Evaluation on vegetation net primary productivity using MODIS data in Inner Mongolia

Abstract

Vegetation net primary productivity (NPP) is a key component of the terrestrial carbon cycle. It is always used as an index of C cycling in terrestrial ecosystems at landscape and regional scales. Based on the CASA model, this paper studies the spatiotemporal dynamics of Inner Mongolian NPP from 2002 to 2006 (choosing from April to August in each year for analysis) using MODIS/NDVI, ground meteorological data and vegetation type data. The result shows that the terrestrial NPP of Inner Mongolia has a tendency to decrease from 2002 to 2006. The NPP value varies from 0 to 751.72gC/m 2 /yr, Mean NPP ranges from 209.01 to 257.32gC/m 2 /yr. The average total NPP of these five years is 0.273 Pg C/yr (1Pg= 10 15 g) ranging from 0.241 to 0.296Pg C/yr, which is about 8.69% of the total terrestrial NPP in China. The variations of NPP in different vegetation types are significant. The deciduous broadleaf forest has the greatest mean NPP value of 516.45gC/m 2 /yr, the deciduous coniferous forest goes next with that of 386.44gC/m 2 /yr, and thirdly the agricultural vegetation, shrub and open forest region with that all above 300gC/m 2 /yr; Evergreen coniferous forests and the grassland are 278.63gC/m 2 /yr and 262.05g C/m 2 /yr respectively. The grassland has the greatest total NPP of 1.52×10 14 g C/yr owing to its largest area, and the whole forest ecosystem has that of 6.03×10 13 gC/yr, occupying 55.68% and 22.09% of total NPP of Inner Mongolia respectively. NPP in all vegetation types varies significantly in previous five years, with deciduous broadleaf forest and deciduous coniferous forest increasing, whereas the other types have decreased.