Spatial Distribution Within Trees

Traditionally, around the world the terms juvenile wood and mature wood have been taken to relate to cambial age, i.e. juvenile wood is the wood surrounding the pith that is formed by the young (juvenile) eambium. Confusingly, in some Southern Hemisphere countries the terms corewood and outerwood refer to the same radial gradient in wood quality. To avoid - or add to ( ) - any potential confusion, this text follows the new convention proposed by Burdon ei al. (2004) that has yet to achieve broad consensus. 

Wood quality varies within trees both in the radial and axial direetions. Burdon et al. (2004) propose a two-dimensional framework with the radial variations deseribed in terms of corewood and outerwood and the axial variations deseribed in terms of juvenile and mature wood. Arbitrarily, corewood has been described as a eylindrieal zone enclosing the first few growth rings around the pith. Typically, for fast grown pines this zone around the pith is considered to be of poor quality, having a number of undesirable features (Zobel, 1975)  

While the juvenile zone only extends upwards for a few metres, this zone is encompassed by the butt log that, by tradition, is valued because of its size. As with the corewood-outerwood boundary, there are tree-to-tree and species-to-species variations in the vertical extent of juvenile wood and in the rate of change in wood quality toward the tree top. Cuttings from older branches lack juvenile responses to silvicultural practices and the benefits of physiologically aged cuttings are improved form and stiffness, i.e. minimizing the juvenile core but at the cost of some loss of vigour. 

The exhaustion of natural forest resources is forcing industry to come to terms with the corewood of plantation timber. As its properties are better understood industry is finding appropriate end uses that reflect the intrinsic properties of the individual 

Indeed in some parts of the world plantation-grown trees harvested for commercial uses are composed entirely of juvenile wood, examples being 10-15 yr-old Paulowania and Populus sp. in parts of China (Bao et al., 2001). Fortunately the differences between corewood and outerwood, and between the juvenile wood and mature are not nearly as obvious in hardwoods (or maybe they are less well categorized). 

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Various plants such as moss, bryophytes, lichen, leaves, and tree bark have also been employed as bioindicators to monitor airbome PAHs pollution levels, assuming that then-spatial pollution distribution in the plants and the atmosphere will be closely related [117,122,123,363,364]. This aspect has already been revised in this chapter within the section... 

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