Effects of environmental factors on the color of sugi (Cryptomeria japonica D. Don) yellowish heartwood

The heartwood of sugi (Cryptomeria japonica D. Don), one of the most important planted trees in Taiwan, has a pleasant yellow, yellowish red to red color. Unfortunately, its attractive appearance is susceptible to discoloration after environmental exposure. This degradation is a significant defect that decreases the value of sugi products. The objective of the present study was to evaluate the effects of environmental factors on the color of sugi yellowish heartwood. We found that the color eventually turned to brownish black in the presence of moisture. Under the combined influence of light and oxygen the color of heartwood changed from yellow to reddish blue. The effect of light wavelengths on the discoloration of sugi yellowish heartwood was also investigated. After irradiation with light of wavelengths above 600 nm, the color of sugi yellowish heartwood changed significantly from yellowish to red. Our findings show that red color enhancement, and hence the economic value of sugi yellowish heartwood, can be achieved by irradiating with light of wavelengths above 600 nm.