International carbon accounting of harvested wood products: evaluation of two models for the quantification of wood product related emissions and removals

At the moment three alternative approaches for estimating emissions and removals of CO2 from forest harvesting and wood products are under discussion. These are atmospheric flow approach, stock change approach, and the production approach. Several methodologies are being developed to deal with these approaches. In the present report we test two of those The 'Forest Research Institute from New Zealand has developed an Excel based model' (FR), and the FA model (Alterra supported by FORM Ecology Consultants). The IPCC approaches themselves are not under study here, only the models representing them. Above that, a sensitivity analysis of the data input has been done, with a special focus on life spans. The models are qualitatively and quantitatively compared , and a sensitivity analysis on life spans was carried out. In principle both models (FR & FA) are very comparable, and can in principle be used as a basis for improved IPCC guidelines in this area. However, the current FR model focuses on the carbon dynamics in the long life span products only (on purpose), and thus lacks the following sources of CO2: actual burning of fuelwood (in atmospheric flow and production approach), immediate decomposition of wood residues (in atmospheric flow and production), and harvest figures (in stock change approach), which are relevant for determining the overall wood products carbon balance of a country. Thus the results of a full quantitative comparison of the FR and FA model were not so relevant. Finally, it is noted that the production approach can be interpreted in different ways. A wide variety of life span estimates was found in literature. Different shapes of decay functions are used. Also, confusion can occur because the half lives, total lives, as well as in- or excluding the disposed off phase, are used in literature. This contributes a lot to the uncertainty regarding life spans. The carbon balance of wood products showed the strongest sensitivity to life spans for New Zealand and The Netherlands. Especially the production approach is sensitive for changes in life spans. The overall effect of a decrease in life span is an increase of the sources, or in the case of The Netherlands under the stock change approach, a change from sink to source