A repeated soil survey (1995 and 2006) on 66 ICP Forests pair plots in the Czech Republic revealed a significant relationship between modeled nitrogen deposition and nitrogen concentration in the soil. Nitrogen deposition was modeled for the years 1995, 2004 and 2006. We found a more significant relationship between deposition data in 2004 and soil data in 2006 than between deposition and soil data from the same year 2006. Concentration of total nitrogen in forest soil increased from 1995 to 2006. Forest soil showed effects of increased nitrogen input from the humus layer to around 20 cm depth of mineral soil. The occurrence and cover of nitrophilous species in the herb layer increased from 1995 to 2006 in 25% of the analyzed plots, which corresponds to the nitrogen increase in forest soil. The results suggest that nitrogen deposition still represents a threat for Czech forest ecosystems.
During the whole 20th century, a major impact of human activity on the European environment has been reported, especially on forests. In the Czech Republic, the first reports on the negative effect of sulphur emissions date back to the first half of the 20th century (
The effect of N input on the forest ecosystem is complex and disputable - from fertilisation (
The aim of our paper was to evaluate changes in soil chemistry and in ground level vegetation composition caused by N deposition between two forest surveys which were done in the Czech Republic.
Forest vegetation was monitored within the ICP Forests Programme in accordance with
The first survey was done in 1995-1996 within a national inventory by using a national methodology for sampling (
Chemical analysis was carried out in accordance with the standard operating procedures which are recommended by the ICP Forests programme (
The distribution of plots across the Czech Republic is shown in
To estimate the atmospheric deposition of N and H+ ions at selected plots, we used maps produced by adding wet and dry deposition flux maps with a fine spatial resolution of 1 × 1 km. The method was described in detail by
After carrying out the exploratory data analysis, their departure from normal distribution was tested. Data sets were tested as dependent or independent samples (according to input data sets); non-parametric tests (Sign test, Wilcoxon pair test, Kruskal-Wallis ANOVA, Median test) were used, because normality was rejected after Shapiro-Wilk W-test. For testing the relationship between deposition and soil parameters, we also used non-parametric test (Spearman R and Kendall tau correlation). Statistical analysis of the data was performed using the package Statistica® Cz version 12.0 (StatSoft Inc., Tulsa, OK, USA).
Overall, the selected nitrophilous indicator species were identified at 74 out of 154 plots (48%) in 2011. At 39 of these sites, their occurrence was rather sporadic (1-2 species with coverage of up to 0.5%). At 13 sites, the occurrence of nitrophilous species was evaluated as significant (usually more species, though with a relatively low coverage of up to 5%). At 22 sites, there was a significant occurrence of nitrophilous species with a high coverage (above 5%). At other sites (80 plots) the occurrence of nitrophilous species was not recorded. At a total of 38 sites (25%), the presence of nitrophilous species increased during the period analyzed (1995-2011), while a reduction was recorded at seven plots. In addition to the above mentioned species, also
When comparing groups of sites for the occurrence of selected nitrophilous species, there were no statistically significant differences in N concentration (
Soil pH increased (
Differences between the two surveys were significant in nearly all cases (
The difference between total N deposition in 2004 and 2006 was non-significant (
Correlations between deposition in 1995 and soil parameters in 1995 and between deposition in 2004 and in 2006 and soil parameters in 2006 were tested. The results are reported in
In 1995 total N deposition increased with decreasing pH in the humus layer and 0-10 cm mineral soil, while N deposition and N concentration increased
In 2006, we tested the influence of total N deposition and total H+ ions deposition on soil chemistry for the same year of the soil survey (in 2006) and we also tested the influence of deposition calculated in 2004 and its correlation with soil chemistry in 2006. We found more significant results for deposition data in 2004 and soil data in 2006 than for deposition data in 2006 and soil data in 2006. Total N deposition in 2004 increased with increasing N concentration in the humus layer and in the mineral soil at 10-20 cm depth in 2006. Total N deposition in 2004 decreased with increasing C/N ratio in the humus layer and mineral top soil at 0-10 cm in 2006. Correlation between total N deposition in 2006 and selected soil parameters in 2006 was significant only for C/N ratio in the humus layer. Total H+ ions deposition in 2004 was negatively correlated with C/N ratio in the humus layer and mineral top soil at 0-10 cm in 2006. Total H+ ions deposition in 2006 was significant only for C/N ratio in the humus layer in 2006.
During the past 20 years, a higher proportion of nitrophilous species was detected in Czech forests (
Changes in total N concentration in forest soil between the surveys in 1995 and in 2006 and correlation between total N deposition and total N concentration in soil were significant. The relationship between 2004 deposition and 2006 soil chemistry was more significant than the relationship between deposition load and soil chemistry in the same year. This confirms that there is a time lag between the input of the compounds to the forest and their measurable effects on the ecosystem. Results from N deposition measurements across Europe confirm our findings - there is a slight decrease in N deposition, but critical deposition loads for nutrient N are exceeded in more than half of the monitoring plots in Europe (
Our results show that all evaluated soil horizons (humus layer and mineral soil up to 20 cm depth) are affected by high N input. This is an important confirmation that not only the soil surface is influenced. It clearly shows that forest soil is already saturated by N in some regions and that there is mid- or long-term influence of N compounds on forest soil. If the soil is N-saturated, there is a risk of high leaching of N compounds to the ground water. In the Czech Republic, the monitoring of runoff water in small forest catchments confirms this finding, as the concentration of nitrate is quite high (> 5 mg l-1) and related with high N deposition (
Moreover, the realistic nitrogen deposition in Czech forests is likely to be much higher than the modeled values used for our analysis. The N deposition is likely to be substantially underestimated not accounting for several important non-measured compounds, such as NH3 and HNO3 (g), and contribution of occult deposition, as recently shown by
There is a significant influence of N deposition on forest soil in the Czech Republic; between 1995 and 2006, concentration of total N increased in the upper 20 cm of soil. Deposition load exceeded the critical threshold for forest ecosystem in the Czech Republic. The results suggest that N deposition still represents a threat for forest ecosystems in the Czech Republic.
For their support we would like to thank the Ministry of Agriculture of the Czech Republic, Projects No. RO0114 (č.j. 8653/ 2014-MZE-17011) and No. QI112A168 (“Forest soil as the determining factor for forest health, biodiversity and the base for forest production, as well as for nonproductive functions”). We also highly appreciate the comments of three anonymous reviewers who substantially enhanced our manuscript. Last but not least we thank Sharon King for proofreading the paper.
Location of the plots (black dots) selected for the vegetation survey in the Czech Republic.
Box plots for selected parameters according to soil layer and year of soil survey.
Modeled deposition for the selected monitoring plots and years.
Basic characteristics of the plots assessed in both soil surveys (1995 and 2006) and chosen for comparison. The total number of plots was 66.
Parameter | Tree species / range of parameter | Number |
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Main tree species | Norway spruce | 46 |
Scots pine | 7 | |
European beech | 3 | |
clear cut between surveys | 10 | |
Age in 1995 | < 50 | 0 |
51-100 | 45 | |
>100 | 8 | |
not known | 13 | |
Age in 2006 | < 50 | 8 |
51-100 | 28 | |
>100 | 25 | |
not known | 5 | |
Altitude | < 400 m a. s. l. | 8 |
401-800 m a. s. l. | 49 | |
> 800 m a. s. l. | 9 |
Non-parametric test of difference in nitrogen concentration and C/N ratio in soil between plots with and without selected nitrophilous species.
Species | w/wo | Test | FH | M01 | M12 | |||
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Ntot | C/N | Ntot | C/N | Ntot | C/N | |||
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24/121 | KW | 0.205 | 0.000 | 0.074 | 0.000 | 0.007 | 0.000 |
MT | 0.192 | 0.000 | 0.168 | 0.000 | 0.023 | 0.000 | ||
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30/115 | KW | 0.622 | 0.006 | 0.571 | 0.001 | 0.238 | 0.001 |
MT | 0.966 | 0.045 | 0.388 | 0.045 | 0.203 | 0.000 | ||
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33/112 | KW | 0.320 | 0.045 | 0.233 | 0.001 | 0.233 | 0.000 |
MT | 0.345 | 0.033 | 0.152 | 0.001 | 0.523 | 0.000 | ||
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50/95 | KW | 0.693 | 0.000 | 0.011 | 0.000 | 0.001 | 0.002 |
MT | 0.772 | 0.000 | 0.012 | 0.000 | 0.000 | 0.001 |
Significance of differences in selected soil parameters between 1995 and 2006 after non-parametric pair tests. (ST): Sign test; (WPT): Wilcoxon pair test; (FH): humus layer; (M01): mineral soil (0-10 cm); (M12): mineral soil (10-20 cm).
Parameter | Horizon | n | ||
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ST | WPT | |||
pH (CaCl2) | FH | 65 | 0.000 | 0.000 |
M01 | 66 | 0.010 | 0.003 | |
M12 | 64 | 0.004 | 0.000 | |
pH (H2O) | FH | 65 | 0.000 | 0.000 |
M01 | 66 | 0.000 | 0.000 | |
M12 | 66 | 0.000 | 0.000 | |
carbon | FH | 66 | 0.036 | 0.006 |
M01 | 66 | 0.000 | 0.000 | |
M12 | 66 | 0.000 | 0.000 | |
nitrogen | FH | 66 | 0.176 | 0.072 |
M01 | 66 | 0.000 | 0.000 | |
M12 | 66 | 0.000 | 0.000 | |
C/N ratio | FH | 66 | 0.110 | 0.047 |
M01 | 66 | 0.005 | 0.060 | |
M12 | 66 | 0.110 | 0.015 |
Significance of differences in total nitrogen deposition and total H+ ions deposition between 1995, 2004 and 2006 after non-parametric pair tests. (ST): Sign test; (WPT): Wilcoxon pair test; (N): total nitrogen deposition; (H+): total acid deposition.
Pair Comparison | ||
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ST | WPT | |
N 1995 - N 2004 | 0.000 | 0.000 |
N 1995 - N 2006 | 0.000 | 0.000 |
N 2004 - N 2006 | 0.065 | 0.121 |
H+ 1995 - H+ 2004 | 0.000 | 0.000 |
H+ 1995 - H+ 2006 | 0.000 | 0.000 |
H+ 2004 - H+ 2006 | 0.000 | 0.000 |
Correlation between total nitrogen deposition and total H+ ions deposition and selected soil parameters. For each parameter/horizon combination, the
Parameter(1995/2006) | Horizon | Total nitrogen deposition | Total acid deposition | ||||||||||
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1995 (n=66) |
2004 (n=66) |
2006 (n=66) |
1995 (n=65) |
2004 (n=66) |
2006 (n=66) |
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S-R | K-T | S-R | K-T | S-R | K-T | S-R | K-T | S-R | K-T | S-R | K-T | ||
pH (CaCl2) | FH |
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-0.25 | -0.18 | -0.06 | -0.06 | 0.13 | 0.09 | -0.14 | -0.10 | 0.02 | 0.02 | 0.20 | 0.14 | ||
M01 |
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-0.29 | -0.20 | -0.03 | -0.02 | 0.08 | 0.04 | -0.25 | -0.17 | -0.04 | -0.04 | 0.09 | 0.06 | ||
M12 |
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-0.12 | -0.08 | 0.00 | -0.01 | 0.10 | 0.06 | -0.18 | -0.14 | -0.11 | -0.07 | 0.01 | 0.01 | ||
pH (H2O) | FH |
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-0.30 | -0.23 | -0.07 | -0.05 | 0.03 | 0.02 | -0.20 | -0.13 | 0.00 | 0.00 | 0.06 | 0.04 | ||
M01 |
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-0.32 | -0.23 | -0.06 | -0.05 | 0.07 | 0.04 | -0.24 | -0.17 | -0.06 | -0.03 | 0.07 | 0.04 | ||
M12 |
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-0.19 | -0.14 | -0.10 | -0.07 | 0.04 | 0.02 | -0.19 | -0.14 | -0.16 | -0.10 | -0.05 | -0.03 | ||
Nitrogen | FH |
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-0.12 | -0.07 | 0.24 | 0.17 | 0.07 | 0.05 | -0.14 | -0.10 | 0.04 | 0.02 | -0.12 | -0.09 | ||
M01 |
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0.35 | 0.24 | 0.23 | 0.16 | 0.18 | 0.12 | 0.13 | 0.08 | 0.00 | 0.00 | -0.05 | -0.03 | ||
M12 |
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0.22 | 0.16 | 0.27 | 0.17 | 0.21 | 0.15 | 0.11 | 0.08 | 0.01 | 0.01 | -0.02 | 0.00 | ||
C/N ratio | FH |
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0.13 | 0.08 | -0.50 | -0.35 | -0.44 | -0.32 | 0.00 | 0.00 | -0.38 | -0.26 | -0.22 | -0.15 | ||
M01 |
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0.05 | 0.04 | -0.26 | -0.16 | -0.24 | -0..16 | 0.11 | 0.09 | -0.28 | -0.19 | -0.18 | -0.12 | ||
M12 |
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0.03 | 0.03 | -0.07 | -0.04 | -0.15 | -0.11 | 0.07 | 0.04 | -0.11 | -0.08 | -0.12 | -0.08 |