Carbon stock quantification - How sure can one be?
Carbon stocks and stock changes quantification, including an estimate of uncertainties, has been performed at regional and national levels. Whole tree biomass and soil C- stock and stock changes estimates were produced employing a combination of aggregated forest inventory data with biomass expansion factors (top-down approach). The results were validated using Monte Carlo simulation to calculate uncertainty estimate of C-stocks and stock changes of tree biomass and forest soils. In specific, two models were employed; a large scale Forest scenario model (EFISCEN) and a dynamic soil model (YASSO) using data from four countries. Uncertainty analysis gave estimates of biomass, soil C-stocks and stock changes by combining the two models. During all analyses, sources of uncertainty estimates e.g. biomass allocation, turnover rates, etc. were taken into account. Biomass uncertainty analysis involved conversion of inventory data to total biomass and then to carbon. In stock change analysis, Monte Carlo simulation was performed under the assumption that data came from the initial and final inventories. Soil carbon uncertainty estimates were assessed by converting biomass estimates to woody litter which was given as input in YASSO soil model for decomposition simulation. The results revealed that biomass C-stock uncertainty is inversely proportional to stock change while C-stock change estimate for soils is more reliable compared to soil C-stock assessment. In addition, soil C-stock uncertainties are similar between countries as assumed in the relevant model. The impact factor of the selected soil model on the overall carbon assessment was also evaluated. The results showed that differences between models were site and species dependent and underlined the impact of reduced data availability on quantifying uncertainty. Dynamic models like the aforementioned could prove useful tool for monitoring the overall carbon content before adopting new practices in forest management and strategic planning at national level.
