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Appendix S1 Details on the methods
Choice of Evenness Metrics
We selected Evar to estimate evenness because it is independent of species richness and is symmetric with
regards to rare or dominant species (Smith & Wilson, 1996). It was calculated using to the following
formula:
𝑆
𝑆
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𝐸𝑣𝑎𝑟
2
2
= 1 − 𝑎𝑟𝑐𝑡𝑎𝑛 ∑ (ln⁡(𝑥𝑠 ) −⁡∑ ⁡ln(𝑥𝑡 )/𝑆) /𝑆
𝜋
𝑡=1
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( 𝑠=1
)
Where xs and xt are the cover values of species group s or t, respectively, and S is the number of species in
the vegetation plot. Evar is not impacted by richness or symmetry because it is based solely on variance in
species' abundances (Smith & Wilson, 1996).
Estimation of deposition data
Deposition data were extracted from the EMEP data base (http://www.emep.int) with a resolution of
50 km × 50 km. We used wet and dry deposition data of reduced and oxidized N and for the year 2000
(N2000, expressed in kg/(ha * year)). De Schrijver et al. (2011) showed that the modelled EMEP data and
locally observed N deposition data are very well correlated. Significant underestimations only occur at
sites where nearby point sources (e.g. large animal husbandry farms) are present. However, through fall
N-deposition on the forest floor will likely be between 1.5 to 2 times greater than in open fields due to the
high aerodynamic roughness of forest canopies (ICP, 2005).
To obtain accumulated N-deposition between the two surveys, we accounted for variation in deposition
rates over time by calculating the cumulative deposition between the two survey years using correction
factors for the different decades based on the year 2000 deposition rates (see Dupre et al., 2010 for more
information on the correction factors and the calculation methods).
The amount of N already deposited at the time of the baseline vegetation survey was calculated as the
cumulative deposition between 1900 and the year of the initial survey using the correction factors
mentioned above. The amount of N already deposited at the time of the re-survey was calculated as the
cumulative deposition between 1900 and the year of the re-survey, again using the correction factors
mentioned above.
Accumulated sulfur deposition between the surveys and at the time of the baseline survey were not
included in the analysis, as they were observed to be strongly correlated with the corresponding nitrogen
deposition values (Sacc vs. Nacc : r=0.98, t-value = 28.7, p-value < 0.001, n = 38; Sdelta vs. Ndelta: r = 0.99, tvalue = 201.5, p-value < 0.001, n = 38).
Combining species cover values to total layer cover
Total layer cover was estimated based on all occurring species using the following formula (Fischer,
2015):
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with n being the number of occurring species and p their cover values. Total cover estimates are based on
the area not covered by single species, as this may account for species overlap.
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De Schrijver A, De Frenne P, Ampoorter E, Van Nevel L, Demey A, Wuyts K, Verheyen K (2011)
Cumulative nitrogen input drives species loss in terrestrial ecosystems. Global Ecology and
Biogeography, 20, 803-816.
Dupre C, Stevens CJ, Ranke T et al. (2010) Changes in species richness and composition in European
acidic grasslands over the past 70 years: the contribution of cumulative atmospheric nitrogen
deposition. Global Change Biology, 16, 344-357.
Fischer HS (2015) On the combination of species cover values from different vegetation layers. Applied
Vegetation Science, 18, 169-170.
Icp (2005) The Condition of Forests in Europe: Executive Report 2005., Hamburg, Federal Research
Centre for Forestry and Forest Products (BHF).
Smith B, Wilson JB (1996) A consumer's guide to evenness indices. Oikos, 76, 70-82.
REFERENCES
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