Vegetation Dynamics And Its Driving Force In Four Sandy Lands Of Northern China Based On Geodetector

Vegetation is an important factor connecting soil,water,air and other natural geographical environment elements.Vegetation is an important part of the ecological construction of the area,especially in desertification areas.Long term of vegetation cover is an important indicator to judge the ecological environment status.The four major sandy lands in northern China(Mu Us Sandy Land,Otindag Sandy Land,Horqin Sandy Land and Hulun Buir Sandy Land)are located in arid and semi-arid areas,which are typical ecological fragile zones.In recent years,because of the influence of climate change and human activities,regional vegetation cover changes have become more complex.It is urgent to carry out quantitative research on vegetation cover changes and the impacts of natural and human factors on vegetation covers in the four major sandy lands of northern China.Based on the MODIS NDVI data from 2000 to 2020,combined with natural data and human activities data,this paper analyzes the temporal and spatial variations of vegetation cover in the four sandy lands of northern China in the past 20 years by linear trend analysis method and Geodetector model.And the separate and coupling effects of natural factors and human activities on vegetation cover are analyzed.The main conclusions are as follows:(1)The vegetation cover of the four sandy lands in northern China is generally dominated by less vegetation and moderate vegetation,and the proportion of dense vegetation is relatively low.Among them,the NDVI in Mu Us Sandy Land was the smallest,and the NDVI in Hulun Buir Sandy Land was the largest.From 2000 to 2020,the vegetation cover of the four sandy lands in northern China showed upward trend.The increasing trends of Mu Us Sandy Land,Otindag Sandy Land,Horqin Sandy Land and Hulun Buir Sandy Land were 0.035/10a(p<0.001),0.012/10a(p<0.05),0.024/10a(p<0.001)and 0.014/10a(p<0.1),respectively.Spatially,from 2000 to 2020,the vegetation cover of the four sandy lands in northern China showed an overall increase trend,and the percentage areas of vegetation improvement in Mu Us Sandy Land,Otindag Sandy Land,Horqin Sandy Land and Hulun Buir Sandy Land accounted for 99.31%,85.97%,89.31% and 85.79% of each sandy area,respectively.(2)Among the natural factors,annual precipitation was the main limiting factor of vegetation cover in Mu Us Sandy Land,Otindag Sandy Land and Hulun Buir Sandy Land,with explanatory power of 13.6%,68.7% and 64.7%,respectively.Relative humidity was the main driver of vegetation cover in the Horqin Sandy Land,with an explanatory force of19.5%.Among the human activities,livestock density at the end of the year was the main driving factor affecting vegetation cover in the Mu Us Sandy Land,with an explanatory force of 11.8%.The cumulative afforestation area density was the main driving factor affecting the Otindag Sandy Land and the Horqin Sandy Land,with explanatory forces of64.2% and 21.6%,respectively.The effects of population density,livestock density at the end of the year and cumulative afforestation area density on Hulun Buir Sandy Land were similar,with explanatory powers of 31.9%,31.8% and 31.4%,respectively.(3)The interaction between the two driving factors of the four sandy lands in northern China was mainly based on double synergy and nonlinear synergy.Specifically,the Mu Us Sandy Land was mainly showed by the double synergistic interaction between precipitation and relative humidity,and the explanatory power was 22%.the double synergistic interaction between precipitation and cumulative afforestation area density was showed in the Otindag Sandy Land,and the explanatory power was 71%.The Horqin Sandy Land was mainly showed by the double synergistic interaction between relative humidity and the density of cumulative afforestation area,and the explanatory power was 34%.Hulun Buir Sandy Land was mainly based on the double synergistic interaction of precipitation and average temperature,and the explanatory power was 72%.(4)With the increase of annual precipitation,the mean NDVI values of the four major sandy lands in northern China showed an increasing trend,and the suitable distribution ranges of annual precipitation in Mu Us Sandy Land,Otindag Sandy Land,Horqin Sandy Land and Hulun Buir Sandy Land were 447～492 mm,429～472 mm,453～504 mm and399～429 mm,respectively.With the increase of cumulative afforestation area,the NDVI of the four major sandy lands in northern China showed a fluctuating trend,and the suitable distribution ranges of the cumulative afforestation area density of Mu Us Sandy Land,Otindag Sandy Land,Horqin Sandy Land and Hulun Buir Sandy Land were 23.1～27.6hectares/ km~2,29.2～57.7 hectares/ km~2,24～26.1 hectares/ km~2 and 1.96～2.56 hectares/km~2,respectively.This paper systematically studies the vegetation cover changes by MODIS NDVI data.And the quantitative attributions of natural factors and human activities on vegetation cover of four major sandy lands in northern China were analyzed based on the Geodetector model.The research results can provide a certain scientific basis for the prevention and control of desertification,ecological environment construction and regional sustainable development of northern China.