Evaluation On Vegetation Net Primary Productivty Using Modis Data In Inner Mongolia

Vegetation cover is main body of the terrestrial biosphere. Net primary productivity (NPP) is defined as accumulative organic matters by green plants per unit of space and time. NPP not only reflect the plant community productivity directly for a certain natural environment but also fixing ability for CO2 by photosynthesis. It is a key component of the terrestrial carbon cycle and the basis of matter and energy cycle of terrestrial ecosystem. So it is widely used indices of C cycling in terrestrial ecosystems at local, regional and global scales. Inner Mongolia autonomous region, Situated on China's northern frontier, is the largest pasturing area in China. And it covers an area of 1.18 million square km and has abundant grassland resources. But because of the human negative activity and natural disasters, Inner Mongolia have been enduring many environmental problems such as land degeneration, vegetation decreases, desertification, loses of soil and water, frequent sandstorm attack and reduces of productivity in the second half of last century. These have threatened the sustainable development of this area and country's developing strategy for western China.Based on the CASA model and support of Geographic Information System, this paper studied the spatial and temporal dynamics of Inner Mongolian NPP for recent five years from 2002 to 2006 using MODIS/NDVI, ground meteorological data and classified vegetation data. From the study we can draw the some conclusions:1. There are clearly strong regional variations in Inner Mongolian terrestrial vegetation NPP. It increased from southwest toward northeast and has accord with the precipitation distribution basically. Regions of higher productivity are found in the eastern Da Xing an ling mountain area, western and southern broadleaf forest area of Chifeng and northern forestry of Xing An Meng. These regions can reach above 450gC/m2/yr. whereas the western desert area of A la shan Meng and water body have very small NPP values, it only ranges from 0―50gC/m2/yr, and many parts of it are seem to be 0.2. From this study, it can be drawn that from 2002 to 2006 (choose from April to August for each year), the terrestrial NPP of Inner Mongolia had a tendency to decrease. It is a short term fluctuation. This decrease may be caused by five month total precipitation. The precipitation of 2004, 2005 and 2006 (for five month) is lower than that of 2002 and 2003 clearly. Of course many other natural and social factors are also changing NPP fluctuation. The accumulated NPP from April to August for each year ranges from 0 to 751.72gC/m2/yr basically. NPP mean value ranges from 209.01 to 257.32gC/m2/yr. The total NPP ranges from 0.241 to 0.296Pg C/y(r1Pg= 1015g), and the average value is 0.273 Pg C/yr. The maximum NPP value is in 2002 and 2003, is 0.296 Pg C/yr and 0.295Pg C/yr respectively, the total NPP of these two years are seem to be like. And minimum is in 2004, the value is 0.241Pg C/yr. For the monthly variation, the NPP increases rapidly from April to July, and it reached the maximum value in July. The quantity of NPP in July and August is about 61.92% of the total in five month.3, For the NPP in different vegetation types, deciduous broadleaf forest has the highest NPP value as 516.45gC/m2/yr, the secondly is deciduous coniferous forest with 386.44gC/m2/yr and the thirdly are farmland, shrub and scattered forest region, the mean value is all above 300gC/m2/yr. Evergreen coniferous forest and grassland are 278.63gC/m2/yr and 262.05 gC/m2/yr respectively. And the minimum is the desert area with only 52.43gC/m2/yr. However, grassland has the highest total NPP value because of its large area, it has 1.52×1014gC/yr and occupy 55.68% of total NPP. Total NPP of the whole forest ecosystem is 6.03×1013g C/yr, and occupy 22.09% of total NPP. For the annual variation in the different vegetation types, NPP value of deciduous broadleaf forest and deciduous coniferous forest are increased, whereas evergreen coniferous forest, scattered forest, grassland, shrub and farmland are decreased. It may be caused by total precipitation...