Carbon stock estimates for sugi and hinoki forests in Japan

Abstract

Forest inventory data are widely used for broad-scale quantification of forest carbon budgets. Such data usually represent forest wood volume (m 3 ha-1), which needs to be converted to biomass carbon value (Mg C ha-1) for carbon stock estimates. Our main objective is to estimate the carbon stock for all sugi (Cryptomeria japonica D. Don) and hinoki (Chamaecyparis obtusa Endl.) plantations in Japan on the basis of age-class-based forestry statistics. To achieve this purpose, we estimated regional wood volume accumulation and biomass allocation over time for sugi and hinoki forests to calculate and map the carbon stock in all sugi and hinoki plantations in Japan on the basis of forestry statistics. Hinoki forests showed smaller accumulation of volume than sugi forests from ca. 25 years old to maturity; the accumulation of wood volume per hectare at 80 years old was <600 m3 ha-1 for hinoki and >600 m3 ha-1 for sugi. Patterns of biomass allocation to forest components varied by forest type; the proportion of branch biomass in 0-20-year-old hinoki forests is 5-10% larger than that of sugi; the proportion of stem biomass in the same age range is 5-10% smaller than that of sugi; the ratio of roots was approximately constant as its average value, 20.4% for sugi and 22.7% for hinoki. The ratios of total biomass to bole biomass (i.e., expansion factor (EF), Mg total biomass Mg-1 bole biomass) decreased with increasing age, and became nearly constant after 30 years old for sugi and hinoki. The mean EFs were the same for the two forest types, with a value of 1.72 Mg Mg -1. Our results suggest that sugi and hinoki plantations in Japan, respectively, store 346.4 × 106 and 139.2 × 10 6 Mg of carbon, with an area-weighted mean of 76.81 and 58.01 Mg C ha-1. High amounts of carbon stock in both sugi and hinoki are located in the southwestern part of Japan. © 2003 Elsevier Science B.V. All rights reserved.