Study On The Change Of Vegetation Coverage And Its Driving Factors In The Upper Reaches Of Ganjiang River Basin

Global climate change and terrestrial ecosystem response are the core research content of the International Geosphere Biosphere Project(IGBP),and terrestrial ecosystems are the life systems for human survival and development.Vegetation is the main body of the terrestrial ecosystem and has ecological functions such as maintaining water and soil,improving soil,regulating climate,and purifying air.Vegetation connects the soil circle,atmosphere,and hydrosphere,and plays an important role in the material circulation and energy flow of each circle.Therefore,studying vegetation changes is of great significance for evaluating regional environmental quality and maintaining regional ecosystem balance.The disorderly mining of rare earths in the upper reaches of the Ganjiang River basin has caused ecological and environmental problems such as vegetation destruction,soil pollution and water pollution.Vegetation can effectively inhibit soil erosion and improve the ecological environment of the region,and the fractional vegetation coverage can objectively reflect the overall condition of the regional ecological environment.Therefore,based on MODIS NDVI data,meteorological data,DEM data,and social statistical data,this paper uses trend analysis,coefficient of variation,Hurst index,correlation analysis,and residual analysis to study the change of vegetation coverage and its driving factors in the upper reaches of Ganjiang River basin from 2000 to 2018.The main conclusions are as follows:(1)In terms of time,the fractional vegetation coverage in the upper reaches of the Ganjiang River basin showed a significant upward trend(P<0.05),with a growth rate of5.31%/10 a.The fractional vegetation coverage in the four seasons showed an overall upward trend,and the growth rate was summer(4.1%/10a)>winter(3.98%/10a)>autumn(3.44%/10a)>spring(2.75%/10a).In terms of space,the vegetation coverage in the upper reaches of the Ganjiang River basin was relatively good,with higher and high vegetation coverage mainly,showing the distribution characteristics of low in the middle and high on all sides.The vegetation coverage changes in the study area were mainly stable,and the areas with stable vegetation coverage accounted for 75.96%,which were mainly distributed in mountainous areas with higher altitudes.Areas with extremely unstable vegetation coverage accounted for 1.02%,mainly distributed in the middle of Xinfeng County,the middle and east of Nankang District,the middle of Yudu County,the south of Xingguo County,and the middle of Ruijin City.The vegetation change in the upper reaches of the Ganjiang River basin was dominated by weak anti-sustainability,and the fractional vegetation coverage will show a slight downward trend in the future.(2)The average partial correlation coefficient between fractional vegetation coverage and temperature in the upper reaches of the Ganjiang River basin was:summer>autumn>winter>spring.The average partial correlation coefficient between fractional vegetation coverage and precipitation in the upper reaches of Ganjiang River basin was: summer(0.067890)>winter(0.067778)>autumn>spring.Fractional vegetation coverage was positively correlated with precipitation and temperature in summer,autumn and winter,but fractional vegetation coverage was negatively correlated with precipitation and temperature in spring.The annual fractional vegetation coverage in the upper reaches of the Ganjiang River basin had a higher correlation with temperature.The high-value areas of coefficients of multi-correlation were mainly located in the northern part of Gan County,the southern part of Xingguo County,the central part of Yudu County,the central part of Huichang County,the northern part of Anyuan County,and the northern part of Quannan County.The low-value areas of the coefficient of multi-correlation were mainly located in Zhanggong District,the central part of Gan County,the western part of Chongyi County,and the western part of Shangyou County.With the increase of elevation,the fractional vegetation coverage first increased,then remaind unchanged and then decreased.The average fractional vegetation coverage on steep slopes was the highest,and the fractional vegetation coverage on flat land was the lowest.The fractional vegetation coverage on the northern aspect was the highest,and the fractional vegetation coverage on the flat land was the lowest.There was little difference in fractional vegetation coverage in each aspect,and the aspect had little effect on the fractional vegetation coverage.(3)The increase in afforestation area promoted the increase of FVC,but FVC had a time lag on the afforestation area.The afforestation area increased before FVC,and then FVC increased.The fractional vegetation coverage in the upper reaches of the Ganjiang River basin decreased with the increase of population density.The fractional vegetation coverage in the upper reaches of the Ganjiang River basin decreased with the increase of GDP.The minimum average residual value of fractional vegetation coverage in 2002 was-0.048294,and the maximum average residual value of fractional vegetation coverage in2012 was 0.042864.From 2000 to 2018,the proportion of the area where fractional vegetation coverage increased in the upper reaches of the Ganjiang River basin was affected by climate change was 24.58%,and the percentage of the area where fractional vegetation coverage decreased affected by climate change was 45.42%,the percentage of the area where fractional vegetation coverage increased affected by human activities was24.93%,the percentage of the area where fractional vegetation coverage decreased affected by human activities was 5.07%.The contribution rate of climate change to the change of fractional vegetation coverage in the upper reaches of Ganjiang River basin was 70.00%,and the contribution rate of human activities to the change of fractional vegetation coverage in the upper reaches of Ganjiang River basin was 30.00%.