Wood properties of Japanese lilac (Syringa reticulata) that promoted selective use in prehistoric Hokkaido

Abstract It is known that in prehistoric Hokkaido, the wood of the Japanese lilac ( Syringa reticulata ) was used as structural material; for example, in pillars and rafters of dwellings. This suggests that Japanese lilac wood has useful properties, such as high strength and strong decay resistance. However, few studies have been conducted on the wood strength and decay resistance of this species. The present study was undertaken to evaluate the strength and decay resistance of Japanese lilac wood and reveal the factors responsible for its general use in prehistoric periods. The results of mechanical tests show that the strength of the wood, as quantified through several different indices, is above moderate. In particular, static modulus of elasticity and modulus of rupture of Japanese lilac wood were higher than those of other species commonly found in Hokkaido. Regarding decay resistance, the mass-loss rate was only 1.6% after incubation with Trametes versicolor for 60 days. We conclude that Japanese lilac is a suitable material for structural materials in which high bending strength is desired. In addition, its extremely high decay resistance makes it conducive to long-term use outdoors. Overall, the results of this study indicate that the extremely high decay resistance and excellent bending strength of Japanese lilac were the main reasons for its use in prehistoric periods.