Analysis On The Variation Characteristics And Driving Forces Of Vegeation Cover In The Loess Plateau

Vegetation is the main part of terrestrial ecosystem,and its change depends on the natural environment and human activities to a great extent.At present,the rise of global temperature,the rapid increase of population and economy,and the continuous development of ecological restoration projects all interfere with the process of vegetation growth and developmentleading to the complex and diverse changes of vegetation cover.The Loess Plateau is animportant ecological strategic region in China.It is of great biological and ecological significance to monitor vegetation cover change and evaluate the response mechanism and action principle of vegetation to human activities and natural factors.However,previous studies on the quantitative contribution rates of regional scale changes and inter-annual driving forces are somewhat inadequate,and the mechanism of spatial differentiation of vegetation cover is often neglected.Therefore,this study based on Vegetation Index(NDVI,Normalized Difference Vegetation Index),land cover and meteorological data,and usingsimple linear regression analysis method,the variation coefficient method to analysis NDVI variantion characteristics under the different ecological environment of the loess plateau partition and land use types from 2000 to 2017.And on this basis,the use of geographic detector and the method of multiple linear regression and the residual,The spatial differentiation mechanism of NDVI in the Loess Plateau and the relative contribution rates of climate change and human activities to interannual NDVI were quantitatively analyzed,and the main conclusions were as follows:(1)The annual variation of NDVI in the Loess Plateau has a significant periodicity.The mean value of NDVI is the highest in July and August,and the vegetation coverage is basically saturated in the whole area.The monthly variation pattern of NDVI in earth-rock mountainous region,valley plain region,loess hilly region and agricultural irrigation region is consistent with that of the study area,and the NDVI in earth-rock mountainous region and valley plain region has the highest mean value.(2)During 2000?2017,the vegetation cover of the Loess Plateau was improved on the whole,and the fluctuation was mainly low(0.08<CV?0.18).The area with extremely significant improvement(?_slop>0,P<0.01)accounted for 53.90%of the total area.Different ecological environment zones and land use types showed a trend of improvement during the study period.Under different terrain,the effect of returning farmland to forest at a slope of 10?25°was significant,and the NDVI of vegetation in low-altitude agricultural areas and high-altitude forest areas was significantly improved.(3)Natural factors were the main factors affecting the spatial distribution of vegetation cover in the Loess Plateau,and human activities played a supplementary role.Among them,precipitation,relative humidity,sunshine duration and vegetation types had the greatest influence on NDVI,with explanatory power greater than 45%.When precipitation is 417.60?742.54mm,relative humidity is 71.59?86.91%,sunshine duration is 835.79?1106.16 h,temperature is 6.24?14.07?,slope is 15?25°and>25°,geomorphic type is large undulation mountain,vegetation type is broad-leaved forest,soil type is eluvian soil,land use type is woodland,afforestation quantity is 0?27.09 km²,vegetation growth is suitable.The interaction between each factor had a greater impact on NDVI than that of a single factor,and the interaction between meteorological factors and human activities was the most significant.(4)The key factor for the improvement of NDVI on the Loess Plateau is human activities,with a relative contribution rate of 80.05%and climate change rate of 19.95%.In the areas where NDVI actually improved,the relative contribution rate of climate change to the increase of NDVI was21.99%,and the contribution rate of human activities was 78.01%.In the actual NDVI degradation area,the decrease of NDVI was mainly affected by human activities(77.10%),and the contribution rate of climate change was22.90%.Human activities are the dominant factor in NDVI improvement or degradation of ecological environment zones and land use types.In Henan Province,climate change is the dominant reason for NDVI degradation,while in other provinces(autonomous regions),human activities are the main reason for NDVI change...