Study On Spatial-temporal Patterns Of Net Primary Productivity Of Vegetation And Its Driving Factors In Qinghai Province

Net primary productivity?NPP?of terrestrial ecosystem,as a key parameter of terrestrial ecological process,is not only used to estimate the earth's supporting capacity and evaluate the sustainable development of terrestrial ecosystem,but also an important component and key link of global carbon cycle.As an important part of energy transfer and material cycle in terrestrial ecosystem,NPP is also one of the important research contents in global temperature change and carbon cycle.On the one hand,it reflects the productivity of plant communities in natural environment,on the other hand,it also determines the carbon cycle and accumulation of carbon and organic matter in terrestrial ecosystem.The province is a sensitive zone of climate in China and belongs to the typical plateau continental climate.The terrain of the province inclines from west to east.The complex geographical environment influences the distribution of precipitation and temperature,which results in the regional difference of vegetation.This paper is based on the 1000m resolution data set of MODIS17A3 from 2000 to 2014,and the land use data of 2000 and 2015.Based on the data of 39 meteorological stations in Qinghai Province and socio-economic data,and through the technical platforms of ArcGIS 10.0,ENVI 4.3 and Origin 9.0,using simple difference method,linear regression analysis,Hurst index and correlation analysis,the vegetation NPP of Qinghai Province in the past 15 years has been dynamically changed from five eco-functional zones,i.e.coniferous forest-alpine meadow eco-region of Qilian Mountains,II?agriculture and animal husbandry eco-region of Eastern Qinghai?,III?alpine meadow eco-region of Jiangheyuan?,IV?desert-salt crust eco-region of Qaidam Basin?and V?semi-desert-desert eco-region of northern Qiangtang Plateau?and municipal and county administrative areas.The effects of climate change,altitude and land use types on NPP change were discussed.The main conclusions were as follows:?1?The fluctuation range of the annual average NPP value in Qinghai Province from 2000 to 2014 is concentrated in 68.83-92.07 gC·m^-2·a^-1,with an average of79.05 gC·m^-2·a^-1.The minimum value in 2001 is 68.83 gC·m^-2·a^-1,and the maximum value in 2004 is 92.07 gC·m^-2·a^-1.On the whole,there are also obvious differences in NPP among different ecological regions.The trend of change is not big,basically flat.The interannual variations in other ecological regions are basically the same,showing fluctuations of decline-rise-fall-rise-fall-rise-fall-rise-fall-rise-fall.?2?From 2000 to 2014,on the whole,the distribution of annual average NPP value in Qinghai Province is basically the same as that of regional elevation.The distribution of annual NPP value is gradually decreasing from south to North and from east to west.From the point of view of ecological functional areas,the spatial difference of each ecological area is significant,which is shown as zone II>zone I>zone III>zone IV>zone V.From the perspective of administrative division,the annual average NPP of Huangnan Tibetan Autonomous Prefecture is the highest,300.27 gC·m^-2·a^-1,and that of Golmud City is the lowest,17.72 gC·m^-2·a^-1.In the southeast region suitable for vegetation growth,the NPP value is larger,but in the Northwest region,the NPP value is smaller due to the limitation of topography,precipitation and temperature.?3?Simple interpolation method,linear regression analysis and Hurst index were used to analyze the change characteristics of NPP in Qinghai vegetation from 2000 to2014.?4?The influence of climate factors?temperature and precipitation?,altitude and LUCC type on NPP in Qinghai Province is analyzed.1)The correlation with precipitation and temperature shows that the distribution of temperature correlation coefficient and rainfall correlation coefficient has a good complementarity.In areas with high temperature correlation,the correlation degree of rainfall is low,and vice versa.2)With the increase of elevation,NPP of vegetation generally showed a slow increase and then a rapid decline,a low peak,then a rapid rise,then began to decline to zero,and NPP of vegetation at different elevations showed obvious differences,with double peak characteristics.3)Land use/cover change?LUCC?research shows that in the past 15 years,the cultivated land area has been reduced least,the area has been reduced by 14 km²,the forest land area has been reduced by 76km²,the grassland area has been reduced by 1260 km²,which is the main reason for the decrease of NPP.Urban land has been increased by more than 763 km².Qinghai Province has experienced a large-scale increase.In the process of urban expansion and urbanization,some grassland and woodland are converted into construction land.