Environmental effects on the color of sugi (Cryptomeria japonica D. Don) heartwood

Abstract

Sugi (Cryptomeria japonica D. Don) is one of the most important planted trees in Taiwan. The normal heartwood of sugi has a red to pinkish rose color. Unfortunately, this pleasant appearance is susceptible to discoloration after environmental exposures. This discoloration is a serious defect that decreases the value of sugi products. The objective of this study was to investigate the effects of environmental factors such as moisture, oxygen, and lights of different wavelengths on the discoloration of sugi. The results show that under the combined effects of light and oxygen the color of heartwood changes from red (or rosepink) to bluish green. The color further darkens and eventually turns to black with the presence of moisture. As for the effect of light wavelengths on the discoloration of sugi heartwood, it was found that the red color was enhanced after being irradiated with light of wavelengths above 600 nm. Bothδa^* andδb^* values increased significantly as a result of such exposure.