采伐对豫西退耕还林工程固碳的影响

以豫西退耕还林工程重点县嵩县为研究对象,收集了嵩县2002—2010年退耕还林工程逐年实施的造林面积、树种等数据,利用合适的人工林蓄积量生长方程和和中国退耕还林后的土壤有机碳变化的研究结果,结合各树种的木材密度、生物量扩展因子、碳含量等参数,在采伐和无采伐两种情景模式下对其退耕还林工程在2002—2050年的碳储量及其变化进行估算。结果表明:2010年,工程林总碳储量为0.470 Tg(Tg=10~(12)g),工程实施期间,工程前期碳储量高于后期;土壤有机碳库在2002—2010年期间年固碳量均为负值,表现为碳排放,2011年后土壤年固碳量开始增加;在两种情境模式下,工程林年固碳量最高峰都在2015年,2033年以后采伐情景的年固碳量大于无采伐情景。预计到2020、2030、2040和2050年,嵩县退耕还林工程在无采伐情境下的固碳增汇潜力分别为0.760、1.464、1.852和1.985 Tg,在采伐情景下的固碳增汇潜力分别为0.760、1.240、1.657和2.000 Tg,从长时间来看,豫西退耕还林工程林在采伐情景下具有较大的碳汇潜力,因此,对退耕还林工程林实施适度的采伐可以提高工程的碳汇能力。

Evaluation of carbon storage and the carbon sequestration potential under cutting and no-cutting scenarios for the Grain for Green Project in Western Henan, China

The Grain for Green Project (GGP), one of the most ambitious ecological projects to be launched in China, was aimed at converting low-yield slope cropland, barren hills, and wasteland into grassland and woodland. The objective of this study was to calculate the carbon stock changes and carbon sequestration potential of the GGP in Western Henan under cutting and no-cutting scenarios, in order to develop a method for further estimation of the carbon sequestration potential of the national GGP and produce a scientific reference for the ecological system management of the GGP in the long run. The Western Henan, one of the major districts that implemented the GGP in China, initiated the GGP in 2002. We analyzed Songxian, which is a major county in terms of implementation of the GGP in Western Henan, as a case to evaluate carbon storage and the carbon sequestration potential under cutting and no-cutting scenarios. We collected data on each year from 2002 to 2010, such as tree species, the planted area of the project in Songxian, the use of a growth curve suitable for China''s planting volume, the findings about the soil organic carbon changes after the GGP together with biomass density of various species, carbon content, the biomass expansion factor, and the estimated carbon storage and annual carbon sequestration for the GGP from 2002 to 2050. The results showed that total carbon storage was 0.470 Tg in 2010, when the project was completed. Total carbon sequestration in the former period is larger than that in the latter period during the project''s implementation. The annual carbon sequestration of the soil organic-carbon pool was negative and released carbon from 2002 to 2010, then an increase in the annual carbon sequestration of soil organic-carbon pool was observed, along with net carbon gains after 2011; the project''s annual carbon sequestration peaked in 2015 under no-cutting and cutting scenarios. The annual carbon sequestration under the cutting scenario is greater than that under the no-cutting scenario after 2033. The potential increment of the carbon sink of the GGP-covered Songxian will reach 0.760, 1.464, 1.852, and 1.985 Tg by the year 2020, 2030, 2040, and 2050 under the no-cutting scenario; it will reach 0.760, 1.240, 1.657, and 2.000 Tg under the cutting scenario. The potential increment of the carbon sink under the cutting scenario will exceed that of the no-cutting scenario after 2050. In the long run, the GGP in Western Henan has a greater carbon sequestration potential under the cutting scenario than that under the no-cutting scenario. Our results suggest that moderate forest harvesting for the GGP can increase the capacity for carbon sequestration.