Evaluation And Optimization Of The Ecological Effects Of Returning Grazing To Grassland Based On The Realization Of The Potential Of Vegetation Restoration

The Tibet Autonomous Region is my country’s largest production base of grassland animal husbandry and an important ecological barrier,with grassland area accounting for20.5% of the country.Severely restricted by the natural environment and social conditions,grassland resources are the material basis for the survival and economic development of local people.Since the beginning of this century,with the deterioration of grassland ecology,the state has initiated the ecological project of returning grazing to grassland in natural grassland.At the same time,with regard to “degraded,desertified,and salinized” grasslands,policy tools such as fences and prohibition on grazing have been adopted to promote the implementation of the ecological project of returning grazing to grassland to take effect.。The academic community pays close attention to the implementation effects and influencing factors of the ecological project of returning grazing to grassland,and has carried out a series of evaluation studies with a view to optimizing the layout of future ecological project construction.This article focuses on Gaize County,the second largest pure animal husbandry county in the Tibet Autonomous Region.Taking the fence construction in 2013 as the time node,the study period 2008-2018 is divided into two phases: 2008-2013 and2013-2018,and introduced Vegetation restoration "potential-realization" model and time-space double difference evaluation method to evaluate the implementation effect of the restoration of grazing to grass ecological project,and use multiple linear regression and GWR model to explore how to realize the greatest possible vegetation restoration potential and affect grazing restoration The factors of returning grass to the ecological effect provide policy suggestions for improving the grassland ecology.The main conclusions are as follows:(1)Use MODIS data to extract and calculate the change trend of the Enhanced Vegetation Index(EVI)in Gaize County from 2008 to 2018.The results show that the change trend of EVI in Gize County from 2008 to 2013 was relatively flat,the growth rate was slow,and the inter-annual change rate was 0.00004/a;the EVI of Gize County from2013 to 2018 showed a trend of substantial growth,with the inter-annual change rate It is0.00169/a.On the whole,under the background of the implementation of the Ecological Project of Returning Grazing to Grassland,the growth of vegetation in Gaize County has improved significantly.(2)Under the ArcGIS platform,combined with the classification results of the natural breakpoint method,the calculated slope layers of EVI changes at different periods of time are divided into 6 different types of vegetation restoration levels,and these 6 different vegetation restoration levels are counted.Type of area.The results show that the total degraded area from 2008 to 2013 accounted for 46.95%,which shows that grassland degradation is very serious.After the continuous implementation of the grazing-returning-grass project,the overall vegetation coverage in Gaize County was improved from 2013 to 2018,and the total degraded area fell to 20.02%,which was 26.93%less than before implementation.(3)Introduce the "potential-realization" model of vegetation restoration to measure the effect of vegetation restoration in Gaize County since 2008.The results show that the change trend of the realization degree of vegetation restoration potential in Gize County from 2008 to 2013 was negative.From 2013 to 2018,the change trend of the realization degree of vegetation restoration potential in Gaize County was positive,and the change trend of realization degree of vegetation restoration potential changed from negative to positive,which also indicates that the implementation of the grazing restoration project has shown obvious results.(4)Expanded the time and space double difference evaluation method.The time difference results show that only 2 fences have a negative growth in their vegetation restoration potential,and the remaining 15 locations have a positive growth in their vegetation restoration potential.It can be seen that the overall vegetation restoration effect in the study area has been better since the fenced grazing prohibition.However,this is not necessarily the effect of the fenced grazing prohibition policy,which includes the contribution of factors other than the fenced grazing prohibition project.The results of the double difference of time and space further show that the realization of the vegetation potential of 58.82% of the fenced area grows faster or degenerates more slowly than the adjacent area,which can be regarded as a pure fenced grazing prohibition project effect.(5)Using multiple linear regression models to analyze the influencing factors of vegetation restoration effects.From the overall construction of the model,the goodness of fit(R2)of the model is 0.203,and the F test is significant at the 0.05 level of significance.From the specific regression coefficients of variables,the regression coefficient of population density is 0.018,which is significant at the 0.05 level of significance.It shows that through the implementation of the grazing restoration project,the greater the population density,the more obvious the effect of vegetation restoration.However,the regression coefficients of the two explanatory variables of the village collective annual economic income and the number of village groups are not significant,indicating that they have limited effects on the vegetation restoration of the grazing restoration project.(6)Use the Geographically Weighted Regression(GWR)model to explore the magnitude,direction and significance level of the influence of the respective variables in different regions on the dependent variable,and summarize their spatial distribution rules.The results show that population density has a greater impact on the difference in the realization of vegetation restoration potential before and after the implementation of grazing and grass restoration,and the change in population density has a more obvious effect on the improvement of vegetation restoration in the northern part of the study area.The collective income of the villages in the western part of Gaize County has a greater negative impact on the difference in the realization of vegetation restoration potential before and after the implementation of grazing restoration.(7)Adopt two methods of bivariate correlation analysis and bivariate spatial autocorrelation analysis to respectively explore the influencing factors and spatial correlation of the vegetation restoration effect of the fenced grazing prohibition project.The results of bivariate correlation analysis show that the number of village groups has a positive and significant impact on the difference in potential realization,which confirms that the management and maintenance of fences has a great impact on vegetation restoration.The results of bivariate spatial autocorrelation analysis show that population density is one of the important reasons for the difference in vegetation restoration inside and outside the fence.In areas with high population density,the effect of vegetation restoration through the implementation of fenced grazing prohibition in the surrounding areas is better.