Evaluation Of Ecological Effect Of Returning Farmland To Forest In Yan 'an City Based On Difference Attribution Method

Vegetation,as the main body of terrestrial ecosystem,is called "green reservoir" and plays an important role in ecological service function.With the rapid development of economy,ecosystem degradation has become one of the serious problems facing the whole world.China has become one of the key countries in the world in ecological governance.As a typical ecologically fragile area in China,the loess plateau has suffered large-scale destruction and loss of vegetation for a long time due to human activities such as blind deforestation and overgrazing.With the deterioration of the ecological environment,China gradually realized the urgency of ecological construction and began to carry out a series of ecological restoration projects.Since the ecological policy of returning farmland to forest was implemented in Yan'an City,ecological environment and vegetation have been improved to some extent.Therefore,the research on the evaluation of the effects of ecological policies is of great significance for scientifically formulating ecological policies and improving the pertinence,scientificity,and efficiency of ecological engineering implementation.Based on this,this study uses vegetation index and land use data,the spatial and temporal characteristics of land cover change and vegetation restoration before and after returning farmland to forest in Yan'an City were analyzed by using GIS spatial platform;Using geographical detector to detect the contribution of each factor and the interaction between the two factors to vegetation restoration.On this basis,meteorological,topographical and socio-economic factors are taken as control variables,the spatial differences and reasons of the contribution of ecological policies to the effects of vegetation restoration from 1999 to 2015 were explored by using the geographical weighted regression model,the main conclusions are as follows:(1)From 1999 to 2015,the cultivated land decreased significantly,while the forest land increased significantly,forest and grassland coverage increased by 10.9 percent.In time,compared with 1999-2010,the rate of conversion from 2010 to 2015 decreased,while the intensity of forest land and grassland increased.Spatially,the intensity of returning farmland to the north of Yan'an City was relatively high from 1999 to 2010.Spatially,from 1999 to 2010,the northern area of Yan'an City had a high intensity of conversion,the southern area is mainly for forest and grassland conservation,from 2010 to 2015,forest and grassland conservation was distributed in most areas of Yan'an City.(2)Since the implementation of the project of returning farmland to forests,under the combined influence of natural and human factors,from 2000 to 2015,vegetation in Yan'an City increased significantly,and the overall vegetation coverage improved.The result of the factor detector showed that the vegetation restoration in counties and districts of Yan'an City was different.(3)Most of the interactions among the factors are non-linear.Among them,the interaction between natural factors and natural factors,natural factors and social factors such as human activities,and the interaction between social factors and social factors are non-linear.Interactions with each other increase the explanatory power of local vegetation enhancement.The vegetation enhancement in Yan'an is the result of the comprehensive influence of natural and human factors,human factors are superimposed on natural factors,which together affect the growth and protection of vegetation in Yan'an area.(4)The results of the general regression analysis show that the explanatory variables that reflect the ecological policy,such as the intensity of returning sloping land to forest(grass),forest land conservation and grassland conservation,all have a positive effect on vegetation restoration,normalized regression coefficients are 0.229?0.212 and 0.006 respectively.It shows that the ecological policies of returning farmland,prohibiting logging and grazing have been actively implemented,which effectively promotes the vegetation restoration in the study area.(5)The results of GWR analysis also show that ecological policies have promoted the restoration of local vegetation.The improvement of vegetation index is the result of the combined effects of ecological conversion,forest conservation and grassland protection under the condition of resource endowment.The geographic weighted regression establishes a model in each part,and can calculate the contribution degree(regression coefficient)of each local and different variables.It provides tool support for policy-making according to local conditions and efficient promotion of ecological environment.