| Fractional Vegetation Cover(FVC)is an important indicator parameter that reflects the growth and distribution of land surface vegetation and regional environmental quality.It plays an important role in evaluating the structure and function of regional ecosystem.The role of subtropical vegetation in the global ecosystem carbon cycle and maintaining the carbon balance of the system has attracted more and more attention.The subtropical region of China has complex,diverse,and widely distributed vegetation that grows year-round,and it is China's main agricultural and forestry production base.At the same time,there are also prominent problems in the region,such as poor forest quality and low forest productivity and yield rates.Moreover,subtropical forest vegetation and its ecological functions are very sensitive to global climate change.Therefore,monitoring the temporal and spatial evolution characteristics of FVC in the subtropical region,clarifying the response of FVC to climate change,and exploring the impact mechanism of FVC on Net Primary Productivity(NPP)under the background of climate change,which will have important reference significance for the sustainable management of vegetation,the improvement of productivity,as well as the environmental protection and rational allocation of resources in the subtropical region.In this study,the vegetation in the subtropical region of China was taken as the research object,and remote sensing data such as MODIS land surface reflectance(MOD09A1)from 2001 to 2018 were used as data sources,the FVC in the subtropical region was obtained by using the dimidiate pixel model and analyze its spatial and temporal evolution characteristics.Then,combined with the meteorological data of the same period,used the partial correlation analysis and the partial derivative model to analyze the influence of climate factors on FVC.Finally,based on the MODIS land cover type,Leaf Area Index(LAI),meteorological data etc.,the BEPS model was driven to simulate the NPP of vegetation in the subtropical region from 2001 to 2018,and analyzed the impact of subtropical FVC on the spatiotemporal evolution of NPP under the background of climate change.Through research,the following three conclusions are obtained:1.In terms of the characteristics of the temporal and spatial dynamics variation of FVC in the subtropical region.(1)From 2001 to 2018,FVC in the subtropical region of China showed a significant growth trend,the interannual variations and fluctuations were relatively small overall,basically maintaining a relatively stable state.(2)From the spatial distribution pattern of FVC,the level of vegetation coverage in the eastern subtropical region was higher than that in the western region as a whole.And FVC in more than 70% of the subtropical region was high-coverage and medium-coverage,among them,the proportions of the area with an increasing trend and a decreasing trend in FVC are 76.28% and 23.72% in the past 20 years,respectively.2.In terms of the response of FVC in the subtropical region to climate factors.(1)The results of the partial correlation analysis showed that the area where the average annual minimum temperature and the annual precipitation had a positive impact on the increase of subtropical FVC accounted for 62.06% and55.26% of the study area respectively,while 58.12% of the subtropical region showed that the average annual maximum temperature had a negative effect on FVC.(2)The contribution analysis results based on the partial derivative model showed that the average annual minimum temperature was the main climate contribution factor to the dynamic variations of China's subtropical FVC.In addition,the main climate influencing factors of FVC variation in various regions were different,and the FVC variation in some regions was also affected by the joint influence of multiple climate factors.3.In terms of the temporal and spatial evolution of subtropical vegetation NPP and its response to FVC under the background of climate change.(1)In the past 20 years,the spatial distribution of NPP of subtropical vegetation generally showed a pattern of "high in the south and low in the north,and high in the east and low in the west".(2)In terms of time,the annual average value of subtropical vegetation NPP showed an overall increasing trend over time,and the fluctuations were relatively stable.(3)The average annual minimum temperature was the main climate contribution factor to the dynamic variations of vegetation NPP in the subtropical region.Among them,53.05% and 71.17% of the subtropical region showed that the average annual maximum temperature and the annual precipitation had a positive impact on vegetation NPP,while 56.20% of the region showed that the average annual minimum temperature had a negative impact on vegetation NPP.(4)The average correlation coefficient between vegetation NPP and FVC in the subtropical region was 0.04,and the spatial distribution difference of their correlation was "positive south and negative north,positive east and negative west".And FVC in medium-coverage zone and high-coverage zone had a strongest correlation with vegetation NPP. |
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