimensions as all~
growth parameters (crown width, crown area, crown eccentricity, crown
length, tree height, DBH and slenderness in their case) have low
correlations with growth strain.~\citet{Biechele2009} suggests
interactions among parameters may also be useful but warns due to the
large number of interactions growth strain its self may not be~ a useful
breeding property.~

\par\null

Timber movement during cutting is~ influenced by a number of material
and geometric properties such as MFA, reaction wood production, grain
angle, crown shape and stem lean. Crown formation, soil conditions,
prevailing and extreme wind events could all cause stem lean or an
asymmetric crown which would result in an increase in growth strain
within certain areas of the stem along with asymmetric stem formations,
and as a result could cause more, less predictable deformation during
sawing. More complicated as movement in mill (or during testing) is
dependent on multiple inner wood properties such as spiral grain and
crown habit (form) changes in time. It may be that genetic selection for
low movement timber at milling is not possible due to the large number
of genes responsible for so many properties which effect local GS
production, which in turn creates a complicated three dimensional strain
field within the stem. There are a lot of properties which would need to
be simultaneously either maximised or minimised within an individual,
and their correlations may not be favourable. For example, low base
growth strain, low tendency to produce reaction wood, poor performance
of reaction wood produced, symmetric crown and stem properties. Further
complications arise as the traits which influence the magnitude of
strain at a given point of development change with time, as a result
different traits would need to be maximised/minimised at different
stages of development in order to manipulate the production of the three
dimensional strain field to produce the least amount of movement at the
time of milling. It seams very unlikely this is achievable though
breeding even over multiple sites and using full length breeding cycles
due to the large numbers of traits which would need to be manipulated,
some of which may not have a significant level of heritability, may have
strong environmental interactions or are negatively correlated with
other required traits. The most promising rebuttal to this argument is
the mechanisum of growth strain production is under high genetic control
and for some reason does not just lay down more reaction wood to get a
given force, i.e. the amount of reaction wood will be consistent for a
given influence, however the stress that reaction wood is capable of
could be under simple genetic control.

\par\null

An argument could be made that because growth strain is so heavily
effected by verious micro-environmental aspects site level
characteristics such as rain fall, aspect, soil type etc. will have less
of an effect than on other properties, although no evidence exists for
this. If it is the case that so many different properties influence the
production of growth strain the variation between individuals within a
site compared to the variation between sites would be much smaller than
other traits which are controlled by less complex generation mechanisms.
Growth can be significantly hindered by a lack of water, and that will
effect all (say cloned) individuals more-or-less equally on a given
uniform site. However with growth-strain, a broken branch, being pushed
over by an animal, a wind tunnel effect etc. could all alter the growth
strain from tree to tree even though the site level environment is
essentially uniform and the genetics are identical. Whether this
argument is valid should be investigated in the future as it may have a
profound effect on the way genetic-environment interactions are
considered within breeding programs as technology advances and
individual tree monitoring becomes more realistic. Further, if it is the
case silvicultural techniques will likely be better suited to growth
strain manipulation than breeding.~

\par\null

Currently there is a significant knowledge gap regarding what material
and geometric properties result in timber movement during (green)
sawing. Further there is a lack of understanding of the strain field
within a given stem, and how the field relates to the deformation of
timber during milling. Before very early assessment of tree level growth
strain can be considered for incorporation into a breeding program, an
understanding of what causes timber deformation during green sawing is
needed. Once an understanding of how the field relates to deformation,
work is needed to investigate the influences which create the strain
field, only then can those properties be investigated and tools
developed to determine if selection for low growth strain as a means of
reducing sawing deformation is feasible.~

\par\null

If we assume low age-age correlation of surface growth strain (or even a
moderate one, which there is currently little evidence either way), it
could be argued that selection for high surface growth strain of young
trees which slowly reduce with growth may be the optimal profile. High
surface strain in small stems (the wood on the surface is under tension)
provides a flatter profile over the majority of the stem when the tree
is much larger, so the gradient from one side to the other of a board is
lower potentially resulting in less deformation. While there is no
evidence that strain at a young age is a poor predictor of strain at an
old age, the reverse does not have any evidence either (but it is much
more common in other traits for young cambium properties to be poor
predictors of older traits~\cite{Apiolaza2009}), it is worth considering
that a potential result of selecting for low surface strain at a young
age may have the unintended consequence of increase saw board
deformation at commercial harvest age. This argument reaffirms the need
to have significant physiological understanding of how a trait is
produced before proxy tests (whether they are proxies in time or
property or both) are used for selection.

\par\null

\section*{Conclusions}

{\label{116146}}\par\null

\citet{genetics2007} presented a list of requirements for a successful
tree breeding program.

1) clear program and product objectives

2) sound knowledge of biology, silviculture and genetics

3) sound breeding strategie, well trained personal supported by a stable
budget

4) efficient mass propagation nursery and plantation management~ systems
to optimize yield and product quality

5) maintenance of broad genetic base

6) supportive research program

\par\null

These points become even more crucial when considering very early
selection as additional errors are added in order to reduce breeding
cycle time. Due to the unknown relationships between various properties
at different ages and how they will effect each other at commercial
rotation age, having clearly defined program and product objectives is
strongly linked to having sound understanding of the biology,
silviculture and genetics of the species, both of which can only be
achieved with a supportive research program which focuses on fundamental
understanding of how the trees grow and why. Without this knowledge it
will be nearly imposable to develop reliable testing procedures for very
early selection.~~

\par\null

There are two ways to develop very early selection methods once a
suitable level of understanding of tree development is achieved. One is
to have sufficient fundamental understanding that given properties at
one age guaranty given properties at another (stiffness from MFA and
density for example). The second option is a statistical approach,
either using periodic non-destructive testing on the same individuals to
obtain age-age correlations (DHB or height through time for example) or
specifically designing trials to test how well destructive tests at one
age predict properties at another ideally using clones. For this to be
successful environmental factors need to be considered, one option is to
clone trees at full rotation age from multiple (significantly different)
sites which share genetics and test the clones under the intended very
early selection procedures, typically high stocking within a nursery
site. If a sufficient number of individuals, families and environments
are represented a relationship between how well the given very early
selection procedure (for that trial) can estimate outcomes on the
different sites at different ages can be obtained and hence the site and
procedures could be used to accelerate breeding cycles provided none of
the above change significantly and the age-age correlations for the
traits are sufficiently high.~

\par\null

The above discussion leads to the conclusion that for a trait to be a
viable candidate for very early selection (in addition to significant
levels of heritability, genetic variation, environmental variability
etc. which are required for success for all breeding programs) at least
one of the following three is required:

1) Extremely high age-age correlations. No known evidence exists stating
that any of the properties discussed here poses significantly high
age-age correlations. Truthing at full rotation age would be required to
estimate age-age correlations over multiple environments.

2) A non-reversible threshold problem governed by physiology eg
stiffness and possibly heartwood quality.~

3) A trait which is defined within the very early selection breeding
cycle life span, for example planting survival at one year.

If the following can be met, full rotation age trials are still
continually required to ensure inadvertent traits are not being selected
for.~

\par\null

Very early selection may provide some substantial gains in breeding
efficiency for a limited number of wood properties, however development
of the procedures needs to come from thorough understanding of the
biology, physics and genetics of both the trait and the testing
procedures, further it needs to be truthed with full rotation age trials
from multiple environments. Full rotation age individuals need to be
tested and the population characterised across multiple significantly
different sites with sheared genetics first, and then a very early
selection test could be developed and the results compared across sites
and properties of the full rotation age trees. While commercially it is
tempting reverse this procedure and complete very early selection first,
there is no evidence of any positive or negative gain being made and
will likely waste substantial amounts of time and money.~

\par\null

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