| Global warming is a major challenge facing mankind at present,which requires the joint efforts of the international community to address.And China has set a clear strategic goal of carbon peaking and carbon neutrality,to achieve which reducing carbon emission and increasing carbon sequestration are two major breakthroughs.However,blindly reducing emissions will inevitably hurt economic growth.And thus,in the process of achieving the carbon peaking and carbon neutrality goals,the role of enhancing carbon sequestration is particularly important.The Sixth Assessment Report(AR6)of the Intergovernmental Panel on Climate Change(IPCC)shows that vegetation carbon stocks account for 31%of carbon sequestration in terrestrial ecosystems,which in turn account for about 50%of global carbon stocks.Therefore,enhancing the carbon sequestration capacity and efficiency of forests and grasslands plays a decisive role in increasing carbon sequestration,and ecological carbon fixation of terrestrial vegetation has great potential in the process of achieving the goal of carbon peaking and carbon neutrality in China.Since 1990s,the Chinese government has successively implemented a series of ecological restoration policies,which not only greatly promoted the restoration and reconstruction of degraded ecosystems,significantly improved the ecological environment,but also objectively promoted the enhancement of vegetation carbon sequestration.Among them,Grain for Green policy,implemented since 1999,has the largest implementation scope and the most profound impact on terrestrial ecosystem.Due to the long-time span of Grain for Green project,which makes it difficult to obtain the vegetation and carbon sequestration data before afforestation,some scholars introduced space-for-time substitution method to select reference samples whose habitat were similar to the current evaluated object.But there is no guarantee that these selected reference objects and evaluated object shared a same state at the beginning.And in fact,for the certain objective criteria(e.g.,slope condition)during site selection for Grain for Green,the sample selection does not meet the random assumption.Selection deviation will lead to the theoretical assumption failure of traditional evaluation methods.Therefore,based on the traditional space-for-time substitution method,a local window space-time differential model,which can effectively eliminate the impact of heterogeneity factors(e.g.,time,space and habitat conditions)in the measurement of carbon sequestration enhancement effect brought by Grain for Green policy,was developed,making the measurement results more scientific and reasonable.On the basis of improving the measurement model,this study also analyzed the spatial differentiation pattern and influencing factors of carbon sequestration enhancement effect brought by Grain for Green policy.Firstly,with GIS platform,the carbon sequestration enhancement effect of Grain for Green policy was visualized,and its spatial distribution characteristics were analyzed.Furthermore,Geodetector and Multiple linear regression were introduced to analyze the influencing factors affecting the carbon sequestration enhancement effect of Grain for Green policy quantitatively.In this study,these influencing factors were selected from three aspects:natural environment,social-economic conditions and ecological policies itself.And then,the influence degree,influence direction and interaction mechanism of each environmental factor on the carbon sequestration enhancement effect brought by Grain for Green policy were obtained based on empirical analysis.This study can provide decisionmaking reference for project layout and policy optimization.The main conclusions of this study are as follows:(1)The change of net primary productivity(NPP)of terrestrial vegetation in Loess Plateau was clarified,and the total carbon sequestration enhancement effect of terrestrial vegetation from 2000 to 2020 was obtained.On the temporal trend,the NPP in Loess Plateau increased year by year from 2000 to 2020.Over 98%of the terrestrial vegetation showed a positive increase in carbon sequestration.The average total increase in carbon sequestration reached 1388.7 kg/ha,which means the carbon sequestration enhancement effect of regional vegetation was significant.On the spatial distribution,the NPP in Loess Plateau keeps the spatial differentiation law of high in the southeast and low in the northwest,and the total enhancement in carbon sequestration from 2000 to 2020 also shows the same spatial distribution characteristics,which depends on the superior resource endowment conditions and relatively strong policy implementation in the southeast of the Loess Plateau.(2)A local window space-time differential model was developed to effectively separate the carbon sequestration enhancement effect of Grain for Green policy,based on which the spatial differentiation characteristics of Grain for Green policy’s carbon sequestration enhancement effect was also analyzed.The results show that the average carbon sequestration enhancement effect of Grain for Green policy is 50kg/ha in Loess Plateau,which means the implementation of ecological policy has a certain positive effect on the vegetation carbon sequestration enhancement.At the same time,on the spatial differentiation pattern,the carbon sequestration enhancement effect of Grain for Green policy also showed a spatial distribution pattern of high in the southeast and low in the northwest.The low is concentrated in Qinghai,Gansu,Ningxia and Inner Mongolia,but the high is concentrated in Shaanxi,Shanxi and Gansu Province,among which the carbon sequestration enhancement effect of Grain for Green policy in Shaanxi Province is most remarkable.It is suggested that ecological policy can play a greater role in enhancing vegetation sequestration in areas with superior resource endowment.(3)Through factor detection and multiple linear regression,the key factors affecting the carbon sequestration enhancement effect of Grain for Green policy in Loess Plateau were analyzed.The results show that potential achievement representing the vegetation restoration effect of ecological policies is the key factor and its influence on the carbon sequestration enhancement effect of Grain for Green policy in Loess Plateau is greater than the factors such as multi-year average precipitation,multi-year average temperature and soil particle content.Thus,the implementation effect of ecological policies plays a leading role in vegetation carbon sequestration enhancement of ecological policies.(4)Based on interactive detection,the influence of environmental factors on the carbon sequestration enhancement effect of Grain for Green policy in Loess Plateau was analyzed.It is found that the interaction of various environmental factors had a nonlinear enhancement effect on the carbon sequestration enhancement effect of Grain for Green policy,especially the interaction between potential achievement and natural factors;But its interaction with socio-economic factors was also significant.In the implementation process of ecological policy,attention must be paid to coordinate ecological policy with natural environment and social-economic conditions,not only better to maintain and implement ecological policies but further to promote the enhancement of vegetation sequestration.(5)Through multiple linear regression,the influencing direction of environmental factors on the carbon sequestration enhancement effect of Grain for Green policy was analyzed.The results show that in greater potential achievement areas with sunny aspect,rich soil particles,high temperature,little rainfall,sparse population and dense roads,the unit area of Grain for Green can often bring more vegetation sequestration enhancement.Therefore,it is necessary to optimize the policy design according to local conditions to promote the early realization of the carbon peaking and carbon neutrality goals. |
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