Proceedings zur 6. Fachtagung BIOMET - Deutsche ...

WIDLOWSKY et al., 2003, and for spruce trees as in KURTH AND SLOBODA (1999, Fig. 2). The
spectral properties of phytoelements at this stage were used: a) for spruce trees - as mean sun
twig for upper crown part and as a mean shade twig for lower crown part, the age differences
were nor considered; b) for all deciduous species the spectral properties of average sun and
average shade leave of beech as measured in Solling, B1 were used.
3. Results
3.1 Model validation
The model was validated for different forest stands (KNYAZIKHIN et al., 1997, PANFEROV,
2005) and showed a very good agreement with observations. In present study only the additional
validation for a gap and forest edge was carried out. The results have shown a very
good agreement between modelled and measured radiation for typical meteorological situations.
In Fig. 3 the comparison between measured and modelled fluxes of short-wave radiation
is presented for central (“gap”) and western (“edge”) meteostations.
Abb. 3: Vergleich eines gemessenen und modellierten Tagesgangs der kurzwelligen Strahlung
an der zentralen Messstation (links) und am Westrand der Freifläche (rechts)
Fig. 3: Comparison of measured and modeled daily course of global short-wave radiation at
central meteostation (left panel) and at western border of the clear cut (right panel)
3.2 Effect of inclination
Preliminary results – the radiation distribution within the studied area of Otterbach clear-cut -
were already presented in (PANFEROV et al., 2006). Therefore, we would like to focus here on
the effects of northern slope especially within the forest – clear-cut transition zones as compared
to the horizontal stand.
As expected even the very gentle inclination with northern exposition decreases considerably
in general the intensity of radiation at soil surface. To characterize the changes we used the
normalized difference δ(r)=(Ih(r)-Is(rs))/Ih,(r). Ih(r) is the intensity of radiation at horizontal
surface in the point r(x,y,z) of model domain and Is(rs) is the intensity of radiation at the sloping
surface at the point rs (x,y,z+Δz) with the same horizontal coordinates (x,y) as the point r,
at same moment of time (time period) and under the same illumination conditions. Considering
the “time period” as an entire vegetation period the estimated δ was on average about 0.1
(Fig. 4), i. e. the northern slope was “underilluminated” by about 10% comparing to horizontal
surface. The result is completely in accordance with a theory predicting the alteration of
radiation incoming to the bare slopes (e.g. KONDRATYEV, 1969). However, the presence of
rather complicated vegetation – forest stands with a clear-cut - changes that simple theoretical
distribution pattern considerably. Fig. 4 illustrates the frequency distribution of δ�for different
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