Denmark's National Inventory Report 2005 - Submitted under the ...

data in detail when the first results from the new sample-based National Forest Inventory are
available in 2007.
So far, the design of the presently used Danish Forestry Census has not made it possible to quantitatively
address uncertainty of inventory data used to estimate the reported sink for CO 2 in Danish
forests. The uncertainty of the volume and increment estimates in the Forestry Census 1990 and
2000 are related to a number of issues: The values of site productivity refer to fully stocked stands
with no border effects and with a given thinning regime. However, a number of these issues are
uncertain. The stands are not fully stocked as the estimates are based on a 90% stocking but it may
be lower. The very fragmented shape of the Danish forest area results in many borders and hence a
reduction in the actual productivity on the area as a whole. Furthermore, the yield table functions
are based on a certain frequency of thinning, which in turn affect the standing volume. With the
changing conditions for the forestry sector, these prescriptions are not followed, which in turn may
lead to deviations, both positive and negative, from the estimated volume and increment. Further
details and alternative estimates can be found in Johannsen (2002) and Dralle et al. (2002).
Other factors also contribute to uncertainty of the reported sinks. As previously mentioned, the
lack of national biomass expansion factors or better expansion functions makes the calculation step
from biomass to total biomass the most critical in terms of uncertainty. Basic densities of wood
from different tree species are better documented and the C concentration is probably the least
variable parameter in the calculations.
In recognition of the difficulties in analyses of uncertainty, the estimated uptake of CO 2 in the forestry
sector must be treated with caution. However, the assessment of uncertainty will improve
significantly from 2007 when the new National Forest Inventory can supply the first national estimate
of stocks of wood, increment and harvest based on a design with permanent sampling plots
and partial replacement. The new design will enable an assessment of uncertainty related to inventory
data.
7.2.3.2 Time-series consistency
The forest area in 1990 and 2000 was not the same for forests existing before 1990 (411,000 and
440,000 ha, respectively). This is due to the nature of the Forestry Census, i.e. there were different
numbers of respondents in 1990 and 2000. We acknowledge the comment by the ERT for NIR 2004
on the complications caused by different numbers of respondents in the Forestry Census 1990 and
2000. The difference in gross uptake of CO between 1990-1999 and 2000-2003 is almost solely due
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to the difference in numbers of respondents to the questionnaire (i.e. forest area) as annual gross
increment per ha was similar for the two periods. However, as mentioned below (Section 7.2.6), we
prefer to avoid recalculations of the present data based on the Forestry Census due to the coming
large revision of the reported data brought on by the new National Forest Inventory.
In addition to this coming revision, we are currently considering to initiate work on a reconstruction
of the land use matrix from 1990 (databases, remote sensing data and aerial photos). This is
necessary in order to be able to apply the same forest definition (FAO-TBFRA) in 1990 as that used
in the commitment period.
7.2.4 QA/QC and verification
QA for the area of existing forests is carried out by Statistics Denmark, and QA for afforestation
area is mainly carried out by the Danish Forest and Nature Agency, as this organisation is responsible
for the administration of subsidies. Harvesting data to support estimates of emissions from
forests existing before 1990 are derived from Statistics Denmark. The QA of harvesting data is
therefore placed under QA within Statistics Denmark. Spreadsheets are in secure files at Danish
Centre for Forest, Landscape and Planning.
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