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Abstract

Eucalyptus globulus and E. nitens are among the most important plantation
eucalypts in temperate regions of the world. Although pulpwood production is the
principal focus of most forest growers, there is increasing interest in producing
sawn-timber from E. globulus and E. nitens plantations. This thesis investigated
breeding as a means of improving the solidwood characteristics of E. globulus and
E. nitens.
Data relating to genetic variation in E. nitens was collated from the literature.
However, only a small number of independent parameter estimates were available
for solidwood traits. This was similarly the case in E. globulus.
In E. globulus, the lower stem, which represents a high proportion of total stem
volume, was found to have the least favourable wood properties for kraft pulpwood
and most solidwood applications. Subrace by height category interactions in bark
thickness, basic density, decay and gross shrinkage indicated that differences
among subraces were dependent on height in these traits.
The utility of measuring shrinkage in small wood samples (e.g.12-mm cores) as a
cheap and non-destructive means of selecting against drying defects in sawn
products was investigated. A number of methods of assessing shrinkage in
samples were examined. Volume- and calliper-assessment of gross shrinkage were
deemed the most promising assessment techniques based on genetic and practical
considerations.
A strong genetic correlation between collapse and gross shrinkage in E. nitens wood
samples indicated that most genetic variation in gross shrinkage was explained by
collapse rather than normal shrinkage even when cores were dried at low
temperature. In E. globulus, strong genetic correlations in gross shrinkage between
drying treatments indicated that genotype by drying treatment interaction was of
limited consequence over a wide range of drying conditions.
Relationships between pulpwood selection traits and sample shrinkage traits were
investigated. Genetic correlations between basic density and gross shrinkage were
generally negative (i.e. favourable) in both species. In contrast, the strength and
direction of genetic correlations between growth and gross shrinkage varied widely between and within studies. In E. nitens, the genetic correlation between predicted
cellulose content and gross shrinkage was found to be positive (i.e. adverse) but not
significantly different to zero.
Although significant genetic variation was detected in shrinkage traits, the efficacy of
reducing drying-degrade in sawn boards by selecting trees according to sample
shrinkage remains unclear. A small-scale E. globulus sawmilling study identified
significant genetic variation in some board drying defects but did not find strong
correlations between sample gross shrinkage and these defects. Furthermore, a
very low intersite genetic correlation in sample gross shrinkage was observed in an
E. nitens study.

Item Type:	Thesis - PhD
Authors/Creators:	Hamilton, MG
Copyright Information:	Copyright 2007 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Copyright © the Author. Published material from within this thesis has been removed with hypertext links to the full referenced citation.
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