Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Improved regional and national level estimates of the carbon stock and stock changes of tree biomass for six European countries

The 'top-down integration' applies existing forest inventory data in their aggregated form (for example, tree species or tree species group per region in a country) for forest area, standing volume and increment. Volume estimates were expanded to total tree biomass carbon estimates per tree species and age class by using biomass expansion factors (BEFs) from WP2 ("Biomass Expansion Factors").

Carbon budgets were calculated for the six European countries (Austria, Finland, Sweden, Spain, Ireland and Germany) using an existing modelling framework, the European Forest Information Scenario Model EFISCEN. The EFISCEN model was run until 2015, assuming that harvest levels would remain constant after 2005. Carbon stock changes were calculated from stock changes over the period of time considered. The BEFs developed for Finland were also used in Sweden, and those developed for Germany were also used in Austria. BEFs for Spain were not age-specific, due to the lack of suitable data. Data were also scarce for Sitka spruce and Lodgepole pine; the most abundant tree species in Ireland, therefore biomass functions developed in America were applied for these two species.

Initial (1995) biomass carbon stocks ranged between 25 and 50 Mg C ha-1 in Spain, Ireland, Sweden and Finland, and between 100 and 110 Mg C ha-1 in Germany and Austria. Differences in the mean carbon stocks per hectare can be related to the mean volumes per hectare. High per hectare volumes in Germany and Austria resulted in high biomass carbon stocks compared to the other countries. In all of the six test countries, carbon stocks increased over time. It was assumed that no changes in the forest area occur during the simulation period; therefore, the trend of the carbon stocks is affected only by fallings and by ageing of the forests.
The accuracy of the results for the biomass carbon stocks depends greatly on the quality of the utilised inventory data, and on the adequacy and representativeness of the applied biomass functions. The quality of the forest inventory data varies between countries. Adequate biomass functions were available for boreal conditions, as well as spruce, beech and pine in central Europe, but representative data for other species/regions was scarce. Biomass carbon stock changes depend on the difference between increment and fallings. While average increment rates usually do not change drastically over the course of 20 years when large forest areas are considered, felling levels depend on many fluctuating factors such as market prices, wood demand and the occurrence of natural disturbances like storm. Therefore, our modelled tree biomass changes may deviate considerably from reality.

In the EFISCEN modelling framework, the soil carbon stocks are assessed with a modelling approach, where tree carbon pools are combined with compartment-specific turnover rates to estimate the litter input to the soil. This litter is given as input to the dynamic soil carbon model YASSO, which simulates litter decomposition. Mean soil C stocks ranged between 60 and 90 Mg C ha-1 in Spain, Ireland, Finland and Sweden, and were around 130 Mg C ha-1 in Germany and Austria. National soil carbon estimates from WP3 ("Soil carbon inventories") were 50-70% lower than our modelled values for Finland, Sweden, Germany and Austria.

For Ireland and Spain, the soil carbon estimates from WP3 were higher than our model results. Among the possible explanations for the variation between model results and soil carbon estimates are:
-the fact that WP3 only considered carbon down to 20cm, while YASSO is assumed to simulate soil carbon down to 1m,
-the equilibrium assumption in Yasso, which is unrealistic in the light of past changes in forest management and environmental conditions, and
- the overestimation of decomposition rates on organic soils within YASSO, which leads to low soil carbon estimates in countries where a large share of the forest grows on peat-land (e.g. Ireland). Soil carbon stock increased over time in all test countries, with an annual change of around 0.01 Mg C ha-1 in Finland, Germany, Spain and Sweden, almost 0.3 Mg C ha-1 in Ireland, and 0.8 Mg C ha-1 in Austria. The high increase in Austria was caused by the strong increase in simulated growing stock, which resulted in more litter-fall. However, we probably underestimated fallings in Austria, and therefore the stock change should be regarded with care.

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