Colour of larch heartwood and relationships to extractives and brown-rot decay resistance

Abstract

Larch heartwood is appreciated for its good mechanical properties, its colour and its texture, and it is often used outdoors because of its natural durability (decay resistance). In this study the colour of larch heartwood was studied in relation to extractives and decay resistance, with the aim to estimate durability of larch heartwood from its colour. On a total of 293 trees colour in the CIE L*a*b* space (L* lightness, a* red/green axis, b* yellow/blue axis), extractives content (acetone and hot-water extractives, amount of phenolics) and the brown-rot decay resistance were determined. For calculating the relative decay resistance (x), mass loss after inoculation for 16 weeks with two fungi [Coniophora puteana (Schum.ex.Fr.) Karst., Poria placenta (Fr.) Cke, European standard EN 113] of larch heartwood samples was compared to Scots pine (Pinus sylvestris L) sapwood reference samples (EN 350-1). Different species [Japanese larch (Larix kaempferi Lamb.), Hybrid larch (Larix deciduax L. kaempferi) and European larch (L. decidua Mill.)], provenances and age classes (38-year, >150-year) were included. Japanese larch heartwood turned out to be significantly more reddish (higher a*-values) compared to the European larch provenances. Reddishness of the hybrids was intermediate. The red hue (+a*) was strongly correlated with the amount of phenols (r=0.84) and decay resistance (r=0.63) and therefore suitable for prediction of both parameters. The results suggest that colour measurements of larch heartwood could be of benefit in tree breeding programs and for an optimised utilization of larch timber.

Wood colour variation in sapwood and heartwood of young trees of Tectona grandis and its relationship with plantation characteristics, site, and decay resistance

“…SAS (SAS Institute Inc.) and STATISTICA 6.0 (Statsoft Inc.) programs were used for the statistical computations. For example, redness (a * ) and lightness (L * ) are correlated with extractive content, while yellowness is primarily related to the photochemistry of the major wood components, especially lignin (Gierlinger et al, 2004).…”

“…IV). As was mentioned above, the difference in colour between heartwood and sapwood is due to the process of heartwood formation, with the extractives produced accumulating in the heartwood, resulting in colour (Gierlinger et al, 2004). The process depends on several factors, such tree age, soil composition and location with in a tree.…”

“…The change in colour from sapwood to heartwood is due to the synthesis and accumulation of extractives during heartwood formation. Variation in colour within heartwood is due to oxidation and polymerization reactions that take place as wood ages (Gierlinger et al, 2004).…”

“…It has been used to measure colour variation and its relation to plant genetic sources (Sotela et al, 2008), effect of drying on colour (Möttönen et al, 2002), relationship between colour and decay resistance (Gierlinger at al., 2004), and effect of thermal treatment on wood colour (Johansson and Morén, 2006).…”

Alteração da cor da madeira de teca por tratamento térmico

“…O teor de extrativos apresentou uma correlação significativa com a luminosidade (L*) e a tonalidade vermelha (a*), indicando que as madeiras mais escuras (menor L*) e com mais pigmento vermelho apresentam um maior teor de extrativos (Marinonio, 2011). Estes resultados são similares àqueles encontrados por Gierlinger et al (2004), os quais observaram que a* e L* da madeira de Larix decidua Mill apresentaram uma correlação com o teor de extrativos. Varga & Van Der Zee (2008) avaliaram o efeito do tratamento térmico nos parâmetros colorimétricos da madeira de Robinia pseudoacacia e Intsia bijuga, e observaram que a alteração da cor é altamente dependente da espécie.…”