Responses of vegetation cover to the Grain for Green Program and their driving forces in the He-Long region of the middle reaches of the Yellow River

The implementation of the Grain for Green Program is a great breakthrough in the history of China＇s ecological environment construction,which can control soil erosion effectively,increase land productivity and improve the ecological environment.To investigate the eco-environmental benefits brought by the Grain for Green Program,the spatiotemporal variations of vegetation cover in the growing season from 2000 to 2010 across the Hekou-Longmen （He-Long） region were analyzed by using remote sensing information,meteorological data and land use data.Moreover,the impacts of climate and human activities on vegetation change were evaluated objectively.Annual vegetation cover in the growing season increased very significantly.Increased vegetation cover occurred in 98.7％ of the region,of which the area for vegetation cover improved slightly constituted 79.8％ of the whole area.Vegetation moderately improved was mainly distributed in the south of the He-Long region,covering 9.6％ of the area,and the area for vegetation basically unchanged concentrated in the middle and upper reaches of the Wuding River.Precipitation was found to be an important natural factor influencing vegetation cover change.The area of vegetation cover showing a significantly positive correlation with precipitation occupied 22.14％ of the region.As driven by policies from the Grain for Green Program,forestland increased significantly and land use structure became more intensive.Human activities played a positive and effective role in the protection,restoration and improvement of vegetation in the places where vegetation cover was basically unchanged,even though precipitation declined greatly,and vegetation improved moderately with massive increases of forestland and grassland.

Changes in Land Use and Agricultural Production Structure Before and After the Implementation of Grain for Green Program in Western China–Taking Two Typical Counties as Examples

Soil erosion becomes a serious environmental problem in the world, especially in western China. An effective management practice called the Grain for Green Program(GGP), which was launched in 1999, aims to reduce soil and water loss and alleviate the ecological environment problem in western China. Two typical counties in western China, the Zhongxian(in Chongqing Municipality) and Ansai(in Shaanxi Province) were chosen to evaluate the dynamic changes of land use and agricultural production structure before and after the implementation of the Program in this paper. The results showed that the cultivated land area was reduced by 7.08% from 1989 to 2003. The cultivated land per person was decreased by 8.42% during 1999-2003. Moreover, the stability index of the secondary sector of the economy was increased from 0.91 in the period 1990-1999 to 0.94 in the following ten years. In addition, the stability index of tertiary economic sector increased from 0.88 to 0.92 in Zhongxian county. Meanwhile, the cultivated land area was reduced by 15.48% from 1990 to 1999. The soil erosion modulus was decreased by 33.33% from 1999 to 2006. Also, the stability index of secondary and tertiary economic sectors was 0.86 in the period 1998-2002. However, it decreased by 77% during 2002 to 2007 in Ansai County. These results imply that the Grain for Green Program had different impact on the two regions. Several effective strategies of soil and water conservation have been carried out to ameliorate the sustainable development of ecological environment and economy in these two counties of western China.

Coupling between the Grain for Green Program and a household level-based agricultural eco-economic system in Ansai,Shaanxi Province of China

The implementation of the Grain for Green Program(GGP)has changed the development track of the agricultural eco-economic system in China.In response to the results of a lag study that investigated the coupling between the GGP and the agricultural eco-economic system in a loess hilly region,we used a structural equation model to analyze the survey data from 494 households in Ansai,a district of Yan’an City in Shaanxi Province of China in 2015.The model clarified the direction and intensity of the coupling between the GGP and the agricultural eco-economic system.The coupling benefits were derived through linkages between the program and various chains in the agricultural eco-economic system.The GGP,the agroecosystem of Ansai and their potential coupling effects were in a state of general coordination.The agroecosystem directly affected the coupling effect,with the standardized path coefficient of 0.87,indicating that the agroecosystem in Ansai at this stage provided basic material support for the coupling between the GGP and the agricultural eco-economic system.The direct path coefficient of agroeconomic system impacted on the coupling effect was-0.76,indicating that partial contradictions occurred between the agroeconomic system and the coupling effect.Therefore,although the current agroecosystem in Ansai should be provided sufficient agroecological resources for the benign coupling between the program and the agricultural eco-economic system,agricultural development failed to effectively transform agroecological resources into agricultural economic advantages in this region,which resulted in a relative lag in the development of the agricultural economic system.Thus,the coupling between the GGP and the agricultural eco-economic system was poor.To improve the coupling and the sustainable development of the agricultural eco-economic system in cropland retirement areas,the industrial structure needs to be diversified,the agricultural resources(including agroecological resources,agricultural economic resources and agricultural social resources)need to be rationally allocated,and the chain structure of the agricultural eco-economic system needs to be continuously improved.

Trade-offs and Synergies of Ecosystem Services in Karst Area of China Driven by Grain-for-Green Program

As an important means regulating the relationship between human and natural ecosystem,ecological restoration program plays a key role in restoring ecosystem functions.The Grain-for-Green Program(GFGP,One of the world’s most ambitious ecosystem conservation set-aside programs aims to transfer farmland on steep slopes to forestland or grassland to increase vegetation coverage)has been widely implemented from 1999 to 2015 and exerted significant influence on land use and ecosystem services(ESs).In this study,three ecological models(In VEST,RUSLE,and CASA)were used to accurately calculate the three key types of ESs,water yield(WY),soil conservation(SC),and net primary production(NPP)in Karst area of southwestern China from 1982 to 2015.The impact of GFGP on ESs and trade-offs was analyzed.It provides practical guidance in carrying out ecological regulation in Karst area of China under global climate change.Results showed that ESs and trade-offs had changed dramatically driven by GFGP.In detail,temporally,SC and NPP exhibited an increasing trend,while WY exhibited a decreasing trend.Spatially,SC basically decreased from west to east;NPP basically increased from north to south;WY basically increased from west to east;NPP and SC,SC and WY developed in the direction of trade-offs driven by the GFGP,while NPP and WY developed in the direction of synergy.Therefore,future ecosystem management and restoration policy-making should consider trade-offs of ESs so as to achieve sustainable provision of ESs.

Impacts of Drought and Human Activity on Vegetation Growth in the Grain for Green Program Region,China

The Chinese government adopted six ecological restoration programs to improve its natural environments. Although these programs have proven successful in improving local environments, some studies have questioned their performance when regions suffer from drought. Whether we should consider the effects of drought on vegetation change in assessments of the benefits of ecological restoration programs is unclear. Therefore, taking the Grain for Green Program(GGP) region as a study area, we estimated vegetation growth in the region from 2000–2010 to clarify the trends in vegetation and their driving forces. Results showed that: 1) vegetation growth increased in the GGP region during 2000–2010, with 59.4% of the area showing an increase in the Normalized Difference Vegetation Index(NDVI). This confirmed the benefits of the ecological restoration program. 2) Drought can affect the vegetation change trend, but human activity plays a significant role in altering vegetation growth, and the slight downward trend in the NDVI was not consistent with the severity of the drought. Positive human activity led to increased NDVI in 89.13% of areas. Of these, 22.52% suffered drought, but positive human activity offset the damage in part. 3) Results of this research suggest that appropriate human activity can maximize the benefits of ecological restoration programs and minimize the effects of extreme weather. We therefore recommend incorporating eco-risk assessment and scientific management mechanisms in the design and management of ecosystem restoration programs.

Decomposition dynamics and ecological stoichiometry of Quercus acutissima and Pinus densiflora litter in the Grain to Green Program Area of northern China

Litter decomposition and ecological stoichiometry of nutrient release is an important part of material cycling and energy flow in forest ecosystems.In a study of the ecological stoichiometry and nutrient release during litter decomposition in a pine–oak forest ecosystem of the Grain to Green Program(GTGP)area of northern China,a typical pine and oak species(PDS:Pinus densiflora Sieb.,QAC:Quercus acutissima Carr.)were selected in the Taiyi Mountain study area.The ecological stoichiometry characteristics of carbon(C),nitrogen(N)and phosphorus(P)and litter decomposition dynamics were studied by field sampling and quantitative analyses.The results showed the following.(1)The decomposition dynamics of both litters was slow-fast-slow.The most important climatic factor affecting the litter decomposition rate from May to October was precipitation and temperature from November to April of the following year.(2)Throughout the 300-day study,in both litters,C of the two litters was released,N first accumulated and was then released,and P exhibited a release-accumulate-release pattern.(3)C:P was significantly higher than C:N and N:P(p<0.05);the C:N of PSD litter was higher than that of QAC(p<0.05),but the N:P of QAC litter was higher than that of PSD litter(p<0.05).The C:N of both litters was very high in the study area,indicating that the nutrient release ability during litter decomposition in the two typical pine–oak forest ecosystems was relatively weak;therefore,more attention should be paid to nitrogen-fixing species and mixed forests in the GTGP area of northern China.

退耕还林(草)工程对中国北方农牧交错带生态系统健康的影响

生态系统健康是生态环境治理的目标,探究国家级生态修复项目退耕还林(草)工程对中国北方农牧交错带生态系统健康的影响,确定合理的生态环境恢复和资源管理策略,有助于加快生态环境建设、促进区域可持续发展。基于“压力-状态-响应”(PSR)模型,构建起一套包括自然、社会和经济等方面的综合指标体系,评估了2000年、2005年、2010年和2015年中国北方农牧交错带的生态系统健康水平,利用Moran′s I分析退耕还林(草)工程和区域生态系统健康的空间相关性,并从普通最小二乘法、地理加权回归模型、时间加权回归模型和时空地理加权回归模型中,选择最优回归模型,揭示退耕还林还草实施强度变化(△NDVI)对生态系统健康变化(△EHI)的影响机制。结果表明:(1)2000—2015年,中国北方农牧交错带的生态系统健康指数呈现“先下降后上升”的变化趋势,区域整体处于亚健康状态和一般健康状态,健康状况逐渐转好。(2)全局双变量Moran′s I结果显示,在2000—2010年工程的开始和发展阶段,退耕还林(草)工程对生态系统健康呈现正相关影响关系,而2010—2015年间,两者之间变为负相关关系。(3)多种回归模型相比较,GTWR模型表现最优。在2000—2010年间,退耕还林(草)工程对研究区域东北部生态系统健康变化具有显著正向影响,在2010—2015年间,该区域由正向驱动变为负向驱动;中部地区则一直保持正向驱动;西南部地区则呈现“负向驱动—正向驱动—负向驱动”的波动变化情况。

基于减沙效益和经济效益的流域退耕还林方案优化

实施退耕还林,是控制中国水土流失、改善生态环境的有效途径。如何制定最具成本-效益的退耕还林方案,以平衡生态、经济和粮食安全之间的矛盾,是保证退耕还林工程可持续发展的关键。该研究以淮河上游的息县流域为研究区,在土地利用现状的基础上,一方面通过建立分布式水文模型SWAT(soil and water assessment tool)依次模拟各子流域的退耕还林操作得到泥沙削减系数,另一方面通过GDP(gross domestic product)与土地利用现状的空间叠置分析得到各子流域进行退耕还林的GDP损失系数,据此分别构成退耕还林的减沙效益目标和经济效益目标,采用多目标遗传算法NSGA-II优化求解子流域尺度的退耕还林方案。研究结果表明:1)建立的SWAT模型对研究区径流和泥沙的模拟精度较高,Nash系数分别在0.90和0.70以上,决定系数均大于0.80,且百分比偏差均控制在-20%~20%以内,可认为SWAT模型能够用于评估退耕还林的泥沙削减效果;2)子流域泥沙削减系数范围为26.70~2675.85 t/km^(2),并表现出从上游到下游逐渐减小的趋势,说明在流域上游的河源区实施单位面积的退耕还林能够取得更好的泥沙控制效果;3)子流域GDP损失系数在空间上呈现出较大的差异性,既有子流域出现了GDP的增加也有子流域出现了GDP的减小,对比发现在行政市或县主要居民点所在的子流域进行退耕还林需要付出更大的经济代价;4)多目标优化求解得到的退耕还林方案集将人均耕地面积维持在1.04×10^(−3)~1.54×10^(−3) km^(2),明显高于粮食安全的警戒水平,同时该方案集能够在仅损失30.13%~37.67%经济产值的同时将泥沙产量削减53.54%~69.86%,并达到区域可持续发展的土壤侵蚀水平。该研究提出的基于生态减沙效益和经济效益的子流域尺度退耕还林优化方法可为流域水土保持、退耕还林工程的科学规划提供借鉴和指导。

重庆市退耕还林工程林固碳潜力估算

为估算重庆市退耕还林工程林固碳潜力,调查收集重庆市2000～2007年退耕还林工程逐年造林的树种、面积等数据资料,利用国家森林资源清查资料中该市人工林生长历史数据模拟人工林生长曲线,借助该曲线并结合经调研国内外文献所得林分树种的生物质密度、碳含量、生物量开展系数等生物物理参数,设计林分碳储量变化计算模型.结果表明,重庆市退耕还林工程林的稳定碳积累量在2010、2020、2030、2040及2050年分别为14.276～14.740、33.463～41.059、43.796～57.915、50.254～70.124和54.024～77.655 Tg（T=10^12）;退耕还林工程林未来40年内具有显著碳汇功能,其年碳汇量在未来5年左右将达到高峰,2005～2020年是退耕还林工程林年碳汇能力的强盛期.

退耕还林工程对农户生产生活影响研究

研究退耕还林工程与农户的关系对于退耕还林后续问题解决,完善工程具有重要意义。该研究在准格尔旗多年农户调查的基础上,对该旗退耕还林工程初期(2002年)和后期(2010年)农户生产生活情况进行了对比研究,主要探讨了退耕还林工程对农户家庭结构、收入水平和结构的影响,以及农户对退耕还林态度、禁牧圈养态度变化和对退耕还林工程评价,最后分析了农户返耕决策。研究结果表明:受访农户平均年龄由2002年的35.02岁上升为2010年的45.32岁,年轻农户比重明显下降;户均人口从2002年的3.75人下降到2010年的2.8人。农户人均毛收入由2002年的1 332.03元增长为2010年的5 447.77元;收入结构也由牧业为主转为外出务工为主;养羊农户比重明显减小,但户均规模有增大的趋势。农户依然高度支持退耕还林,但对退耕补贴的满意度下降,大部分依然赞成禁牧和圈养,但支持力度有不同程度的下降。农户将退耕地返耕可能性较小,且大部分受访农户还支持进一步退耕。

基于参与性调查的农户对退耕政策及生态环境的认知与响应

采用参与性农户评估方法(PRA)对黄土丘陵区107户农户进行了分层随机抽样调查,并根据研究区内地形等条件将所调查农户分为旱地农户和川水地农户两组,就目前农户对退耕还林还草政策的态度及农户对生态环境的意识及行为的异同进行分析比较。尝试从农户行为角度研究区域发展问题,并基于对农户行为的分析,对区域相关政策制定、实施以及生态环境建设等提出相关建议。研究表明:研究区农户对于土地依赖性较大,旱地农户表现尤为突出,大多数农户对于退耕持支持态度。农户进行的相关水土保护措施,很大程度上并不是农户经过决策后有意识的自觉行为,而是农户为了保证基本农业生产,采取的相应的对策所产生的效应。在土地管理及水土保护措施方面,除了相关的种植措施外,旱地农户更多倾向于通过工程措施来获取好的回报,而川水地农户更多注重于现有土地质量的管护,来进一步提高现有耕地的质量。农户对于环境重要性的认识较为明确,川水地农户认识要比旱地农户更充分一些。与10a前相比,近80%的农户认为当地的生态环境有所好转,然而近45%的农户在生产活动过程中根本不考虑对生态环境的影响,两组农户之间差异不大。超过55%的农户认为生态环境恶化首要原因是气候的影响,干旱是关键因子,其次是过度放牧(24.5%)和水土流失(22.5%)等,两组农户对于生态环境恶化原因的认识具有较大的差别,旱地农户认为生态环境的恶化主要原因是干旱和水土流失,而川水地农户认为生态环境的恶化主要原因是干旱和过度放牧。

西南地区退耕还林工程主要林分50年碳汇潜力

为评估西南地区退耕还林工程主要林分未来50a碳汇潜力,调查收集该地区2011年以前退耕还林工程主要造林树种及其造林面积等相关数据资料,利用国家森林资源清查资料中人工林历史数据建立生长模型,结合文献调研获得的相关林分碳计量参数,预测出本区域退耕还林工程7种主要林分碳储量和年碳储量未来变化。结果表明:西南地区退耕还林工程主要林分总碳储量在2020、2030、2040、2050和2060年分别为52.98、73.88—80.57、73.62—102.16、88.41—115.17和77.15—123.36TgC,年总碳储量则分别为3.15、-1.11—2.45、-3.92—1.95、2.08—0.96和0.25—0.73TgC,到2060年华山松、马尾松、柳杉、杉木、柏树、杨树和桉树7种林分碳汇潜力在无采伐情景下分别达到:13.01、15.01、13.44、24.13、28.05、15.63和14.09TgC,可对本地区森林碳汇功能产生明显影响。

基于参与性调查的退耕还林政策可持续性评价——卧龙自然保护区研究

农户是退耕还林工程中的经济主体,他们的经济行为和认知响应将会对工程实施产生重要影响。研究采用参与式农户评估方法,就农户对退耕还林工程的态度和认知、退耕还林工程对农户的经济影响、以及农户现有耕地面积等问题进行了调查,以期从农户角度出发,探讨卧龙自然保护区退耕还林工程的可持续性问题。研究表明,尽管农户对退耕还林工程持积极的态度,但是有3个问题影响了退耕还林工程的可持续性。一是当地居民的粮食需求问题,由于当地居民粮食消费的外在依赖性,以及工程本身导致的耕地和收入减少,使退耕还林工程的可持续性受到潜在的威胁;二是从经济发展的角度出发,结合当地居民的经济收入、就业状况和他们对于工程的经济预期,现行的退耕还林工程缺乏相应的配套措施和足够的吸引力来保证其可持续性;三从生态恢复理论和实践上看,退耕补偿的数量和期限须考虑区域的差异和生态系统功能的实现,在本研究区域须与生物多样性保护相结合。

黄土高原典型区植被恢复及其对生态系统服务的影响

植被恢复是全球陆地生态系统恢复的主要途径,我国的大规模植被恢复具有特色,产生了巨大效益和广泛影响。退耕还林(草)是我国重大植被恢复工程的典型代表,在黄土高原地区试验示范进而推广到全国。工程实施以来,工程区植被的恢复情况及其产生的影响已成为学术界关注的热点。选取陕西省延安市、榆林市和山西省吕梁市、临汾市作为黄土高原典型区,分析了土地利用变化情况。基于2000—2014年的年均植被覆盖度数据分析了植被恢复的时空变化趋势。在此基础上,以土壤侵蚀率、地表植被蒸散(ET)和植被净初级生产力(NPP)为指标,对典型区土壤保持服务、水文调节服务和植被碳固定服务的变化进行定量评估,以此分析植被恢复对主要生态系统服务的作用。结果显示:(1)工程实施以来林地和草地范围明显增加。(2)植被改善趋势明显,2000—2005、2000—2010和2000—2014年植被显著恢复的比例分别为5.8%、49.1%和79.0%。(3)土壤保持服务增强,2014年土壤侵蚀速率比2000年降低17.5%,中度侵蚀区降幅达53.7%,2000—2014年历年土壤保持率均在84%以上且呈波动增加。(4)水文调节服务增强,2000—2010年ET增加区域面积达到48 094.1 km2,占典型区总面积的39.6%。(5)植被碳固定服务提高,2000—2014年典型区NPP总体处于增加态势,NPP显著增加区域占全区总面积的60.3%,固碳总量增加45.4%。研究表明,退耕还林(草)工程实施以来,典型区植被得到了显著恢复,有效促进了区域生态系统服务的提高,植被恢复及其生态系统服务效应的时空变异特征值得关注。

黄土高原植被恢复引发区域气温下降

黄土高原退耕还林(草)等生态恢复工程促进了地表植被覆盖增加,进而通过影响地表-大气之间热量交换影响区域气候过程。基于黄土高原1998—2000年和2008—2010年SPOT卫星反演的植被覆盖资料、54个地面气象站气温资料及EIN-Interim地表热通量数据,采用空间分析交叉验证及地表热量平衡分析的方法,从站点尺度探讨了退耕还林(草)工程初期和10年后黄土高原植被变化与气温和地表热通量变化之间的关系。研究表明,退耕还林(草)工程开展10年后,黄土高原气温最小值、最大值与平均值均有下降,植被覆盖增加与气温变量降低在空间上呈正相关。同时,植被覆盖增加与潜热通量增加、感热通量与大气下行长波辐射下降在空间上也呈正相关关系。这些结果表明,植被恢复可通过增加地表蒸散发作用对区域气候产生降温效应,会减缓气温升高对黄土高原生态系统的影响。

云南退耕还林工程林木生物质碳汇潜力

收集云南省2000—2006年各类退耕还林面积和树种数据,设定2007—2010年间的6种年度造林与采伐情景,根据云南省森林资源清查中的人工林生长数据,拟合出各造林树种的经验生长曲线,并利用这些能够反映不同气候和立地条件下人工林的平均生长曲线,结合生物量扩展因子、木材密度和碳含量等参数,估算不同情景下的林木生物质碳贮量及其变化。结果表明:云南省退耕还林工程林木生物质碳贮量在2010、2020、2030、2040和2050年将分别达到8.1～8.8、19.6～25.7、18.4～33.0、20.3～34.9和23.6～35.4TgC。退耕地造林林木生物质碳贮量占云南省退耕还林工程林木生物质碳贮量的33%～41%。

湖南会同不同退耕还林模式初期碳密度、碳贮量及其空间分布特征

对湖南会同5种退耕还林模式初期森林生态系统碳密度、碳贮量及其空间分布特征进行了研究。结果表明:主要造林树种马尾松、樟树、杜英、乐昌含笑、红花木莲不同器官的平均碳密度分别为:0.5296、0.5188、0.5178、0.5376、0.5355gC/g,树种间同一器官的平均碳密度排序为:树干>树根>树叶>树枝>树皮;5种退耕还林模式中活地被物层、死地被物层碳密度分别介于0.4380—0.5380gC/g、0.5060—0.5200gC/g之间,土壤层(0—60cm,下同)平均有机碳密度介于0.00786—0.01485gC/g之间;退耕还林3a后,乐昌含笑×红花木莲混交林、杜英×乐昌含笑混交林、杜英×樟树混交林、樟树林土壤层有机碳密度比原坡耕地分别提高了53.57%、39.19%、38.57%、24.82%,而马尾松林地下降了18.72%。林木不同器官中的碳贮量基本上与各器官的生物量成正比例,同一造林时间的4种模式中,以杜英×樟树混交林各器官的碳贮量最大,为1.219tC/hm2,杜英×乐昌含笑混交林最小,仅为0.199tC/hm2,均以干根碳贮量为最大,占其各器官碳贮量的57.50%以上。5种退耕还林模式恢复初期的生态系统中,土壤层碳贮量最大,为74.518—119.312tC/hm2,占96.180%以上,植被层为其次,在0.633—2.960tC/hm2之间,仅占0.642%—3.820%,死地被物层为最小。退耕后,樟树林、杜英×樟树混交林、乐昌含笑×红花木莲混交林、杜英×乐昌含笑混交林生态系统碳贮量分别增加了19.477、27.722、41.643、26.821tC/hm2,马尾松林下降了1.675tC/hm2。

华北低丘山地不同土地利用条件下的土壤呼吸比较

基于气体红外分析技术,在华北低丘山地退耕还林区内,以农田、撂荒地为对照,分析退耕43年和退耕10年刺槐人工林土壤呼吸速率的季节变化及其环境影响机制。结果表明:退耕43年和退耕10年刺槐人工林0～5 cm土层的土壤有机质含量分别是农田的3.9和1.6倍;退耕43年刺槐人工林、退耕10年刺槐人工林、撂荒地和农田的全年土壤呼吸平均速率分别为2.33,1.21,2.40和2.04μmol·m-2s-1,其中撂荒地的全年土壤呼吸平均速率最大,退耕43年刺槐林的全年土壤呼吸平均速率大于退耕10年刺槐林;研究区内4种土地条件下的土壤呼吸速率主要受5 cm深处土壤温度影响,退耕43年刺槐林、退耕10年刺槐林、撂荒地及农田的土壤呼吸温度敏感系数Q10分别为2.47,2.53,2.06和1.56,其中2种退耕林地的Q10均显著高于农田;4种土地利用条件下的Q10均存在显著的季节变异,其大小主要受温度影响。退耕还林工程的实施显著改善了土壤固碳能力。

退耕还林政策的有效性与有效政策搭配的存在性

论文旨在提高重启的退耕还林项目生态、经济双目标实现的有效性,具体内容如下:1理论研究。利用丁伯根和丁伯根-博弈纳什均衡理论,分别从中央政府政策制定和县级政府政策执行视角,讨论现有退耕还林政策多目标实现的有效性和退耕还林政策实施过程中与其他相关政策有效搭配的存在性。2实证检验。论文首先利用贵州省既属(国家)退耕还林项目实施区又属第二次石漠化调查区的64个县(市、区)作为样本检验退耕还林政策的有效性,用"石漠化改善率"作为项目生态目标的检验结果表明项目的生态目标实现是有效的,而用"县域2005年参与退耕还林项目的农户在2011年的人均纯收入"作为项目的经济目标进行检验的有效性未通过检验。接着,论文利用贵州省晴隆县多政策配套实施退耕还草项目的结果来检验有效政策搭配的存在性,用"植被盖度"、"土壤冲刷量"和"径流量"三个指标来反映项目的生态效果并利用观测点数据进行分析,结果表明退耕还草项目具有较显著的生态效果。用晴隆县实施退耕还草项目乡镇的农户"家庭总收入"指标反映项目经济目标,并利用农户调查数据进行实证检验,结果表明项目的经济目标实现是有效的。3研究结论。从政策设计角度看,退耕还林项目无法通过自身有效地同时实现生态、经济目标;从县级政府政策实施的角度看,若县级政府在退耕还林项目实施中能整合性地配套相关政策,则项目存在"有效政策搭配",即项目可同时有效实现生态、经济双目标。因此,在县级政府绩效考核中增加生态考核指标,进而在县级层面通过政策搭配谋求退耕还林多目标的有效实现,在生态文明建设背景下显得现实与可行。

美国自然保护计划对中国退耕还林后续政策的启示

美国的自然保护计划（Conservation Reserve Program,CRP）与我国的退耕还林工程非常相似。在比较中美两个项目的基础上,结合实地调研,分析了退耕还林工程不同的后续政策情景,提出可以借鉴CRP相应阶段的政策,同时通过严格选择退耕地块、继续提供补贴、建立信息管理系统等措施,解决退耕还林工程面临的返耕、返贫等问题,并改进退耕还林工程的费用有效性。