Potentiale zur energetischen Nutzung von Biomasse in der ... - EPFL

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It may happen that measurements of trees upper diameter and height are missing while measurements
of diameter at breast height could be available for specific forest stand. In this case, the total volume of
biomass could be calculated using another NFI methodology, the so-called “tariff functions”. These
functions estimate individual tree volume depending only on one measured variable (dbh 1.3 ). A more
precise evaluation can be obtained if additional trees and site attributes are taken into account. Details
of this methodology can also be found in WSL 2001.
Finally, it is possible that for some forest stands the total volume of available biomass has already been
estimated. In that case this volume has to be allocated to different tree species or generalised species
groups (deciduous/coniferous). Another important variable to be estimated at this stage is the
proportion of individual pixel’s surface which is being occupied by particular tree species.
Estimation of harvestable amount of biomass
Since the whole amount of available biomass resources can not be harvested at once without prejudice
to the forests’ ecological balance, therefore a complementary factor of ecological availability should be
introduced in order to estimate the harvestable quantities. Such a factor could roughly correspond to
the estimated annual increment in standing trees volume. This factor can be calculated according to the
following formula:
where
AF ij : ecological availability factor of particular tree species i at given pixel j
AF
GR jk : annual growth rate of particular tree species at a given type of location (m 3 /ha*yr)
S ij : territory on a given pixel’s surface being actually occupied by particular tree species (ha)
Q ij : total volume of biomass of particular species at a given pixel (m 3 )
ij
GRik
× S
=
Q
The determination of the annual growth rate of particular tree species can be based on three criteria: (1)
the vegetation storey, as a function of altitude, orientation and soil properties, greatly influences tree
growth. Guidelines for determination of particular type of vegetation storeys across different geographic
locations are given in Annex 11; (2) the tree growth also varies with the general type of forest, i.e.
coniferous for at least 90% of the stems, deciduous for at least 90% of the stems or mixed; (3) finally,
since trees of different ages do not grow at the same pace, age classes were taken into account. The
chosen stand categories are young (≥90% of the stems with a size of 0–10 cm), middle-aged (≥ 90% of
the stems between 10–16 cm), mature (≥ 90% of the stems greater than 16 cm) and uneven aged
(mixed). Annual growth rates are given according to these conditions in Table 46.
ij
ij