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Heartwood formation in young Eucalyptus bosistoana

By Gayatri Mishra, David Collings, Clemens Altaner, August 2016.

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Executive summary

Little is known about heartwood formation in young trees and published literature reports are based on heartwood of old trees. However, in the context of fast-growing short-rotation durable eucalyptus plantations, heartwood formation in young trees is important. There are indications that heartwood formation in young trees differs from that in old trees in the sense that the parenchyma cells in the transition zone, which synthesise the heartwood extractives, remain active for a longer period. This would result in a wider transition zone which is not ‘true heartwood’ – the part of the stem in which all parenchyma cells have died. The implication would be that the extractive content (and consequently wood quality) at the centre of the stem could improve over time in young trees.

The hypothesis that there is prolonged heartwood formation in young trees was tested by looking for living parenchyma cells in radial profiles of 6 year-old E. bosistoana trees. This was done by microscopy and different staining techniques. The observations revealed that 6 year-old E. bosistoana trees contained ‘true’ heartwood. In this tissue cell organelles (nuclie and vacuoles) and reserve material (starch) were absent; autofluroscence spectra indicated the presence of extractives; and vessels were blocked by tyloses.

As a consequence extractive content does not increase over time at the centre of 6 year-old E. bosistoana trees due to local synthesis and deposition of these compounds.

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