Estimating forest biomass using allometric model in a cool-temperate fagus crenata forest in the appi highlands, Iwate, Japan

To estimate forest biomass and productivity in a cool-temperate deciduous hardwood forest of the Appi Highlands in northern Japan, we developed allometric equations for estimating relationships between size-related variable (stem diameter at breast height (dbh)) and biomass of leaves, branches, stems, and roots for Japanese beech (Fagus crenata) trees. This is one of the most typical species growing in the cool-temperate zones of Japan. At the present study site, Japanese beech trees comprised 75% of all forest trees (1,666 trees /ha in 2012) and 80% of the sum of basal areas for all species. Twelve trees of various sizes were comprehensively harvested to measure tree biomass at the study site. Allometric equations developed for all parts of biomass as a function of dbh showed high correlations (Adjusted R**2 = 0.92-0.99). Using two independent external datasets, validation results for stem biomass estimates were quite good although those for branch, leaf, and root biomass were not as accurate because of relatively large SEP (standard error of prediction) of branch and leaf biomass estimates for the validation dataset and underestimation of leaf and root biomass for small-sized trees. Insufficient accuracy of those biomass estimates may not have hindered the accurate estimation of forest biomass in the Appi Highlands because stem biomass was a main component of forest biomass and the low accuracy estimates only involved inaccuracies in the estimates for some of small-sized trees (dbh < 10 cm). Forest biomass in the Appi Highlands was estimated to be 343 t /ha using the equations developed here. This value was slightly higher than average values of Japanese beech forest in previously published biomass data. Results of the present study will be helpful for advancing further studies on the determination of annual changes in forest productivity and carbon dynamics in Japanese beech forests in the Appi Highlands.