Japanese Cedar (Cryptomeria Japonica D. Don) Plantations Are the Most Common Type of Plantation

Abstract

The Kyoto Protocol came into effect in February 2005. To reduce Japan’s carbon emissions, the Japanese government plans to thin abandoned plantation forests to promote carbon fixation by the regrowth. Although thinning can increase the amount of carbon fixed by the growth of the remaining trees because of higher availability of light, decomposition of forest floor carbon might be stimulated because soils become warmer. Japanese cedar (Cryptomeria japonica D. Don) plantations are the most common type of plantation forest in Japan. Accurate estimation of soil respiration in these forests is important in assessing their contribution to the carbon budget and developing suitable management plans. Thus, this study was designed to understand the effects of thinning on the carbon budget through field measurements before thinning (year 0) and 1 and 2 years after thinning in a 27-year-old Japanese cedar forest in the temperate climate zone. An experimental site (30 m × 30 m) on the southern slope of Mt. Yunodake was divided into two plots, thinned and unthinned. Soil respiration rates, soil temperature, and soil moisture were measured, and every tree was surveyed. Soil respiration rate increased exponentially with soil temperature in the thinned plot. The emissions of soil carbon in the thinned plot were 3.99–5.29 (year 0), 4.11–5.46 (year 1), and 4.06–5.39 (year 2) t-C ha–1 year–1. Slight decreases may have been due to decreased root respiration and input of litter. The amounts of carbon fixed in the thinned plot were 11.87 (year 0), 8.65 (year 1), and 9.90 (year 2) t-C ha–1. The annual carbon budgets in the thinned plot were therefore 6.58 to 7.88 (year 0), 3.19 to 4.54 (year 1), and 4.51 to 5.84 (year 2) t-C ha–1 year–1. Thinning changed the emission of carbon from the soil and the amount of carbon fixed by trees. The annual carbon budget in the thinned plot was greatly decreased in 1year after thinning, but by 2 years the carbon budget had begun to increase, suggesting that this forest will become a greater carbon sink in the future. The long-term effects of thinning are still unknown and require additional years of measurement.

Keywords: soil respiration rate, thinning, Japanese cedar, soil temperature, carbon budget