| Vegetation net primary productivity(NPP) is the amount of carbon fixed by plants each year through photosynthesis and an important indicator of ecosystem response to climate change. Not only it can reflect production capacity of the plant community in the natural environment under the condition, but also it is an important part of the terrestrial carbon cycle. As one of the important means of vegetation net primary productivity of study using the model to estimate net primary productivity of terrestrial ecosystems, has been widely used in regional and global scale carbon cycle research. At present, the vegetation NPP research is still one of the important content of global change research, especially the research on the regional vegetation NPP. Qilian Mountains is an important ecological region in northwest of China. Simulating vegetation net primary productivity in the region and analyzing its variation in time and space have a very important significance for understanding regional carbon cycle, and they can provide a scientific basis for the utilization of natural resources and the rational development of Qilian Mountains area. In this paper, these questions are studied based on the GLC2000(Global Land Cover 2000) of the global land cover data, Global soil texture data, Global climate data and IPCC greenhouse gas emission scenarios special report SRES(Special Report on Emissions Scenarios) B1 scenario of climate data, using AVIM2 model to simulated nearly 50 years(1958~2008) and the future of recent 40 years(2015~2055) vegetation net primary productivity in Qilian Mountains, then using Arc GIS and Excel made statistical analysis of space and time to the results. The preliminary results of the study are as follows:(1) From 1958 to 2008, the vegetation NPP in Qilian Mountains presents increasing trend from the northwest to southeast in space. The vegetation NPP in Qilian Mountains presents wavy increasing trend with the increase rate of 0.718g·m-2·a-1(C) and the range of 90~160 g·m-2·a-1(C). Vegetation NPP changes in different seasons are wavy increasing trend in Qilian Mountains, but there are differences in trends. Summer vegetation NPP increase rate of 0.414 g·m-2·a-1(C) is the highest, followed by autumn and spring, respectively 0.185 g·m-2·a-1(C) and 0.1 g·m-2·a-1(C), the smallest in winter is 0.016 g·m-2·a-1(C).(2) From 1958 to 2008, there are some significant spatial differences of vegetation NPP changes in different periods in Qilian Mountains. From 1958 to 1968, Vegetation NPP reduced area accounted for 33.01% of the total area, increased area accounted for 15.3% of the total area. From 1968 to 1978, vegetation NPP reduced area accounted for 1.83% of the total area, increased area accounted for 33.92% of the total area. From 1978 to 1988, vegetation NPP showed a trend of increase overall, and increased area accounted for 55.2% of the total area. From 1988 to 1998, the vegetation NPP also showed an increasing trend, and increased area accounted for 57.79% of the total area. From 1998 to 2008, vegetation NPP showed a decreasing trend overall, and reduced area accounted for 57.94% of the total area. On the whole, in addition to a handful of region accounted for 1.76% in the West of Daxue Mountain and the northern of Laji Mountain, central and southern regions in Qilian Mountains of vegetation NPP are increased in the past 50 years.(3) From 1958 to 2008, Vegetation NPP in Qilian Mountains increased area in spring accounted for 8.85% of the total area, reduced area accounted for 5.76% of the total area; vegetation NPP in summer increased area accounted for 45.37% of the total area, reduced area accounted for 3.51% of the total area; vegetation NPP in autumn increased area accounted for 56.95% of the total area; vegetation NPP in winter accounted for 98.6% of the total area region has remained basically unchanged, reduced area accounted for 1.4% of the total area.(4) From 1958 to 2008, evergreen coniferous forest, deciduous coniferous forest, grassland, shrub and farmland NPP showed a wavy increasing trend in Qilian Mountains, but the increasing rate and the ratio are difference. From the point of NPP increase rate, the sequences is farmland > evergreen coniferous forest > deciduous coniferous forest > grassland > shrub. By the annual increase volume of NPP, the sequences is shrub > grassland > farmland > deciduous coniferous forest > evergreen coniferous forest.(5) From 2015 to 2055, the annual change of vegetation NPP in Qilian Mountains showed a wavy increasing trend. Vegetation NPP in Qilian Mountains gradually increased from the northwest to the southeast in space. In the west region, there is bare land more, and vegetation NPP is close to 0. In South-central region, vegetation types are some grassland shrub and farmland, and vegetation NPP value is about 0~260 g·m-2·a-1(C). The north central and eastern region has large areas of grassland and deciduous coniferous forest, and vegetation NPP is 260~330 g·m-2·a-1(C). To the north of tuolai Nanshan, Lenglong ridge, Wushao ridge and Laji mountain area, vegetation types are grassland, shrub, farmland, evergreen coniferous forest and deciduous coniferous forest, and vegetation NPP is 330~400 g·m-2·a-1(C). In the north and southeast of Laji mountain, more concentrated evergreen coniferous forest, NPP is about 400~601 g·m-2·a-1(C), the highest value is 601 g·m-2·a-1(C).(6) From 2015 to 2055, evergreen coniferous forest, deciduous coniferous forest, grassland, shrub and farmland NPP showed a wavy increasing trend in Qilian Mountains, but the trend is not the same. From the point of NPP increase rate, the sequences is farmland > grassland > deciduous coniferous forest > shrub > evergreen coniferous forest. By the annual average of NPP, the order is evergreen coniferous forest > farmland > deciduous coniferous forest > grassland > shrub. |
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