Application of the stock change and the production approach to Harvested Wood Products in the EU-15 countries: a comparative analysis

Abstract

With the analytical tool: Frankfurt Harvested Wood Products (HWP) Model, carbon stocks and carbon stock changes of HWP, either in USE or in LANDFILLS, have been evaluated from the readily available statistical data base of the FAO, FAOSTAT, on the wood commodities: “Sawnwood and Wood-based Panels” and the paper commodities: “Paper and Paperboard”. Essential differences have been found between the individual 15 EU countries in the comparison of the Stock Change Approach and the Production Approach, as well as in the comparison of the stock changes of HWP with the National Greenhouse Gas (GHG) budgets. The stock changes for the HWP in USE within the EU-15 Community have been calculated to be 10.83 Mt C/a (39.71 Mt CO₂/a) based on the Stock Change Approach and 9.81 Mt C/a (35.97 Mt CO₂/a) for the Production Approach, respectively. These numbers can be compared to the total GHG Inventory of the EU-15 of 4,095 Mt CO₂ equivalents, including all six Kyoto gases, which shows that the carbon sequestration of HWP in USE is of the order of 1% relative to GHG Inventory. The GHG balance for the carbon stock changes of HWP in LANDFILLS is of similar magnitude as for the HWP in USE, and therefore a sink when methane outgasing is disregarded. However, when methane outgasing is considered, which is formed as a 1:1 mixture with CO₂ under the prevailing anaerobic conditions the GHG balance results in minus 10.0 Mt C equivalent/a and minus 10.6 Mt C equivalent/a for the Stock Change Approach and the Production Approach under the parameters chosen in this study.

Appendix

Four country comparison between the analytical and the numerical calculations for the stock change approach.

Table 7 refers to the calculations for the countries: Austria, Finland, Germany, Portugal and the EU-15 which have been studied in particular depth. It shows that the agreement between the two calculation methods is excellent, except for the calculated annual carbon change of the HWP in USE. Columns B–D are input data of the calculations, with reference to the year 2000. The analytical approach uses exponentially smoothed data, which are different from the annual input data of the numerical method. Columns E–K are results of the calculations: The ultra-simple calculation procedure of the analytical approach is given in the column heading, as described in the paper above. The numerical calculation procedure is the stepwise Euler integration either in the explicit form, called forward integration or in the implicit form, called backward integration. Starting with the integration of the differential equation of the form:

$$ {\text{d}}x/{\text{d}}t = F_{{{\text{in}}}} (t) - k_{{{\text{out}}}} x(t) $$

(9)

as described previously by Pingoud (2002), where x(t _i ) stands for stock of HWP either in USE or in LANDFILLS at time t _i and where F _in(t _i ) stands for HWP production (or consumption) or waste production in the year t _i .

Table 7 Stock change approach: four country comparison including EU-15 between the analytical and numerical calculations for the stocks and stock changes of HWP of the category “Sawnwood and Wood-based Panels” (year 2000)

Forward integration, with time step 1 year: t ₂ − t ₁ = 1, yields

$$ x{\left( {t_{2} } \right)} - x{\left( {t_{1} } \right)} = F_{{{\text{in}}}} {\left( {t_{1} } \right)} - k_{{{\text{out}}}} x{\left( {t_{1} } \right)} \to x{\left( {t_{2} } \right)} = F_{{{\text{in}}}} {\left( {t_{1} } \right)} + {\left( {1 - k_{{{\text{out}}}} } \right)}x{\left( {t_{1} } \right)} $$

(10)

while backward integration, which is preferred here, leads to:

$$ x{\left( {t_{2} } \right)} - x{\left( {t_{1} } \right)} = F_{{{\text{in}}}} {\left( {t_{2} } \right)} - k_{{{\text{out}}}} x{\left( {t_{2} } \right)} \to x{\left( {t_{2} } \right)} = \frac{1} {{{\left( {1 + k_{{{\text{out}}}} } \right)}}}{\left\{ {F_{{{\text{in}}}} {\left( {t_{2} } \right)} + x{\left( {t_{1} } \right)}} \right\}} $$

(11)

It can be seen from column E that the agreement between the two approaches is within 1% for the HWP stocks of sawnwood and wood-based panels. The cumulative procedure in determining the stock in the numerical method shows that nearly any differences between the two methods are wiped out. The stock changes for the year 2000, shown in column F, are in contrast, quite different for the two methods, and can differ by as much as 50% (see Finland).

However, when the numerical annual changes are plotted as a function of time and smoothed and fitted to an exponential function, a posteriori, the results of the analytical method can be reproduced. Columns G–I give the HWP stocks in LANDFILLS, for two cases. Case 1: the stocks are already in a stationary state in the year 1900 (column G) or case 2: The stocks are 0 in 1900 (I); the difference between the two cases is given column H. The stocks calculated by the two methods do not differ by more than 2%. Column J gives the annual change in landfills, which is here much less different for the two approaches as the stocks have been smoothed through the inputs which depend on the stocks of the HWP in USE. Similar considerations are valid for GHG balance with methane outgasing, except that the calculated difference between two small numbers can result in seemingly larger differences between the two methods. The last row shows the agreement with the calculations of Pingoud (2002) for Austria, which were obtained under slightly differently chosen parameters.