日本の枯死針葉樹材の分解度による材密度の推定

In systematic surveys for estimating dead wood biomass in forest ecosystems, the dead wood biomass is calculated by multiplying the volume by the wood density of the decay classes.In this study, we measured the mean wood densities in each decay class using dead wood provided by the non-commercial thinning of coniferous plantation forests.In addition, we compared the wood densities of 5 coniferous species (Cryptomeria japonica, Chamaecyparis obtusa, Larix kaempferi, Picea glehnii and Abies sachalinensis), three states (fallen logs, stumps, and snags), prefectures and diameter classes (5-10cm, 10-15cm, 15-20cm, 20-40cm) to clarify the effects of the parameters to variations in wood density.The mean wood density (g cm -3 ) measured from decay classes 1 to 4 were 0.33, 0.27, 0.19, 0.18 for C. japonica, 0.38, 0.31, 0.22, 0.17 for C. obtusa and 0.37, 0.32, 0.23, 0.13 for L. kaempferi.We found that in early decay classes, wood density significantly differs by tree species, diameter classes and states.However, in later decay classes, we cannot detect significant difference in the wood densities because of increased variations.The site effects on the wood densities did not show in early decay process among tree species.These results suggest that independent wood densities should be applied by tree species, diameter classes and state in decay class1and 2 for the accurate estimation of dead wood biomass in forest ecosystems.Then, we should also consider the variations of wood density by sites in decay class 3, 4 and 5 due to the different decay processes under different climate conditions.

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