中国木质林产品碳贮量

Carbon stock of harvested wood products in China

一直以来，在国家温室气体清单的计量中，均假定森林采伐后其贮存的生物量碳在采伐年全部释放进入大气。实际上，森林采伐后形成的木质林产品中的碳并没有立即排放。而是在随后的数年或数十年间逐渐排放，部分以垃圾形式填埋的废旧木质林产品中的碳还可能得到长期保存。但是，由于不同的计量方法导致计量结果的不确定性，木质林产品碳贮量变化是否纳入国家温室气体清单土地利用、土地利用变化和林业（LULUCF）部门的计量和报告，还存在很大争议。这也是缔约方会议争论的焦点议题之一。许多国家在国家温室气体清单中报告了木质林产品碳贮量。采用IPCC好的做法指南提出的碳贮量变化法、大气通量法、生产国法和一阶衰变法计算了我国木质林产品碳贮量及其变化，比较了不同方法和不同数据源（我国统计数据和联合国粮食和农业组织（FAO）统计数据）计算得到的碳贮量的差异，并分析了产生差异的原因。结果表明：（1）我国木质林产品碳贮量一直处于增长趋势，1900—2003年年均增长量为2．25×106MsC·a^-1，随着木质林产品消费量的增加，2020年碳贮量将达到6.14×IOsMgC。（2）3种计量方法计算结果差异显著，用碳贮量变化法计算2003年的碳贮量为2．35×10^9MgC，大气通量法为O．47×10^8MgC，生产国法为1．79×10^8MgC。由于我国是木质林产品生产及进1：1大国，运用碳贮量变化法，1900—2020年间碳贮量年变化的平均值比生产国法多1．17×10^6MgC，比大气通量法多5．66×10^6MgC。（3）用FAO数据计算我国2003年碳贮量，其结果是我国统计数据的2—7倍。

In the national greenhouse gas inventory, the carbon stock in biomass of forests after harvesting has been assumed to release immediately in the year of harvest. Actually the carbon in harvested wood products （HWP） made from harvested forests does not release immediately after harvest, and instead it will decompose gradually in the following years. Some of them can even be conserved in the terrestrial ecosystems if the waste HWP goes into landfill. However, since different accounting approaches may result in quite different results, whether or not carbon stock change in HWP will be included in the estimation and reporting of the land use, land use change and forestry sector in the national greenhouse gas inventory is still pending and has been debating issues in the negotiation of the Conferences of Parties. Many countries have voluntarily estimated and reported the carbon stock in HWP in their national greenhouse gas inventories. In this paper, three approaches （Stock-change, Productions and Atmospheric-flow） and the first order decay method developed by IPCC were applied for estimating the carbon stock changes in HWP of China. The carbon stock changes in HWP resulting from different approaches and data sources （ national statistics and FAO data set） are compared and analyzed. The results show that the carbon stock in HWP had been increasing in China since 1900 with an annual mean increase of 2.25 × 10^6MgC·a^-1 from 1900 to 2003. It was estimated that the carbon stock in HWP of China will be up to 6.14 × 10^8 MgC in 2020 with the increase of the wood products consumed. The carbon stock in HWP varies with accounting approaches applied. Carbon stock estimated by stock change approach is 2.35 × 10^8MgC in 2003, and 0.47 × 10^8MgC by atmospheric flow and 1.79 × 10^8MgC by production approach. Since China is the largest wood import country, the mean annual carbon stock change in HWP from 1900 to 2020 estimated by stock change approach is 1.17 × 10^6MgC more than production approach and 5.66 × 10^6 MgC more than atmospheric-flow approach. FAO data set resulted in significant larger carbon stock in HWP, compared to China＇ s data set. Carbon stock in HWP in 2003 estimated using three accounting approaches and FAO data is 2- 7 times of China＇ s data set.