Spatiotemporal Variation Of Sparse Vegetation NPP In The Gurban Tungut Desert Over The Past 18 Years

Net Primary Production(NPP)is a key indicator for measuring vegetation growth and terrestrial ecosystems,which can reasonably evaluate the stability and sustainability of ecosystems.In the context of climate change,study the spatial and temporal changes and influencing factors of sparse vegetation NPP in the Gurban Tungut Desert over the past 18 years(2001-2018),reveal the driving factors and driving characteristics of NPP in the study area,to provide scientific reference for adapting to climate change and improving the fragile ecological environment of desert in arid areas.Through field investigation,combined with remote sensing inversion and mathematical statistical methods,taking the Gurban Tungut Desert as the study area and sparse vegetation as the research object,this study used the revised CASA model to built the remote sensing inversion model of the sparse vegetation NPP in the Gurban Tungut Desert,analyzed the spatiotemporal changes of sparse vegetation NPP in the Gurban Tungut Desert,clarified the relationship between meteorological factors and vegetation NPP,and discussed the mechanism and process of meteorological factors affecting vegetation NPP.The research indicates:(1)Based on the physical model inversion of LAI,FPAR parameters,vegetation canopy structure,and environmental factors(sun zenith angle,observed zenith angle,etc.),the revised CASA model simulated good NPP results.Based on the measured data(R²=0.8407,0.7903,P<0.05;RMSE=0.67,1.21)and comparison with other people's research results,the study showed that the determination of the maximum light energy utilization rate of sparse vegetation and the improved FPAR algorithm of the CASA model have a certain value for estimating the sparse vegetation NPP in the Gurban Tungut Desert,and the study fills in the missing parts of MODIS NPP products in the Gurban Tungut Desert.(2)From 2001 to 2018,the interannual change of sparse vegetation NPP in the Gurban Tungut Desert showed an overall upward trend,but the intra-year change was more obvious in the spring.Over the past 18years,the total amount of sparse vegetation NPP had fluctuated increased at an overall rate of 0.56 g C m^-2a^-1,with an average NPP of 46.90 g C m^-2 a^-1;In spring,it had increased at a rate of 0.54 g C m^-2 a^-1,and the change trend in summer and autumn was relatively stable,which was caused by different climates in different seasons.In the past 18 years,the annual average NPP had a spatial distribution pattern of low in the west-high in the east and low in the north-high in the south.However,from a dynamic perspective,it was basically stable in the desert hinterland and more active around.The NPP spatial pattern characteristics were consistent with the ways the precipitation changed with the terrain spatial distribution in the Gurban Tungut Desert.The coefficient of variation was less than 0.3 in 66.04%of the study areas,and most of areas were distributed in the hinterland of the study area with small fluctuations,the ecosystem of the Gurban Tungut Desert was in a relatively healthy and stable state,in about 70.55%of the study areas,the sparse vegetation NPP shows a trend of no significant increase and anti-sustainability in the future.In different administrative areas,the NPP increase area of each administrative area was greater than the decrease area;in the vertical direction,the increase area of sparse vegetation NPP increases-decreases with the elevation.(3)The sparse vegetation NPP in the Gurban Tungut Desert was mainly affected by precipitation,it has a positive correlation with precipitation,temperature,and elevation.The driving force analysis of each factor shows that precipitation(0.6144)>elevation(0.5812)>air temperature(0.3435)>slope(0.1413),precipitation was the dominant factor restricting the growth of sparse vegetation;spatial precipitation,temperature and sparse vegetation NPP show positive correlation areas(65.92%,75.65%)were all larger than the negative correlation areas;the relationship between sparse vegetation NPP and elevation is specifically as follows:with the increase in altitude,it decreases after a sharp increases and then slowly increases.Among the coupling effects of different factors,the combined effect of precipitation and air temperature(0.9304)had the greatest impact on NPP of sparse vegetation,followed by the synergistic effect of precipitation and elevation(0.9220).