Influence Of Topography And Climate On Temporal And Spatial Variation Of Vegetation Cover In Shaanxi Province

The ecological restoration with increased vegetation coverage improved soil erosion and stability of the ecosystem,since the implementation of the Grain for Green project in Shaanxi Province.Vegetation coverage,as a crucial component of the ecosystem,is greatly influenced by topographic and climatic factors.To analyze the spatial and temporal characteristics of vegetation coverage variation and its response to climatic and topographic factors,to explore the main drivers of vegetation coverage variation,and to measure the potential for vegetation restoration in Shaanxi Province is important to promote the sustainable development of ecological construction.We calculated fractional vegetation cover（FVC）from 2000 to 2018in Shaanxi Province based on MODIS NDVI data.Analyzed the spatial and temporal variation characteristics of vegetation coverage with leaf area index（LAI）data at annual,seasonal and monthly scales.Analyzed the spatial distribution characteristics of vegetation coverage change types by Sen+Mann-Kendall method.Determined the response of vegetation coverage to topographic and climatic factors by the topographic area difference correction factor and the correlation coefficient method.We probed the main drivers and interactors of vegetation coverage variation by geodetector,and explored the sustainability of vegetation coverage variation by Hurst index,and measured the vegetation restoration potential.The main results of this study are as follows:（1）Spatially,vegetation coverage increased gradually from north to south in Shaanxi Province.From 2000 to 2018,the growth rates of FVC and LAI were 0.0026 yr^-1 and 0.0524yr^-1 respectively.The vegetation coverage in Shaanxi Province is mainly improved,with the worst coverage but most significant improvement in the northern Loess plateau,a slight increase in vegetation cover in the Qinling-bashan mountain,and a slight decrease in vegetation cover in the Guanzhong plain.Temporally,from 2000 to 2018,vegetation coverage in Shaanxi Province increased significantly,but the growth trend gradually slowed down.There were significant seasonal differences in vegetation coverage variation,with the highest FVC growth rate in spring(0.0069 yr^-1)and the highest LAI growth rate in autumn(0.0518yr^-1).（2）The variation of vegetation coverage was significantly positively correlated with climate factors at monthly and seasonal scales,while it was not significant at the annual scale.The time-lag duration between vegetation coverage and climate factors is dominated by 1-3months,except for the conjunctional areas of Guanzhong plain with the Loess plateau and Qinling-bashan mountain,which exhibits 5-6 months.Topographically,the landform of hills had the highest FVC increment at the altitude of 500-1500 m,the slope of 2°-6°.The dominant driving factors on vegetation coverage variation in Shaanxi Province were climate factors.However,the main drivers vary within the three topographic zones.In the Loess plateau,they were precipitation,temperature and sunshine duration.Dominant factors in the Qinling-bashan mountain were topographic relief,whereas in the Guanzhong plain,they were relief and sunshine duration.Multiple factors interacting together better than a single factor to explain the dynamics of vegetation coverage variation.（3）The variation of vegetation coverage in Shaanxi Province is stable,with the continuing improved area proportions of FVC and LAI at 11.70%and 18.20%respectively.The spatial variability of the province’s vegetation restoration potential is evident,with areas of high potential concentrated in the northwestern part of the Loess Plateau and conjunctional areas of Guanzhong plain with the Loess plateau.As a dense urban area,the Guanzhong Plain is predominantly degraded;Ziwuling forest area in the south of Loess Plateau and Qinling-bashan mountain,with less space for vegetation restoration and stable development.（4）As important vegetation indices,both FVC and LAI have their own strengths in reflecting different vegetation information.FVC is more suitable for studies of vegetation degradation and vegetation response to climate change;FVC restoration potential is more influenced by vegetation type.Compared with FVC,LAI showed more significant seasonal variability.LAI is more suitable for studies of vegetation improvement and vegetation response to topographic features.LAI restoration potential is more influenced by sunshine duration.