On The Spation-temporal Simulation Of Forest Ecosystem Net Primary Productivity And Net Ecosystem Productivity In Fujian Province

Forest ecosystems are being paid with growing attention because of their importance for mitigating global environmental change. Forest ecosystems play a significant role in the global carbon budget, and their carbon fixation ability contributes directly to the decrease of the increasing rate of atmospheric CO₂ concentration and to protect biosphere from global warming. As a key component of carbon cycle, net primary productivity (NPP) of forest ecosystem reflects the net amount of carbon fixed by forest ecosystem over time. As the difference between NPP and heterotrophic respiration (R_h), net ecosystem productivity (NEP) of forest ecosystem explicitly describes the character of carbon budget. It is critical to estimate forest ecosystem's NPP and NEP spatial and temporal pattern under the background of global change at regional scale, and the result will benefit to understand the carbon dynamics within the atmosphere-vegetation-soil continuum and the response of terrestrial ecosystem to future climate warming.I chose Fujian province as my study area, which has the highest forest coverage in China and locates in subtropical zone where carbon budget study received little attention. Based on '3S' technologies (GIS, RS, GPS), this study applied two kinds of carbon cycle models (ecological process model and remote sensing-based parametric model) to explore the spatial and temporal characteristics of net ecosystem productivity of Fujian forest ecosystems at regional scale. The two models agreed on the NPP of Fujian' forest ecosystem in 2005 both spatially and quantitatively, and their estimates of NPP agreed quite well with those reported by previous investigators which was summarized from direct field measurements in subtropical forest ecosystems.The results of Biome-BGC model showed that the annual mean NPP of Fujian's forest ecosystem was 759.63 g C m^-2 a^-1 from 1991 to 2005, the average NPP per forest area for the same period was 2.04×10⁸ g C a^-1 ; for the NEP, annual mean and average value per forest area was 43.94 g C m^-2 a^-1 and 1.17×10⁷ g C a^-1 respectively. There were obvious regional variations in the distributes of NPP and NEP, with higher NPP and NEP in the two mountains areas of Fujian province where elevation is relative high and little influence by anthropogenic activities were found. Combined with regional climate model estimate, I predicted the possible future changes of NPP and NEP for Fujian's forest ecosystems. For the whole province, doubled atmospheric CO2 concentration combined with climate change will cause the NPP and NEP of forest ecosystem in Fujian to increase by 11% and 245% respectively.Based on MODIS data in 2005 and corresponding spatial weather data yield by spatial interpolation, I estimated NPP of Fujian's forest ecosystems in 2005 using the remote sensing-based parameterized model. The results indicated that the mean value of Fujian province forest ecosystems NPP was 818.585 g C m^-2 a^-1, total NPP was 2.19×10⁸ g C a^-1, and there were two significant peaks of NPP during the year.