Carbon cycling and sequestration in a Japanese red pine (Pinus densiflora) forest on lava flow of Mt. Fuji

Biometric-based carbon flux measurements were conducted in a pine forest on lava flow of Mt. Fuji, Japan, in order to estimate carbon cycling and sequestration. The forest consists mainly of Japanese red pine (Pinus densiflora) in a canopy layer and Japanese holly (Ilex pedunculosa) in a subtree layer. The lava remains exposed on the ground surface, and the soil on the lava flow is still immature with no mineral soil layer. The results showed that the net primary production (NPP) of the forest was 7.3 +/- A 0.7 t C ha(-1) year(-1), of which 1.4 +/- A 0.4 t C ha(-1) year(-1) was partitioned to biomass increment, 3.2 +/- A 0.5 t C ha(-1) year(-1) to above-ground fine litter production, 1.9 t C ha(-1) year(-1) to fine root production, and 0.8 +/- A 0.2 t C ha(-1) year(-1) to coarse woody debris. The total amount of annual soil surface CO2 efflux was estimated as 6.1 +/- A 2.9 t C ha(-1) year(-1), using a closed chamber method. The estimated decomposition rate of soil organic matter, which subtracted annual root respiration from soil respiration, was 4.2 +/- A 3.1 t C ha(-1) year(-1). Biometric-based net ecosystem production (NEP) in the pine forest was estimated at 2.9 +/- A 3.2 t C ha(-1) year(-1), with high uncertainty due mainly to the model estimation error of annual soil respiration and root respiration. The sequestered carbon being allocated in roughly equal amounts to living biomass (1.4 t C ha(-1) year(-1)) and the non-living C pool (1.5 t C ha(-1) year(-1)). Our estimate of biometric-based NEP was 25 % lower than the eddy covariance-based NEP in this pine forest, due partly to the underestimation of NPP and difficulty of estimation of soil and root respiration in the pine forest on lava flows that have large heterogeneity of soil depth. However, our results indicate that the mature pine forest acted as a significant carbon sink even when established on lava flow with low nutrient content in immature soils, and that sequestration strength, both in biomass and in soil organic matter, is large.