Based on the estimation of carbon cost from afforestation in project boundary and carbon leakage out of boundary in the construction period of "Grain for Green" Program (GGP) (2000-2010), the annual variance and composition of the carbon cost and carbon leakage, as well as characters of variance of net carbon sequestration were analyzed for GGP and respective program regions. Results showed that the carbon costs in northwest region, southwest region, northeast region, north region and central south and east region were 3.38, 3.64, 1.03, 1.66 and 4.38 Tg C, respectively, totaling 14.09 Tg C. Meanwhile the carbon leakages of the above regions were 21.33, 4.60, 5.50, 1.32 and 3.78 Tg C, respectively, and 36.53 Tg C in total. The composition characters of the carbon costs of the GGP and the respective regions were similar. Carbon emissions from afforestation were the largest carbon cost, and afforestation on converted farmland was the main carbon emission source. Accordingly, among the materials consumed, fertilizer brought about the largest carbon cost, followed by building materials, while carbon emissions from fuels, irrigation, herbicides and pesticides only accounted for about 10% for respective regions. The carbon cost and carbon leakage of the GGP were 50.62 Tg C in total, which counteracted 19.9% of the sequestered carbon in the program. In northwest region, southwest region, northeast region, north region and central south and east region, carbon emissions (including cost and leakage) accounted for 38.9%, 10.4%, 26.1%, 8.9% and 15.5% of the carbon sequestration, respectively. The net carbon sequestration of the GGP was 203.50 Tg C with an annual average of 18.50 Tg C·a-1. The carbon cost and leakage offset a minor part of the carbon sequestration of the GGP. Therefore, the GGP contributed significantly to greenhouse gas mitigation in China as well as global climate warming mitigation. Adopting precision fertilization in economic forest afforestation and supplying alternative livelihoods to farmers in the program could be the potential measures to reduce carbon cost and carbon leakage.
基于退耕还林工程建设期(2000—2010年)营造林过程边界内碳成本和边界外碳泄漏的计算,分析退耕还林工程及各区域碳成本和碳泄漏的年际变化、碳成本和碳泄漏的组成特征以及净固碳量的变化特征.结果表明: 退耕还林工程建设期内,西北地区、西南地区、东北地区、华北地区、中南华东地区的碳成本分别为3.38、3.64、1.03、1.66、4.38 Tg C,合计14.09 Tg C;碳泄漏分别为21.33、4.60、5.50、1.32、3.78 Tg C,合计36.53 Tg C.退耕还林工程及各区域工程措施碳成本组成特征较为一致,造林引起的碳排放是各区域最大的工程措施碳成本,其中退耕地造林是主要的造林碳成本来源.在各种物资消耗中,肥料引起的碳排放是各区域最大的物资碳成本,其次为建材,而燃油、灌溉和药剂产生的碳排放占各区域碳成本总量的比例仅为10%左右.退耕还林工程的实施在工程边界内外共产生温室气体50.62 Tg C,抵消了工程固碳效益的19.9%;在西北地区、西南地区、东北地区、华北地区和中南华东地区的抵消作用分别为38.9%、10.4%、26.1%、8.9%和15.5%.退耕还林工程建设期内的净固碳量为203.50 Tg C,年均净固碳量为18.50 Tg C·a-1.碳成本和碳泄漏对退耕还林工程固碳的抵消较小,退耕还林工程在我国温室气体减排和全球气候变暖减缓上做出了巨大贡献.经济林营造采用精准施肥和为退耕还林工程区农户提供可替代的维持生存的方法是分别减少碳成本和碳泄漏的可能措施.
Keywords: Grain for Green Program (GPP); carbon cost; carbon leakage; greenhouse gas; net carbon sequestration.