Global Mapping of Terrestrial Primary Productivity and Light-Use Efficiency with a Process-Based Model

The carbon dynamics of terrestrial ecosystems was globally simulated with a mechanistic model, Sim-CYCLE, at a spatial resolution of 0.5° × 0.5° in longitude and latitude. Gross photosynthetic production (GPP), net primary production (NPP), carbon storage, absorption of photosynthetically active radiation (APAR), and light-use efficiency (LUE) were addressed. Assuming an equilibrium state under the present environmental conditions, Sim-CYCLE estimated the annual global GPP and NPP as 124.7 and 60.4 Pg C yr–1, respectively. Based on the estimated APAR of 191.3 × 1021 J, the annual average biospheric LUEs for GPP and NPP were calculated as 0.652 and 0.315 g C MJ–1, respectively. Global maps obtained by the model simulation illustrate the heterogeneity of ecosystem functions over the land surface, from tropical rain forests to polar deserts. There was a significant correlation between the estimated APAR and NPP (r2 = 0.62, p < 0.0001); such model simulations and analyses should be effective for interdisciplinary research with remote sensing, in which a linear relationship between APAR and NPP is frequently assumed.