| Vegetation is an important part of the Earth's ecosystem,and it is responsible for protecting the natural environment while providing essential resources for human activities.As a typical area of ecological environment construction and sustainable development,the Loess Plateau has received extensive attention from scholars at home and abroad.Vegetation has a huge impact on soil erosion in this area,and it is also a relatively intuitive factor that can reflect changes in human activities such as climate change and social economy.Therefore,it is of great significance to study the driving force of vegetation cover change.This study used satellite remote sensing images(including Landsat TM\MSS,MODIS NDVI,GIMMS NDVI)to analyze the northwestern region between Hekou Town and Longmen in the Loess Plateau with the worst vegetation and the most serious soil erosion in the historical period.The extent and process of vegetation cover change in the past 35 years,and the main driving force of vegetation change during this period was analyzed,and the following main conclusions were obtained:1.From the time scale,from 1981 to 2017,the vegetation coverage in the study area showed an overall growth trend.The vegetation cover change was not obvious from 1981 to1985.The vegetation cover appeared slowly improved from 1986 to 2005.After 2006,the vegetation entered a rapid improvement period.Before 1981,the coverage rate of forest and grass in the study area was mostly less than 20%;in 2016,the coverage rate of forest and grass in most areas was 40-60%.2.On the spatial scale,the coverage of forest and grass in most of the research areas is currently 40 to 60%,but in the northwest part where rainfall and soil conditions are poor,and the area of ??the sloping land is relatively large.The area is still less than 40%.It reflects that natural factors and human activities can have a decisive influence on forest and grass coverage.3.Rainfall and human activities are the key factors affecting the change of vegetation cover,but the contribution rate of the two factors in different periods is very different.The relationship between rainfall in the vegetation growth period(August to September)and the NDVI response at different stages from 1981 to 2016 was analyzed.It was found that before2005,the correlation between rainfall and NDVI was not obvious,indicating the rainfall tovegetation.The growth-promoting effect is basically offset by the destruction of vegetation by humans.Human activities such as expansion,overgrazing and felling are the decisive factors for the development and growth of vegetation in the area.In the rapid improvement of vegetation from 2006 to 2016,there was a significant positive correlation between rainfall and NDVI(correlation coefficient R2 was 0.77).The more rainfall and the greater the degree of vegetation coverage,the less human damage to vegetation during this period.Rainfall is a key factor affecting vegetation cover.In fact,in 2006-2011,when the rainfall was obviously dry,the vegetation in the area still showed a rapid improvement.4.The reduction of human destruction of vegetation activities since 2006 is related to the rapid development of the local economy and the massive reduction of agricultural population.Taking Shenmu County in the study area as a typical area,select GDP,GDP per capita,raw coal output,per capita net income of farmers,agricultural population,cultivated land area,annual rainfall and temperature,etc.,using principal component analysis,2000-2016 The change of vegetation cover and the response relationship of various factors were analyzed.The results showed that the GDP,per capita GDP,per capita net income of farmers,raw coal production and agricultural population represented the local economic level,indicating the economic development level and agricultural population.The quantity has a great impact on the change of vegetation cover in the county.The more developed the economy and the less the agricultural population,the better the vegetation improvement.In addition,the recent increase in rainfall and temperature increase have also had a positive impact on vegetation restoration.On the whole,since 2000,the significant reduction of human disturbance to the land has been the main driving force for the improvement of vegetation cover in Shenmu County.5.The field survey conducted in 9 villages of Shenmu County in the study area shows that in the past ten years,the proportion of actual rural population in rural areas has been11%,and the number has shown a sharp decline.Urban development has attracted a large amount of rural labor,most of which the cultivated land has been abandoned,and the number of cattle and sheep has been greatly reduced.These factors have greatly reduced the disturbance to the land,which is conducive to the restoration of vegetation. |
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