EFI : European Forest Institute
Le réseau pour la gestion durable des forêts cultivées.

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FORSEE : Indicateur évalué

Indicator 1.4.1: Carbon stock in the woody biomass
Forest area covered (1995):
4956,1 ha

Percentage of the total forest
area in Sousa Valley: 14,3 %

No of plots: 35



1227,3 €

Costs/ha: 0,24 €

Costs/plot: 35 €

The total cost includes:

1- Data collection: 959 €

2- Data analysis: 268,3 €


Method 1: Biomass equations (Fabião, 1986; Lopes, 2005)


Sources: Fabião, 1986; Lopes, 2005.

Method 2: Conversion and expansion factors


Sources: UTAD

Sistematic grid, n = 35 plots


The Portuguese Institute of Environment (Instituto do Ambiente) gives 0,70 and 0,78 as the conversion and expansion factors that should be used to esteem the aboveground dry biomass from stem volume in Eucalyptus globulus and Pinus pinaster, respectively. The value found by UTAD researchers for Pinus pinaster is different (0,54 instead of 0,78). One suggests the use of 0,54 for the pine species since one considers it more reliable.

Problems and improvements

Method 1 can have problems if applied for all the existing species because there are no models for non representative species found in the plots of the pilot zone (e.g. Quercus species).

Method 2 has more problems. In short, the following can be pointed out:

a) Not all the tested procedures to estimate biomass from volume are general enough.

A new proposal that considers “mixed” and “pure” stands with woody biomass from other species is presented at the FORSEE REPORT, PART 2: MATERIAL AND METHODS.

b) Reliable conversion and expansion factors,  and E, are needed, since they are not constant values (a deep study is being developed at the University of Trás-os-Montes e Alto Douro for Pinus pinaster).

c) Estimation smoothing allows a narrower confidence interval (but that does not imply a higher accuracy).

d) A clear definition of what is being “converted” and what is being “expanded” should be clearly stated in all studies for comparison of the results.

It should be given more attention to the underground component of biomass either for data collection or for the development of models.

Comments and conclusions

The use of individual tree allometric biomass equations with raw forest inventory data is an expedite process to estimate woody biomass. It is easier to process data and the process is compatible with forest inventories at local, regional or national level. The main inconvenience is that it requires the availability of “good” models for all the forest species existing at the forest plots.

The estimation of biomass from volume is a low-cost alternative for tree biomass equations. When tree inventory data is missing, it could be the only method that foresters and ecologists have to get an estimation of woody biomass. Nevertheless, its “friendly use” might not be a reliable alternative as current users may think. Therefore, the results should be analysed carefully. Further studies on this subject should be developed.

Carbon stock is one of the indicators of Criterion 1 considered by NP 4406 2003. NP 4406 2003 considers that one of the main functions in the forest ecosystems is the capacity of being a carbon sink. The increase of volume of the forest stands has positive consequences in the behaviour of this indicator though the effectiveness of this function is strongly limited by the use given to the products extracted from the forest.

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