Report - ICP Forests

3. Intensive Monitoring 81
-0.6 0.6
Cratamon
Castasat
Acer pla
Ranunfic
Carpibet
Rumexsan
Ribesalp
Viciasep
Quercrub
Sorbutor
Oxaliace
Axis 2
Lat
Impatpar
Hellefoe
Querccer
Malussyl
Polypvul
Prunuavi Pteriaqu
Sorbuauc
Rosa arv Rubusfru
Rumexact
Rubuscae
Potenste
Ulmusgla
Sorbudom
Quercpyr Geum urb
Urticdio Mercuper
Anemonem
Lathyver
Axis 1
Rosa can
Fragaves
Geranrob
Cardaimp
Acer cam
SubAtl_Cli
Lathyven
pH_org
Ndep95_EMEP
-0.2 0.8
Figure 3.4.4-2: Biplot of the model of Table 3.4.4-6. See caption of Table 3.4.4-6 for details. Explanation of
species codes in Annex 3.4.1, explanation of environmental codes as in Figure 3.4.4-1 (SubAtl_Cli = subatlantic).
Species are selected for which > 2% variance is explained by the model.
Temporal change in the Ellenberg values and number of species
Table 3.4.4-7 gives the change in Ellenberg values and their significance. The indicator for
nutrient availability (N) is the only one that significantly changed (increase, P = 0.01). Besides,
the number of species per relevé highly significantly increased by 1.4 species (P < 0.001).
Multiple regression was used to find the relation between the environmental variables and the
change in those indicators that significantly changed (Ellenberg N and number of species). A
minimal model was derived by backward selection, i.e. stepwise removal of non-significant
terms from a full model containing all environmental variables, until only variables with a
significant effect remained. Also terms with a correlation of |R| > 0.5 with other terms in the
model were removed, starting with the one with the lowest T-value. Again this was done with
(N = 99) and without (N = 42) bulk and throughfall deposition (in this case the number of usable
records is even lower than in the multivariate analysis because at both points in time (first and
last relevé) there should be at least three species with a known Ellenberg value). Table 3.4.4-8
gives the result when only EMEP deposition estimates are included, and Table 3.4.4-9 when
both bulk, throughfall en EMEP deposition are included. In both cases there is a significant
effect of N deposition, even for both EMEP and throughfall when they are included together (in
this selection their R is just < 0.5). Both terms influence the change in Ellenberg N in the
expected direction i.e. an increase. Note that the large negative value for the 'undetermined' fit is
due to interaction effects which have not been explored in this project. Therefore the models
(especially of Table 3.4.4-9) should be viewed with some caution. Table 3.4.4-10 gives the
analysis for the change in number of species; the EMEP deposition does not significantly
contribute to this change.