| Xiangjiang River Basin is not only an important commodity grain base in China, but also one of regions that the urbanization speed is more prominent and the ecological environment change is more severe. In recent years, with the speeding up of industrialization and urbanization, traditional extensive economic model has not been a fundamental shift, leading to dramatic change of land use structure in Xiangjiang River Basin, and bringing about many serious ecological environmental problems, all of these problems have seriously threatened the sustainable development of the economy of Xiangjiang River Basin, and seriously endangered local human’s survival foundation platform. The net primary production(NPP) is an important indicator of terrestrial ecosystem, and it plays a key role on global change and ecosystem’s carbon balance. Through the research of spatio-temporal dynamics of NPP and its driving factors, it can objectively reflect the current situation,variation and spatial heterogeneity of ecological environment in Xiangjiang River Basin, so that it will provide the basis for further coordination an d improvement of ecosystem function, management and utilization of natural resources and the planning of main functional regions in Xiangjiang River Basin, effectively support the sustainable development of Xiangjiang River Basin and the construction of “Two Oriented Society” in Hunan province.Based on remote sensing data(DEM data, the average annual vegetation NPP data of MOD17A3 dataset, TM/ETM+ data), meteorological data, social-economy statistical data and other supplemental data, the spatial pattern of vegetation NPP and its spatio-temporal variation characteristics in Xiangjiang River Basin are quantitatively analyzed from sub-basin scale and pixel scale. Then this paper researches the driving factors of NPP from climate change and LUCC, the Pearson correlation coefficient method is used to analyze the relationship between climate change and vegetation NPP in Xiangjiang River Basin from whole sacle and pixel scale, and the Tupu analysis method is used to analyze the impact of spatio-temporal dynamics of land use on vegetation NPP from sub-basin scale,the upstream-middledownstream basin scale and whole basin scale.The main conlusions are as fellows:1) From the perspective of pixel scale, Higher NPP of research area appears in the mountain areas and huge Forest Nature Reserve zones in 2010, and lower NPP mainly distributes in urban and peri-urban areas, areas along Xiangjiang river, surrounding areas of lake; From the perspective of sub-basin scale, there are six sub-basins that NPP were more than 580 g C ' m-2' a-1, such as Zixihe, Juanshui, Lushui, Liuyanghe, Laodaohe,shixihe. And there are alos six sub-basins that the NPP are less than 520 g C'm-2'a-1, such as Chonglingshui, Yishui, Qishui, Lijiang, Binghu, Baihe. The Liuyang River Basin has the highes t NPP of 616 g C'm-2'a-1 in all sub-basins, while Binhu River Basin has the lowest NPP of 471 g C'm-2'a-1; From the whole basin scale, the NPP spatial pattern of Xiangjiang River Basin tends to decrease gradually from SE to WN in 2010, the average NPP of the whole basin is 549 g C'm-2'a-1, and region that NPP in 300~700 g C'm-2'a-1 accounts for about 91% of the total area.2) From the perspective of pixel scale, the variation of vegetation NPP mainly presents an insignificantly descending trend(66.57%) during 2000-2010, but the NPP in Changsha municipal districts declines extremely significantly; From the perspective of sub-basin scale, the annual NPP of each basin fluctuates within a certain range of values throughout the period, and they have the similar cha nge characteristics—downward trend. Although the NPP changes acutely in some particular time points, the relative variation rate of NPP is between 0.07 and 0.095 in each sub-basin, and overall inter-annual fluctuation is insignificant.3) In 2000-2010, the correlation coefficient between NPP and annual temperature is 0.132, and the correlation coefficient between NPP and annual precipitation is 0.318, the overall correlation is not significant. From the perspective of pixel scale, It displays a correlation between annual NPP and climatic factors in Xiangjiang River Basin, and some areas displays significantly. According to the correlation analysis between climatic factors and NPP, the climatic factors to some extent have some effect on NPP in Xiangjiang River Basin in Hunan province. Very few parts(8.91% and 5.38%) of NPP are greatly influenced by climate, most parts of NPP are not affected by climate change or the impacts are very small.4) In 2000-2005, land use change of upstream region is not obvious, and it has less effect on NPP, the rising of NPP mainly results from a wide range of forest vegetation that grows well. Because of the cropland conversion program and effective protection and management of a large area of forest vegetation, NPP of each basin in middle and downstream region increases. Although overall ecological environment has improved, but there is still a certain gap between the per capita NPP in Xiangjiang River Basin and the national per capita NPP(1921 kg C ' a-1), some region’s environmental problems can not be ignored(such as Changsha municipal districts); In 2005-2010, due to the increase of scope and speed of u rban expansion, cultivated land and Forest & grass land convert to construction land in most sub-basins in middle region, and they also lead to decline of the average NPP. In downstream region, because of further implement of cropland conversion program, parts of sub-basins’ annual average NPP has risen in 2010. Although the cropland conversion program to som extent promotes the rising of NPP in some areas, but as a result of intensive urban expansion, expanding of land use change and further disturbance of human activities, the overall annual average NPP and per capita NPP all decrease; In 2000-2010, because of the cropland conversion program, the average NPP in most of sub-basins in 2010 are higher than that in 2000. T he NPP is not all improving year by year, the average NPP of some sub-basins increases in the first five years, but decreases in the latter five years, which is mainly caused by the change of land use in different periods. The average NPP of whole basin in 2010 is 23 g C higher than that in 2000, and 13 g C lower than that in 2005, t he whole NPP showed the change characteristic in the process that first increased and then decreased, which is mainly caused by urban sprawl and cropland conversion program. In addition, the increase of population and human activities affect the NPP, aggravate the environmental carrying capacity. Although the average NPP in 2010 is higher than that in 2000, their per capita NPP are nearly equal. Throughout the study period, the ecological system service shows a potential descending trend.There may be following innovation in this paper:1)The spatio-temporal variation of vegetation NPP in Xia ngjiang River Basin and its relationship with climatic factors and LUCC are analyzed from sub-basin scale.2)The relevant research on NPP in Xiangjiang River Basin has not been reported, this paper makes a preliminary exploration and research on the basis of MOD17A3 dataset. |
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