Spatial distribution of carbon balance in forest ecosystems across East Asia

The objective of this paper is to clarify what kind of environmental factors that regulate net ecosystem production (NEP), gross primary production (GPP), and ecosystem respiration (RE) in forest ecosystems across East Asia. Study sites were widely distributed and included diverse ecosystems, such as evergreen and deciduous, coniferous and broadleaf, planted and natural forests, from subarctic to tropical zones. We measured NEP using the eddy covariance technique at 13 forest sites in East Asia. Annual values of GPP and RE are simply regulated by annual mean air temperature across East Asia. There is a clear linear relationship between annual GPP and annual mean air temperature because the air temperature influences both growing period length and the seasonal variation of the maximum photosynthetic capacity, which, together, regulate the annual GPP. On the other hand, there is a strong exponential relationship between annual RE and annual mean air temperature on an East Asia scale, which is quite similar to the relation obtained on a canopy scale. The dependency of annual RE on air temperature on the East Asia scale was similar to that of monthly RE on air temperature on an individual site scale excepting for temperate larch and mixed forests in northern Japan. The reason why the relation is simple is that severe stress, which affects GPP or RE, is small in East Asia. The present study suggests that RE is sensitive to non-climate environmental factors when compared to GPP, thus the annual RE-air temperature relationship is more scattered than the annual GPP-air temperature relationship. The NEP is small at high latitude, relatively large at mid-latitude, and scattered at low latitude. As a whole, the NEP is more influenced by RE than GPP in East Asia. Compared to North America and Europe, the increase in the ratio of GPP to air temperature is slightly higher in East Asia. One of the possible reasons for this is that GPP in East Asia is not exposed to severe environmental stresses, such as summer drought.