Tomohiro Nishizono, Eiji Kodani, Hidesato Kanomata, Kazuo Hosoda, Keiko Fukumoto, Yosuke Yamada and Tomomasa Amano: Optimal harvest age based on timber production profitability of Japanese cedar-planted forest: analyzing data from long-term experimental monitoring plots in the Japan Sea side of the Tohoku region, Northern Japan. Jpn. J. For. Plann. 55: 77~93, 2022 We analyzed data from 29 long-term experimental monitoring plots installed in Japanese cedar (Cryptomeria japonica D. Don)-planted forest in Northern Japan to examine the optimal harvest age based on timber production profitability. We investigated the change in forest rent (FR) and internal rate of return (IRR) with changing harvest age. Under current economic conditions, the indexes in half of the plots were typically negative for all harvest ages. We could not determine the optimal harvest age using the indexes; however under current economic conditions, with subsidies, the indexes in all plots were positive above a certain harvest age. Under this condition, FR and IRR reached their maximums in 72-102 years (mean, 87.3 years) and 58-97 years (mean, 80 years), respectively. The relationship of harvest age on timber production profitability for FR indicated that older harvest ages are suitable for the examined forests. Also, the relationship for IRR indicated that for forests with low productivity older harvest age is suitable, and that for forests with high productivity, thinning practice can change and control the optimum harvest age (earlier and older).
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