Model Estimates of Global Carbon Flux between Vegetation and the Atmosphere

The net primary productivity (NPP) of global terrestrial vegetation is estimated by an Atmosphere-Vegetation Interaction Model (AVIM). AVIM consists of two intercoupled components: phys ical processes, involving water and energy transfer among soil, vegetation and the atmosphere at the land surface and eco-physiological processes, ie. photosynthesis, respiration, dry matter allocation, littering, phenology. Globally vegetation is classified into 13 types and soil texture is classified into 6 types. The esti mated NPP for different vegetation types at 1637 sites are validated with the observed data provided by EMDI. The main results of NPP estimation show that global averaged NPP is 405.13 g C m-2yr-1 varying from 99.58 g C m-2yr-1 (tundra) to 996.2 g m-2yr-1 (rainforest). Global total annual NPP is about 60.72Gt Cyr-1, in which the maximum part, about 15.84 Gt C yr-1, accounting for 26.09% of the total is contributed by tropical rainforest. The maximum carbon sink occurs in the temperate region of the Northern Hemi sphere. The global spatial and seasonal distribution of terrestrial NPP is estimated reasonably.