A study of spatio-temporal variation of Eucalyptus nitens fibre morphology – a multivariate clustering and nonlinear time series approach
by
Irene Hudson
Department of Mathematics and Statistics, University of Canterbury
Coauthors: Michelle Dalrymple

Eucalyptus nitens (shining gum) and eucalyptus globulus (blue gum) are important sources of fibre for the Australian and NZ paper industry. Eucalypt hardwood cells are the product of physiological and genetic processes starting with the differentiation of the cambium. Factors such as age, growth rate and stresses, site and genotype and size of cambial initials determine wood microstructure and the inherent variability in wood properties. The majority of studies of wood fibre variation in the literature have focussed on two components of within-tree variation; (i) longitudinal (with height) variation and (ii) radial variation; from pith to bark. Formal testing of a possible interaction between longitudinal and radial variation in eucalypts and accommodating for the significant within ring variation (ELW), from early seasonal (earlywood (EW)) to late season (latewood (LW)) growth, are important precursors to testing for possibly new oblique and/or cylindrical axes of variation within trees.

It is shown, using both multivariate clustering and a non-linear multivariate time series (NLMVTS) approach that fibre variation in E. nitens can be referenced to a axes governed by - ring structure, season (ELW), chronological age (YR), height (HT), ring-specific attained height (AH) and cambial age (CA) (CA is related to the time the first vascular cambial cell formed at a given height and ring.).

We show that the change in fibre dimensions radially differs significantly between sampling heights in E. nitens and that longitudinal variation differs according to (a) closeness to pith or cambium or (b) within-ring position according to closeness to EW or LW boundaries in E. nitens. These results indicate a possibly pseudo cylindrical pattern of whole tree variation in E. nitens. This is in contrast to the significant oblique whole tree variation evidenced in E. globulus (Hudson IL, Dalrymple M, Wilson LF (1999); Biometrics 99 Hobart).

Using NLMVTS methods and clustering algorithms we can also show that the ELW variation differs across rings and sampling heights in E. nitens and seems to be governed by CA. At all sampling heights and rings in E. nitens, EW to LW segments exhibit specific fibres which can be identified as a repeating permutation of a particular 7 cluster sequence; similar to a repeating DNA sequence. This paper highlights the importance of understanding the role of cambial physiology and seasonality on whole tree fibre variation. Genetic manipulation, particularly of cambial activity, may provide a means of producing fibres with specific dimensions for given end-uses.

Date received: August 30, 2001