Spatial-tempora Variation Of Vegetation Cover And Its Driving Forces In Farming-pastoral Ecotone Of China

As the main body of terrestrial ecosystem,vegetation is not only the bearer of climate change,but also has a positive feedback effect on climate change.Its degree of change can be used as an important indicator to measure the ecological trend of a region and plays a "indicator" role in the study of global change.The farming-pastoral ecotone of China is a highly sensitive region of global climate change,and it is also a region with intensive human activities.It is the intersection of agricultural civilization and nomadic civilization.In this paper,based on GIMMS NDVI3 g data,climate data and DEM data,the temporal and spatial characteristics of vegetation cover and its response to climate change and human activities in the farming-pastoral ecotone of China from 1982 to 2015 were studied by using trend analysis,coefficient of variation,partial correlation analysis and residual analysis.The study revealed the impact mechanism of climate change and human activities on vegetation cover change,provided guidance for the development of farming-pastoral ecotone of China,and provided scientific basis for ecological environment protection.The main results are as follows:(1)Spatial and temporal changes of vegetation cover: In terms of time variation,vegetation cover in the farming-pastoral ecotone of China increased significantly from 1982 to 2015,with an increase rate of 0.72%/10a;In terms of spatial distribution,the vegetation coverage in the study area showed a spatial pattern of “high on both sides,low in the middle,high in the south,and low in the north”.NDVI first decreased with elevation and then increased significantly,then falls again.The change of the number of pixels was opposite.The average value of NDVI was the smallest in the area of 1200-1800 m,but the area was the largest.In terms of change trend,the area coverage of vegetation increased and decreased accounted for 70.56% and 29.44% respectively in the farming-pastoral ecotone of China during 1982-2015.In vertical distribution,the trend of NDVI increased first and then decreased with the increase of altitude,and the trend was the largest in the area of 1800-2400 m.In terms of stability,the stability of vegetation cover change in the study area was mainly low fluctuation change,followed by medium fluctuation change,and the proportion of high fluctuation change area was the smallest(5.88%).(2)Response of vegetation cover change to climate:In terms of climate change,the annual average temperature in China's farming-pastoral ecotones showed a significant upward trend,with a growth rate of 0.334 °C/10 a,while precipitation showed a downward trend with a drop rate of 18.139 mm/10 a.In space,the area with rising temperature accounted for 96.91%,and the area with decreasing precipitation accounted for 75.14%.In terms of the relationship between vegetation cover and climate change,temperature was the main factor affecting vegetation change in the study area compared to precipitation.(3)Contribution of climate change and human activities to vegetation cover change: In terms of interannual variation,the residual value corresponding to human activities showed a significant upward trend with a growth rate of 0.5%/10 a during 1982-2015.In space,the positive and negative residual trends respectively account for 64.06% and 35.94%.In terms of comprehensive impacts,the impacts of human activities on vegetation change were greater than those of climate change on vegetation change.