| An increasing attention has been focused upon carbon storage and its variation of terrestrial ecosystem which is always being the important point in the study on climate and environment change at a global scale. Moreover, Changing of land-use acts leading by human activities and natural factors are the key driving elements that affects terrestrial ecosystem carbon cycle. unreasonable land utilization, such as deforestation, reclamation of cultivated land and town construction etc, make lots of natural ecological process alert, thus affect the vegetation carbon significant changes. Net Primary Production (NPP) is the net amount of carbon captured by land plants through photosynthesis, meanwhile, it is also the key component of surface carbon cycle. Furthermore, The net primary productivity of the vegetation can not only reflect the capacity which the vegetation fixes on atmospheric CO2 but is also an indicator for assessing the terrestrial support ability and evaluating the sustainability of terrestrial ecosystems. Xilingol is the typical grassland range in our country and the vulnerability of grassland ecosystem and sensitivity to the climate change has extremely easy to causing the change of surface cover due to human activities. So, it is apply to evaluates the bearing capacity of xilingol ecosystem by research of the dynamic response of the vegetation's primary productivity for land use change and provides the theoretical foundation to the sustainable development and utilization of grassland resources.In this paper, it uses solar energy utilization rate of the CASA model as the foundation, and uses MODIS remote sensing data, temperature, precipitation, and different vegetation types as important parameters of model to estimate Xilingol terrestrial vegetation net primary productivity from 2000 to 2013 years. At the same time, it Analyzes the space-time dynamic change with vegetation NPP. It is also Combined with the 4 time interval of the land use data, finally quantitative calculate different loss value of net primary productivity, Then analyzed the influence of land use change on net primary productivity. Through the analysis, the following conclusions:(1) During 2000-2013 years, The average NPP of vegetation showed an increasing trend in Xilingol and the increase rate is 4.54/a. Among them, In 2003 and 2012, the average of values are much higher, which are 301.48gC/m2/yr and 49.34gC/m2/yr. Minimum average NPP appeared in 2001 and 2007, which are 205.88gC/m2/yr and 200.77gC/m2/yr. Accumulative total NPP is consistent with the unit average NPP change. From the seasonal change trend, the mean NPP of spring, summer and autumn increased, the rate of increase in summer NPP maximum (3.79/a), which is much lower than annual increasing rate. From correlation analyses between NPP and climate factors, the changes of NPP is mainly affected by precipitation amount and temperature change, which keep a negative relationship with the avarage annual temperature and it has outstanding positive relevance with the precipitation. Thus, the precipitation is the main factor that leads to the Inner Mongolia terrestrial vegetation NPP increases, but the temperature limit the NPP's increasing to a certain extent.(2) From space distribution about NPP during 2000-2013 years, the East is High while the West is low. The distribution trend, decreasing from northeast to southwest, consistent with the change trend of hydrothermal condition and distribution of vegetation form in this region. The total area of the entire study area accounted for 93.3% showed an increase trend. However, the significantly reduced area is very small, the total area of the study area 7.7%. From the distribution of seasonal trend of NPP spatial variation, the increasing area of seasonal NPP is larger than the decreasing area. Among them, the area of summer NPP, showing a significant increasing trend, is the largest, which account for the total area of the whole study area 91.76%. While the area of autumn NPP, showing a significant decreasing trend, is the largest, which account for the total area of the whole study area 17.78%.(3) Firstly, the grassland is always ranked first, account for the total area of the whole study area during the 2000-2013 years on the distribution scale, which is Focusing on the increasing trend in 14 years, especially during the 2005-2009, is 3179.75 km2 for its transfer to cultivated land and unused land mostly; The range of forest land is more greater between 2009-2013 (256.58 km2), which transited from grassland showing that succeed with afforestation in Xilingol region; At the same time, the cultivated land area keep decreased by 961.71 km2 during the 2005-2009. Apparently, those variation trend has a direct revelance with corresponding measures of ecosystem protection and projects. With rapid changing of economy and increasing of population, it is promotes the process of urbanizition, expanding of county town, then makes construction land in a large degree, which range is increased 545.9 km2 during the 2009-2013 significantly and it is converted by grassland. What's more, area of unused land decreased continuously, which transited to grassland and water in a large degree, Showing that reserving sources can received the availably exploitation. For water area, its decreased to unused land had great relationship with construction projects and lower rainfall.(4) During the 14 years, the permutation of average NPP in Xilingol region is woodland> cultivated land> grassland. Woodland as the perennial woody plants, can be a definitive storage of organic matter in the forest, is bigger to the contribution of the terrestrial ecosystem carbon storage. Focusing on the variation trend, cultivated land and forest land area decreased at first and then increased afterwards, but the change is not be equal completely. Compared with the 2000-2005 years, the reducing rate is significantly faster from 2005-2009. The average NPP of grassland showed a decreasing trend between 2000-2005 years and it was continues to increased during the 2009-2013 Especially in 2009 ? 2013 years. For the conversion among cultivated land, forest land, grassland and other land, the cumulative vegetation NPP were increased of 0.026 TgC?0.037 TgC and 0.38 TgC in Xilingol region. Benefits of grassland NPP is significantly increased than forest land and farmland, mainly from the conversion of unused land. At the same time, grassland, forest land and some kind of transformation makes the NPP decreased, but the losses is little. Forest land turn to waters and construction land, which leading to the NPP lost both 0.28 x 10-4 TgC and 2.36 x 10-4 TgC. The main reason leading to loss of NPP on a large scale was that grassland turn to the construction land, which is 53.55×10-4TgC. Grassland as the main land use types in Xilingol area during the 14 years, its increasing of area is the primary causes leading to growing of vegetation NPP in the study area. However, there are many driving forces to decrease the vegetation NPP in Xilingol region that extending of stock raising by factors of population growth and economies, exploitation of coal resources and burst of urban expansion can tales the grassland in a large scale. Furthermore, the accelerating the development of economy and urbanization and appropriate returning farmland to forest, afforestation, the coordination of regional resources development and ecosystem protection is an important ways to balance with the terrestrial carbon reserves.(5) From distribution of internal changing of grassland, firstly, the middle coverage grassland is an internal principal type in Xilingol region, which takes 43.38% of total area of grassland. Secondly, the high coverage grassland takes 43.38% of total area of grassland. Finally, the proportion of low coverage grassland area is minimal, which takes 13.91% in whole grassland area. The high coverage grass continues to increase, which area is converted by the middle coverage grassland; Focusing on the increasing trend, both middle coverage grassland and low coverage grassland has increased at first and then reduced afterwards and the decreasing rates of low coverage grassland is much bigger than middle coverage grassland is. Among of them, the middle coverage grassland turn into the high coverage grassland and the low coverage grassland turn them to the middle coverage grassland. Variations in different coverage grassland area from 2009 to 2013 is the largest, which is the same trend with NPP variation caused by transformation of different coverage grassland. Different coverage grassland resulted in losses of grassland NPP in 2000-2005,which is 0.02TgC, and with the middle coverage grassland turn into low coverage of grassland is the main decreasing reason of NPP. At the same time, the grassland NPP lost about 0.029 TgC during 2005-2009, then the high coverage grassland turn into middle coverage of grassland is the driving factor. The conversion of different coverage grassland has bringing about profits of grassland NPP (1.816 TgC), and the high and middle coverage grassland turn into high coverage of grassland is the primary cause. In the whole period of research, the inter conversion for various types of grassland has leading to increment of NPP and it is 2.614TgC. The increase of high coverage grassland is the main source of grassland NPP at studying process. With the middle coverage grassland turn into high coverage of grassland, it has a greatest contribution rate to accumulated NPP of vegetation in Xilingol region. Obviously, the growing states of grassland was improved in large scale in Xilingol area during the 14 years. Specifically, the continuing increase of high coverage grassland area can get more benefits to vegetation accumulated NPP. |
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