Spatial And Temporal Changes Of Vegetation Coverage Response To SLCP In The Middle And Upper Reaches Of The Yellow River

The SLCP is the largest ecological program with largest investment in China.The implementation of the program is not only related to the ecological restoration within the two major river basins and ecologically fragile areas,but also has an effect on the production and living style of local residents,even the industrial structure and economic development mode,which makes a great significance to evaluate the effect of this program.The vegetation coverage is influenced directly by the SLCP and is also a result of natural conditions and human activities.Because of the stability of natural conditions,the ecological effects of the program could be reflected by the spatial and temporal changes of vegetation coverage.Nevertheless,it should be noted that the evolution of vegetation coverage is the product of the comprehensive effect of natural and socio-economic factors.Therefore,in order to avoid deviation of research results,we should not confine ourselves to the consideration of policy factors,when analyzing the driving mechanism of vegetation coverage.This paper firstly summarized the research progress of the SLCP in China and other countries by using the method of literature review.And then,based on 144 counties in the middle and upper reaches of the Yellow River as the research objectives,the paper qualitatively described their natural conditions,social and economic conditions and implementation progress of the SLCP,which laid a foundation for the analysis of the research results.In order to represent the growth status of vegetation coverage,this paper used Normal Difference Vegetation Index(NDVI)to preliminarily analyze the characteristics about the response of vegetation coverage to the SLCP in the study area by means of mean method and trend analysis method.Considering the possible influence of the spatial lag,this paper used global Moran' I to determine whether the value of NDVI was spatial dependent,and used Getis-Ord index G to study the spatial concentration of vegetation coverage and to analyze the characteristics about the response of vegetation coverage to the SLCP further.Finally,the paper established a theoretical model between vegetation coverage and its driving forces by using spatial panel regression.And based on the analysis of direct and indirect effects in the model results,the effects of the SLCP on vegetation cover were analyzed.The results showed that:(1)the vegetation coverage gradually decreased from southeast to northwest in the middle and upper reaches of the Yellow River;(2)because of the implementation of the SLCP,the vegetation coverage had improved.But there was a coexistence of ecological restoration and ecological deterioration;(3)there were hot spots and cold spots of vegetation coverage in the study area and the boundary was around the line of the 400 mm amount of precipitation;At the same time,the area of hot spots was smaller than that of cold spots because of the restriction of natural conditions.The areas with the high response level to the SLCP are North Shaanxi,Loess Plateau in Central Shaanxi,Southwest and Southern Gansu.And the areas with the low response level to the SLCP are Northern and central Ningxia,Central Gansu and Guanzhong Plain in Shaanxi;(4)Precipitation was a restrictive factor for vegetation in arid and semi-arid regions,and high precipitation had a direct impact on vegetation growth which positively affected the vegetation coverage in the region and adjacent areas at the same time;(5)The positive impact of population quality on vegetation coverage in one specific county was more significant than that in the surrounding area;(6)The spatial and temporal changes of vegetation coverage has a high response to the SLCP.The implementation of the project had the most direct effect on vegetation restoration,which made the vegetation coverage improve significantly in a short time,and the improvement of vegetation status in one specific county would have a positive effect on vegetation coverage in the surrounding areas.This conclusion provided the theoretical support for the establishment of ecological linkage mechanism among different counties,and promoted the cooperation and exchange of ecological restoration,so as to improve the implementation effect of the SLCP.