退耕还林工程不同造林类型温室气体收支与净碳汇--以中国中南及华东地区为例

Greenhouse Gas Budget and Net Carbon Sequestration of Different Afforestation Types Used in Grain for Green Project-A Case Study in Central South and East China

[目的]揭示退耕还林工程温室气体泄漏对工程固碳减排的抵消作用,明确工程不同造林模式对固碳减排实际贡献的差异和空间格局。[方法]针对退耕还林4种类型造林(即生态林、经济林、用材林和薪炭林)构建了碳核算与净减排评估方法(CANM-GGP),通过核算典型树种造林的植被和土壤固碳、伐后产品固碳和生物质能源替代化石能源减排等固碳减排效应,以及造林和经营管护的温室气体泄漏,对中南及华东地区退耕还林工程4种类型造林的净碳汇进行评估。[结果]2000-2019年,中南及华东地区退耕还林工程的生态林、经济林、用材林固碳和薪炭林减排总计648.43 Tg(以CO_(2)计),同期工程带来温室气体泄漏96.43 Tg,抵消总固碳减排的14.87%;不同造林类型的温室气体泄漏中,经济林最多,为57.69 Tg,抵消其固碳效应的73.95%;温室气体泄漏分别抵消生态林、用材林和薪炭林固碳减排的5.75%,16.59%和27.05%。工程平均单位面积净碳汇为4.52 t/(hm^(2)·a)(以CO_(2)计);各省区在2.85~5.74 t/(hm^(2)·a)之间;生态林为5.52~8.89 t/(hm^(2)·a),经济林为0.72~1.56 t/(hm^(2)·a),用材林为0.8~1.61 t/(hm^(2)·a),薪炭林为3.18~5.99 t/(hm^(2)·a)。[结论]中南及华东地区退耕还林工程取得了巨大的净固碳减排效益,生态林固碳增汇效果明显,净减排效益最显著,生物质能源替代化石能源燃烧减排的效益非常可观。作为最大的温室气体泄漏因素,化肥相关的温室气体排放对生态工程碳汇的抵消影响不容忽视。

[Objective]The offsetting effects of greenhouse gas(GHG)leakage on carbon sequestration and GHG mitigation in the grain for green project(GGP)were analyzed in order to clarify the difference and spatial pattern of actual GHG sequestration and mitigation contribution of different afforestation types to GHG sequestration and mitigation.[Methods]A method for the GHG budget accounting of different types of afforestation(including ecological forest,economic forest,timber forest,and firewood forest)under GGP(i.e.,carbon accounting and net mitigation-GGP)was established.Carbon sequestration effects of afforestation were estimated for selected typical tree species in vegetation and soil.Carbon sequestration of post-logging products and mitigation of fossil fuel substitution by biomass energy were determined.GHG leakage caused by afforestation and management was also determined.The net carbon sequestration of the four afforestation types in GGP in Central South and East China was then evaluated.[Results]The carbon sequestration of ecological forest,economic forest,and timber forest,and the mitigation of firewood forest amounted to a total of 648.43 Tg(CO_(2))during the period from 2000 to 2019 in Central South and East China.Additionally,the total GHG leakage of GGP reached 96.43 Tg,which could offset 14.87%of the total carbon sequestration and mitigation.The economic forest produced the largest GHG leakage,which reached 57.69 Tg,offsetting 73.95%of its carbon sequestration.The GHG leakage offset 5.75%,16.59%,and 27.05%of the carbon sequestration or mitigation effect of ecological forest,timber forest,and firewood forest,respectively.The average net carbon sequestration per unit area of GGP in this region was 4.52 t/(ha·yr)(CO_(2)),ranging from 2.85 t/(ha·yr)in Guangxi to 5.74 t/(ha·yr)in Anhui.The net mitigation rate of GGP was 5.52~8.89 t/(ha·yr)for ecological forest,0.72~1.56 t/(ha·yr)for economic forest,0.8~1.61 t/(ha·yr)for timber forest,and 3.18~5.99 t/ha/yr for firewood forest.[Conclusion]GGP in Central South and East China has achieved huge net carbon sequestration and emission mitigation benefits.Ecological forest had an obvious effect on carbon sequestration,and the net mitigation benefit was the most significant.Biomass energy could replace fossil fuel combustion and its mitigation benefit was also very considerable.The influence of fertilizer-related GHG leakage on ecological engineering carbon sequestration cannot be ignored.Fertilizer-related GHG emissions and their offsetting effect on carbon sequestration in the ecological project were nonnegligible because it was the largest GHG emission factor.