Spatiao-temporal Evolution Of Vegetation And Its Response To Climate Change And Human Activities In Shandong Province

Vegetation,as an important component of ecosystems,controls the exchange of carbon,water,energy and momentum between the land and the atmosphere,and plays an irreplaceable role in maintaining climate stability and advancing climate intervention policies.It is significant to examine the spatial and temporal dynamics of vegetation cover and its driving factors in Shandong Province under the climate change context for the sustainable development of the regional ecological environment,rational planning of territorial spatial patterns and achieving the strategic goal of carbon peaking and carbon neutrality.Therefore,this study focused on Shandong Province and selected the normalized difference vegetation index（NDVI）and leaf area index（LAI）to characterize the vegetation cover.Based on the189 actual meteorological station data,MODIS type product data from 2001 to 2020 and land use data,this study employed ANUSPLIN interpolation,Mann-Kendall significance test and Theil-Sen Median trend analysis,time-series stability analysis,multi-order partial correlation analysis,multiple regression residual analysis and partial differentiation principle,clarified the spatial and temporal distribution of vegetation cover and climate in Shandong Province from 2001 to 2020,revealed the influence of the climate features on the change of vegetation cover,and assessed the contribution of human activities and climate change to the change of vegetation cover.The primary conclusions were as follows:（1）The intra-annual variation of vegetation cover in Shandong Province from 2001 to2020 showed the typical single-peaked curve.On average,the average annual change rates of NDVI and LAI in Shandong Province during the study period were 7×10^-5yr^-1（p>0.05）and3.1×10^-2yr^-1（p<0.01）,respectively,with the largest average annual increase rates of NDVI and LAI in Dezhou at 2.3×10^-4yr^-1（p<0.05）and 0.06 yr^-1（p<0.01）,respectively,and the largest average annual decrease rates of NDVI and LAI in Weihai at-2.5×10^-4yr^-1（p<0.01）and-0.01 yr^-1（p>0.05）,respectively.Spatially,the trends of both NDVI and LAI in Shandong Province were dominated by the non-significant increase.The results of time-series stability analysis showed that NDVI changes in Shandong Province were extremely stable in the past 20 years,whereas LAI changes were fluctuated,and the future vegetation cover changes in Shandong Province were dominantly increasing to decreasing.（2）The intra-annual variation of precipitation and temperature in Shandong Province from 2001 to 2020 showed the single-peaked curve,and that of relative humidity and wind speed showed the single-period cosine waveform and single-period sinusoidal waveform,respectively.During the study period,the inter-annual variations of precipitation and relative humidity showed the significant decreasing trend,with the non-significant decreasing trend in the inter-annual variation of relative humidity,the significant increasing trend in the inter-annual variation of temperature,and the significant decreasing trend in the inter-annual variation of wind speed,their annual average change rates were-0.1 mm yr^-1（p>0.05）,-0.1%yr^-1（p>0.05）,0.05℃yr^-1（p<0.01）and-0.04 m s^-1yr^-1（p<0.01）,respectively.The temperature in all cities and regions is on an upward trend,the relative humidity is on a downward trend,the wind speed is on a downward trend,and the precipitation trend has some regional differences.During the study period,the area of land use conversion in Shandong Province was about 1.79×10⁴km²,accounting for about 11.7%of the total area of the province,and the types of land use change were mainly arable land conversion out and impervious surface conversion in.（3）Vegetation cover in Shandong Province from 2001 to 2020 was positively correlated with precipitation,negatively correlated with temperature and wind speed.During the study period,changes in precipitation,temperature and relative humidity drove the decrease in NDVI and changes in wind speed dominated the increase in NDVI;changes in precipitation and temperature resulted in the decrease in LAI,whereas relative humidity and wind speed led to the increase in LAI.Climate change was the dominant driver for vegetation cover change in Shandong Province from 2001 to 2020,with its regional average contributions of67.2%and 69.3%to changes in NDVI and LAI,respectively.In general,the vegetation cover change in Shandong Province in the last 20 years dominated by climate-driven vegetation cover increase,and although human activities was the key factor leading to the vegetation browning in Shandong Province during the study period,it was still undeniably drove the vegetation cover tendency to increase in 7.5%of Shandong Province.