Report - ICP Forests

3. Intensive Monitoring 73
Element source Number
of plots
Logaritmised?
Outlier
corrected?
Skewness
after
correction
Na throughfall 278 yes no -0,502
Cl throughfall 278 yes no -0,665
NH4 throughfall 278 yes no -0,869
NO3 throughfall 278 no no 1,199
SO4 throughfall 278 no no 1,61
Ntot throughfall 278 no no 1,36
NH4 calculated 265 no no 1,623
NO3 calculated 265 no no 1,454
Ntot NH4+NO3 (calc.) 265 no no 1,51
Deposition data
Deposition was calculated as the product of rainfall or throughfall quantity per two- or fourweek
period and the concentration per element over that period, and recalculated to yearly
averages. Deposition per plot was determined as the average of the years where sufficient data
were available. Only those years were included that had data for at least 80% of that year. In
many cases, there were missing values for individual elements, specifically for NH 4 , and this led
to many missing years. Among the 619 plots with both vegetation and soil data, there are 414
with bulk deposition data, 278 with throughfall data, and 265 with both. An overview of the
numbers of plots with either bulk or throughfall data, and their pre-treatment, is given in Table
3.4.2-4B. These plots have deposition measured over periods that differ in length and position in
time, but as trends in N deposition were not significant, we assumed that the years for which
deposition data are available are a good estimate for the deposition over the period where
vegetation data are available.
Because measured deposition was available for only a subset of all plots, deposition estimates
for NH 4 , NO 3 and SO 4 for 1995, 2000 and 2010 were also derived by overlaying the plot
locations with results of the Eulerian atmospheric transport model of EMEP/MSC-W at a 50 km
x 50 km grid cell size (Tarrasón et al., 2007). Annex 3.4.2 gives the correlation coefficients
between EMEP deposition estimates for 2000 and measured bulk and throughfall deposition.
Correlations coefficients are in the order R ≈ 0.6 for both N and S. For both EMEP estimates
and bulk and throughfall deposition, N-total was calculated as the sum of NH 4 + NO 3 . In
addition, dry deposition of NH 4 and NO 3 was estimated on the basis of the difference between
bulk and throughfall deposition, assuming a conservative behaviour of Na; this is referred to as
'calculated' deposition.
Other data
Climatic zones were assigned to each plot on the basis of its geographical position according to
De Vries et al (2002). Moreover the following data were taken from the database:
- country;
- latitude and longitude;
- stand age (classes recalculated to 'real' age as code * 20, code 8 ('irregular stands') replaced by
70);
- altitude (classes recalculated to 'real' altitude as code * 50 and logarithmised to correct for
skewness);
- tree species: these were clustered as presented in Table 3.4.2-1. For Quercus, the temperate
and mediterranean species were taken together. Pinus sylvestris and P. nigra were taken
together. Fagus sylvatica and Picea excelsa were used as such. All other species were lumped to
'coniferous' and 'deciduous'.