| The Loess Plateau has been concerned as an ecologically sensitive region over a long period of time.Under the background of climate change and the implementation of Grain to Green project,studying the change of vegetation cover and its drivers in the Loess Plateau is crucial for the sustainable development and ecological construction in the Loess Plateau.Based on the MODIS data(MOD44B,MOD17A3),meteorological data(temperature and precipitation)and socio-economic data(population,gross domestic product)of Loess Plateau during 2000-2014,the study is aimed to: 1)reveal spatial and temporal variation of vegetation cover in the Loess Plateau from 2000 to 2014;2)analyze the effects of climatic factors on vegetation cover in Loess Plateau;3)explore the effects of social factors on vegetation cover in Loess Plateau using the structural equation modeling.Results showed that:(1)Vegetation cover fluctuated significantly from 2000 to 2014 in the Loess Plateau,increasing with an insignificant rising trend.The tree cover increased significantly(r=0.864,P<0.01),40.56% of the total area of Loess Plateau experiencing an extremely significant increase,mainly distributes in north Shaanxi and Lvliang Mountain area.Tree cover with an insignificant increasing trend accounted for 41.675 % of the Loess Plateau.Tree cover was significantly higher in rainy area than in arid area,with little difference in non-tree cover.The increase of tree cover was accompanied by the decrease of non-tree cover in rainy area,this might be caused by the implementation of Grain to Green project.(2)Temperature and precipitation are considered as the most important two climatic factors to vegetation cover.Temperature had an insignificant trend from 2000 to 2014 in the Loess Plateau,64.28% of the total area of Loess Plateau showing an insignificant negative correlations with tree cover.The area with a significant increase of precipitation accounted for 5.11%,mainly distributes in north Shaanxi and Xinzhou Shanxi.The area with an insignificant increase of precipitation accounted for 76.72%.Precipitation was positively correlated with tree cover,15.12 % and 59.64% of the Loess Plateau showed significant and insignificant correlation respectively.Precipitation significantly increased vegetation cover,tree cover and NPP in different climatic zones in Loess Plateau.NPP was much more sensitive to precipitation under cold and drought circumstances.Precipitation and temperature can not only affect NPP directly,but also affect NPP indirectly by vegetation cover.Tree cover imposed higher influence on NPP than non-tree vegetation cover did.Climatic factors had a stronger indirect effect on NPP in rainy area compared with arid area.Overall,precipitation is an important climatic factor limiting the growth of vegetation in the Loess Plateau.(3)There are a larger population and a higher population density in the area of tree cover with insignificant increase.More burdens on the environment exert a negative effect on the restoration of vegetation;There is lower population density in the area of tree cover with significant increase.With the intensification of urbanization,rural population migrates to urban,causing decrease in rural population and human activity,benefiting the restoration of vegetation at these areas to some extent.With the economic growth,it has been found that the economic development has a significant negative impact on the restoration of tree cover in the area of tree cover with significant increase,such phenomenon was not found in the area of tree cover with insignificant increase.This may be related to the increasing demand of water caused by the increase of industrial and agricultural activities along the Yellow River.Water supply has become the limiting factor for the growth of vegetation and economic in the Loess Plateau,water shortage has become a key problem for the sustainable development of the Loess Plateau. |
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