土地利用变化和林业活动碳贮量变化测定与监测中的方法学问题

土地利用、土地利用变化和林业 (L U L U CF)活动是引起大气温室气体浓度上升的主要因素之一 ,评价、监测 L UL UCF活动的碳源 /汇功能还存在很大的不确定性。近年来我国在该方面开展了一些研究和测定工作 ,但研究力度还远远不够 ,研究方法还存在一些问题。针对 L U L UCF活动对碳贮量影响的测定和监测中的碳库选择、监测间隔期、样地数量以及土壤容重影响和校正等有关方法学问题进行了阐述 ,以期为我国该方面的研究和监测有所裨益。

Methodological issues related to measuring and monitoring carbon stock changes induced by land use change and forestry activities

Human-induced land use, land use change and forestry (LULUCF) activities are believed to be one of the most important factors contributing to rising greenhouse gases in atmosphere and global climate change. To accurately assess the impacts of LULUCF activities on atmospheric carbon is vital for human being to develop, implement and evaluate policies and measures against the climate change. Periodic measuring and monitoring carbon stock changes is a key method to achieve this. However, great uncertainties exist in assessing and monitoring the carbon stock changes caused by LULUCF activities over the world. Although some measuring and studying works have been conducted on this aspect in China in recent years, the quantity is far from needs and the methods used are questionable to some extents. This paper discussed some methodological issues used in measuring and monitoring carbon stock changes of LULUCF activities, including choice of carbon pools, monitoring interval, sampling intensity, soil bulk density effects and its correction, hoping to provide methodological references for related measuring and monitoring in China. We believed that selected carbon pools to be monitored, length of monitoring interval and number of samples are closely linked to both monitored precision and cost. There is a trade-off between the precision and cost. The increase either in carbon pool, monitoring frequency or sample intensity would inevitably raise the monitoring cost. Therefore a balance needs to be found between the precision and cost. This should be determined on the basis of statistic theory through the size of pools, rate and direction of changes, and variations of pools in both time and space dimensions. Moreover, land use changes usually cause changes in soil bulk density, resulting in errors of monitored changes of soil organic carbon. To avoid the errors, it was recommended that soil bulk density should be measured and sampling depth should be calculated before sampling. In case sampling has been implemented with a fixed soil depth, a correction procedure should be conducted to eliminate the impacts of bulk density changes.