【作者】 张玉；

【导师】 张道军； 龚直文；

【作者基本信息】 西北农林科技大学 ， 农林经济管理， 2023， 硕士

【摘要】 全球气候变暖是当前人类面临的重大挑战,应对全球变暖需要国际社会共同努力,我国已制定了明确的碳达峰和碳中和时间表。减少碳排放和增加碳汇是实现双碳目标的两大突破口,而一味减少排放必然会对经济增长产生负面影响。因此,在实施双碳目标的过程中,增加碳汇的作用就显得尤为重要。国际政府间气候变化专门委员会(IPCC)的第六次评估报告(AR6)显示,陆地生态系统固碳量约占全球碳储量的31%,其中植被碳储量又占陆地生态系统固碳量的50%。因此,增强林业和草原碳汇能力和效率,对增加碳汇量具有举足轻重的作用,陆地植被生态固碳在我国实现双碳目标进程中大有可为。20纪90年代以来,中国政府先后实施了一系列生态恢复政策,不仅对退化生态系统的恢复与重建起到了巨大的推动作用,显著改善了生态环境,也在客观上发挥了一定的增汇效应。其中自1999年开始实施的退耕还林政策实施范围最大,对陆地生态系统的影响也最为深刻。由于退耕还林工程实施时间跨度大,造林前的植被和碳汇数据获取较为困难,一些学者引入了空间代替时间法,选择与当前待评价对象生境相似的地块作为参照样本。然而,并不能保证待评价地块与参照样本在起初具有同样的状态。事实上,因为退耕还林工程实施区域的选址需要满足一定的客观标准,例如坡度条件,样本选择并不满足随机假设,选择偏差也会导致传统评价方法的理论假设失效。为此,本研究在传统空间代替时间方法基础上,发展了局部窗口时空双重差分模型,该模型可有效消除退耕还林政策增汇效果测度中时间、空间以及生境条件等异质性因素的影响,测度结果更加科学合理。在改进生态政策的陆地植被增汇效果测度模型基础之上,本研究还分析了退耕还林政策增汇效果的空间分异格局和影响因素。首先,借助GIS平台对退耕还林政策增汇效果进行可视化制图,并分析退耕还林政策增汇效果的空间分布特征。进而,引入地理探测器和多元线性回归实现对影响退耕还林政策增汇效果环境因素的定量分析。本研究分别从自然环境、社会经济状况以及生态政策实施3个层面选取影响因子,基于实证分析获取各环境因子对退耕还林政策增汇效果的影响程度、影响方向和交互机制,从而为工程布局和政策优化提供决策参考。本研究得出的主要结论如下:(1)阐明了黄土高原陆地植被净初级生产力的变化情况,获取2000-2020年陆地植被总增汇效果。时间趋势上,2000-2020年黄土高原陆地植被净初级生产力逐年上升,98%以上地区的陆地植被表现出正向增汇作用,黄土高原平均总增汇量达到了1388.7kg/ha,区域植被增汇效果显著;空间分布上,黄土高原陆地植被净初级生产力始终保持东南高西北低的空间分异规律,2000-2020年区域陆地植被总增汇也具有同样的空间分布特征,这依赖于黄土高原东南部优越的资源禀赋条件以及较大的政策实施力度。(2)发展了局部窗口时空双重差分模型,实现退耕还林政策增汇效果的有效分离,并对其空间分异特征进行了剖析。结果显示,黄土高原平均退耕还林政策增汇效果为50kg/ha,生态政策的实施对黄土高原植被固碳量的增加具有一定的积极作用;同时,在空间分异格局上,黄土高原退耕还林政策增汇效果同样呈现东南高西北低的空间分布格局。退耕还林政策增汇低值集中在青海、甘肃、宁夏以及内蒙古境内;而高值则集中在陕西省、山西省以及甘肃省境内,以陕西省退耕还林政策增汇效果最为明显。提示在资源禀赋优越的地区,生态政策能够发挥更大的植被增汇作用。(3)通过因子探测和多元线性回归分析了影响黄土高原退耕还林政策增汇效果的关键因子。因子探测和多元线性回归结果均表明代表生态政策植被恢复成效的潜力实现度指标是影响黄土高原退耕还林政策增汇效果的关键因子。其对黄土高原退耕还林政策增汇效果的影响程度要大于多年平均降水、多年平均气温、土壤颗粒含量等因素。可见,生态政策实施成效对生态政策增汇效果具有主导作用。(4)基于交互探测分析了各环境因子两两交互对黄土高原退耕还林政策增汇效果的影响。研究发现,各种环境因子的交互作用对退耕还林政策增汇效果产生了非线性增强的影响,尤其是潜力实现度与自然因素之间的交互作用;但其与社会经济因素的交互作用同样比较显著。在生态政策实施过程中,必须注重政策与自然环境和社会经济条件的协同,才能更好地维护和落实生态政策,进一步促进当地植被增汇效果的提升。(5)借助多元线性回归分析了各种环境因子作用于退耕还林政策增汇效果的方向。在阳坡、土壤颗粒含量丰富、高温少雨、人口稀疏和道路密集的潜力实现度越大的区域,单位退耕还林还草面积往往能够带来更大的植被增汇量。因此,必须因地制宜优化政策设计,促进“双碳”目标早日实现。更多还原

【Abstract】 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.更多还原