Spatiotemporal Evolution Of Vegetation Cover And Its Driving Forces In Southwest China

Vegetation,as the main body of terrestrial natural ecosystem in China,is not only the bearer of climate change,but also has a positive feedback effect on climate change.As an important indicator of a country or region's ecological environment health,its change degree plays an important"indicator"role in the study of global ecological change.Based on MODIS NDVI,SRTM DEM,precipitation,temperature,humidity and sunshine duration data,Combined with methods such as Theil-sen trend analysis,Mann-Kendall significance test,multiple regression analysis,residual analysis,relative effect analysis,and Pearson correlation analysis,the temporal and spatial evolution characteristics of vegetation cover in Southwest China from 2001 to 2019 were studied.The characteristics of vegetation cover change under the influence of climate change and human activities in Southwest China were quantitatively analyzed to explore the correlation between vegetation NDVI and various meteorological factors.The results are as follows:(1)From 2001 to 2019,the NDVI of vegetation in the karst area of Southwest China showed a significant increasing trend(R~2=0.908,P<0.01),with an increasing rate of 0.025/10a.In terms of spatial distribution,the vegetation coverage of different geomorphic units in the southwest karst region has certain differences from 2001 to 2019,which generally presents a spatial pattern of"higher in the south,lower in the north,higher in the east,and lower in the west".In terms of spatial characteristics,the trend from west to east is upward,and from southeast to northwest is downward.In terms of stability,the NDVI of vegetation in the study area tended to be basically stable.The low and low fluctuation areas accounted for 92.49%of the study area,while the high and high fluctuation areas only accounted for 1.34%,concentrated in the Hengduan Mountain area,and the rest were scattered in other provinces and cities.(2)In the past 19 years,the vegetation coverage in the karst area of Southwest China has improved significantly.The average relative effect of human activities on the improved vegetation cover area and the degraded vegetation cover area is 55.13%and 54.57%respectively in the karst area of Southwest China.The impact of human activities on both improved and degraded vegetation cover areas was stronger than that of climate change.It is concluded that human activities are the key driving force affecting the vegetation growth in the karst area of Southwest China,and they have dual effects.The relative effects of climate change and human activities on vegetation cover improvement zones and vegetation cover degradation zones show obvious spatial heterogeneity.(3)In the relationship between NDVI of vegetation and related factors of climate change in karst areas of southwest China from 2001 to 2019,NDVI of vegetation was positively correlated with precipitation,air temperature and relative humidity in this region.On the whole,the mean value of the maximum correlation coefficient from high to low was the precipitation>temperature>humidity,while NDVI of vegetation was negatively correlated with sunshine duration.Among the time lag effects of vegetation NDVI on climate change,the response of vegetation NDVI to precipitation and temperature changes has a strong time lag,while the response of vegetation NDVI to humidity and sunshine duration changes has a low time lag.