Quantifying phenotypic variation in wood colour in Acacia melanoxylon R.Br.

Abstract

Australian blackwood (Acacia melanoxylon R.Br.) is a high-quality appearance-grade hardwood species native to eastern Australia. Heartwood colour varies from pale cream, straw, golden-brown, red-brown and walnut, with prominent annual growth rings; sapwood colour is generally pale cream. This wide colour range in heartwood is associated with both between- and within-tree variation. Colorimetry was used to quantify the phenotypic range and variation in heartwood and sapwood colour in stem cores taken from 19-year-old trees belonging to 16 open-pollinated families. The trees were located in three progeny trials in northern Tasmania, Australia. Cores were also visually classified into four colour and four colour variability classes. Both heartwood and sapwood had very wide colour ranges and high between- and within-tree colour variation. Analysis of variance showed that colorimetry can be successfully used to quantify heartwood colour and colour variability, with lightness and redness differing significantly between visual colour grades, while within-tree maximum colour difference (maximum ΔE76) was the best derived colour trait in discriminating grades of heartwood colour variation. Correlations between within-tree sapwood and heartwood colour were significant, but moderate to low, precluding the possibility of assessing heartwood colour in standing trees by measuring sapwood colour.