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To the heart of the matter - heartwood content in totara

Authors: Greg Steward
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2019, Issue N.Z.J.For. 64(2) 2019, pp 37-41, Aug 2019
Publisher: New Zealand Institute of Forestry

Abstract: The amount of durable heartwood present in submature New Zealand totara (Podocarpus totara D.Don) is not well understood, as it has been difficult to predict or accurately identify. Durability is seen as one of the value propositions for harvesting relatively young totara from farm sites in the Northland region. With the objective of identifying tree or site characteristics related to heartwood content, a dataset of observations of heartwood content has been compiled from geographically separated totara stands. The findings on heartwood content found in 420 totara from 15 natural second-growth and six planted stands are presented. Heartwood, based on colour, was identified in almost 70% of totara that were between 35 and 127 years old and from 10 to 87 cm in diameter. Crosssectional discs from log ends were better for identifying heartwood content than 5 mm bark-to-pith increment cores. Small diameter totara (<20 cm) that averaged over 70 years old were found to contain small quantities of heartwood when measured from cross-sectional discs. Conversely, trees with no heartwood were found in all diameter classes from 10 cm to almost 70 cm. Totara in planted and natural stands displayed similar levels of heartwood content. The presence and quantity of heartwood was highly variable, although variability decreased markedly with increasing stem diameter. There was greater certainty in predicting heartwood content at the population and stand level than for individual trees.