Resistance of Plantation Hinoki to Fungal Attack

Abstract Hinoki ( Chamaecyparis obtusa ) is among the most common tree species in Japan and is valued for its superior mechanical properties and durability. Extensive establishment of hinoki plantations has resulted in an excess supply of this timber, prompting a desire to export, particularly to the United States. Although the timber has excellent mechanical properties, concerns have arisen that the heartwood will be less durable as a result of silvicultural practices to enhance growth rates. Research has shown declines in heartwood durability of some second-growth species compared with old growth of the same species, but research is lacking regarding this phenomenon in hinoki. This study assessed heartwood extractives content in relation to the resistance of second-growth hinoki heartwood from four regions in Japan to decay by Rhodonia placenta , Gloeophyllum trabeum , and Trametes versicolor in laboratory soil-block tests. Heartwood from all four regions was highly decay resistant when exposed to the selected test fungi, with levels comparable with western redcedar ( Thuja plicata ). Hinoki from Shikoku was most resistant to G. trabeum (4.73% mass loss), whereas timber from Kyushu was most resistant to R. placenta (6.72% mass loss) and T. versicolor (0.58% mass loss). Heartwood durability correlated poorly with extractives content. These results support the continued classification of hinoki as highly resistant to fungal attack, highlighting its potential for broader adoption beyond Japan.