Study On Dynamic Changes And Driving Factors Of Vegetation In The Southwest China During 2001-2016

The change of surface vegetation can reflect the natural conditions and the changes of human activities in some regions.It can provide a scientific basis for formulating a reasonable land use mode and carrying out effective ecological environmental protection.The five provinces of the Southwest,Sichuan Province,Chongqing City,Yunan Province,Guizhou Province and Guangxi Zhuang Autonomous Region were taken as the Study area.The time series of MODIS NDVI data sets from 2001 to 2016,DEM data,meteorological data,land use data were used in this study.The special tools,incluing ArcGIS,ENVI and C Programming language,were used in our data pre-processing and analysis.The analysis methods included trend analysis,spatial statistics and correlation analysis.Firstly,we analyzed the temporal and spatial dynamic characteristics of vegetation coverage in the past 16 years,which included time variation characteristics,spatial distribution,and spatial variation trend.Southwest China is the most widely distributed kaster areas,which is also the largest contiguous exposed area of carbonatite in the world.So the vegetation changes of spatial and temporal characteristics were studied in the past 16 years for the karst areas in Southwest China.Finally,the natural and man-made factors on the vegetation cover changes were analyzed by using correlation analysis methods.The correlation relationships between vegetation SINDVI and meteorological factors were comprehensively analyzed at the annual scale.Combined with statistical data,the impact of human activities on vegetation change in Southwest China was analyzed from land use,ecological construction and urbanization effect.The main conclusions of the paper are as follows:(1)In the past 16 years,the SINDVI in the Southwest China shows an increasing trend of fluctuation and the linear increasing rate is 0.752/10 a.SINDVI is relatively high and the average SINDVI is 12.12 in the Southwest China.The SINDVI values increased firstly and then decreased with the increase of elevation and slope.The broad-leaved forest has the maximum average SINDVI value and it is 14.69.Conversely,the shrub forest has the minimum average SINDVI value and it is 9.11.(2)The SINDVI in the southwest China has been generally improved in the past 16 years.The areas with significantly increasing trends account for 39.28% and the areas with significantly decreasing trends account for 2.54%.Therefore the increasing areas are much more than the decreasing areas.With the increase of altitude and slope,the improved and degraded trends are both decreased.The improved trend of the agroforestry is the most obvious,and the degraded trend of the coniferous forest is the most obvious.(3)In the past 16 years,SINDVI in karst regions has shown a fluctuation with totally increasing trend and the linearly increased rate is 0.836/10 a.The vegetation coverages from high to low are Guangxi Zhuang Autonomous Region,Yunnan Province and Guizhou province.Compared with 2001-2008 years,SINDVI increased by 0.58 in 2009-2016 years.There is the largest increasing trend of the vegetation coverage in the Guizhou Province,followed by Guangxi Zhuang Autonomous Region and Yunnan province.In the past 16 years,the SINDVI in karst region has been generally improved and the areas with increasing trends account for 40.1% and the areas with decreasing trends account for 2.22%.So the increasing areas are much more than the decreasing areas.Compared with the period from 2001 to 2008,the vegetation coverages have the increasing trend and the increased range is about 5.67%.Furthermore,the increased trend in Guizhou Province is largest in the early stage.But there are obviously decreased trend in the latter stage.On the contrary,the vegetation coverages appear decreasing trend in the first stage and then the biggest increasing trend in the latter stage in the Guangxi Zhuang Autonomous Region.(4)The temperature and precipitation increased at 0.26 ?/10 a and 16.31 mm/10 a respectively from 2001 to 2016 in Southwest China.The correlation coefficient between SINDVI and precipitation is 0.185 and the correlation coefficient between SINDVI and temperature is 0.539.The areas with significantly positive correlation between SINDVI and precipitation accounted for 6.81%,and the areas with significantly negative correlation accounted for 3.74%.The areas with significantly significantly positive correlation between SINDVI and temperature accounted for 14.28% and the areas with significantly negative correlation accounted for 3.18%.Therefore,the temperature had more significant influence on the vegetation changes in Southwest China.(5)The land use,ecological construction and urbanization have a profound influence on the vegetation changes in Southwest China.In the past 15 years,the area of cultivated land,woodland,grassland,bare land and water area are generally decreasing,and the area of construction land and wetland are generally increasing.Land use presents the transformation of cultivated land to woodland and construction land.The implementation of ecological construction has played a positive role in improving vegetation coverages,which has played a significant positive effect on the regional ecological environment.The efficiency of urbanization has played a significant negative effect on the ecological environment.