Forest ecosystems are expected to contribute to sequestering atmospheric CO2 as strongly related to global warming. In recent research activities on forest productivity, much effort have been made to understand carbon stocks and carbon flow in various forest ecosystems. This paper overviews recent knowledge of carbon sequestration into forest ecosystems, then discusses the role of carbon cycling in forest ecosystems. Ordinarily managed sugi（Crypromeria japonica）plantation forests in Japan generally sustain biomass carbon of about 150 ton/ha at around 100 years of age. Under preferred environmental conditions, massive forests with gigantic tree height and biomass could rarely appear. It is reported that the biggest forest in biomass carbon is 360 ton/ha in Japan, whereas 1,730 ton/ha in California, USA. Highest biomass values could be referred to the potential of forest carbon stock. In tropical rain forests, photosynthesis shows higher performances because of preferable conditions with moist and warm environment, which promotes carbon sequestration into forest biomass compared with other forest ecosystems. However, due to the higher decomposition rate, the soils in tropics show lower carbon stocks. On the contrary, although boreal forests sustain fewer carbons in biomass, the soil carbon contents exhibit higher values than tropical rain forests because of lower decomposition rate of soil organic matter under lower temperature. Evaluating carbon sequestration into forest ecosystem, carbon flows and carbon stocks in ecosystems is essential to be quantified as influenced by environmental conditions such as temperature, moisture, water and nutrient availability. In addition, we should quantitatively understand and model the ecophysiological processes in forest dynamics and carbon cycles in order to explain the variation of carbon allocation and realized carbon stocks in various forest sites.
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