The condition of forests in Europe.

Of the 42 countries participating in ICP Forests, 29 countries reported for the year 2011 largescale (Level I) monitoring data from about 15,000 plots and forest ecosystem related (Level II) monitoring data from about 700 plots. The data analysis focused on the impact of air pollution on forest soils, tree nutrition, and tree crown condition. In this respect emphasis was laid on the assessment of future risks of air pollution damage to the forests in Europe. Also considered was the impact of factors other than air pollution such as pests and diseases. Mean annual throughfall and bulk deposition of S and N was calculated for 289 and 357 Level II plots, respectively. S deposition is highest in central Europe, ranging from the North Sea coast via central Germany to Poland, the Czech Republic, and the Slovak Republic. High S deposition along the coast mostly occurs with high Cl deposition indicating that S deposition originates from sea salt. The fact that throughfall is higher than bulk deposition confirms that the canopy filters sulphur from the air. Similar to S deposition, N deposition is highest in central Europe but extends further west to France, the United Kingdom, and Ireland, as well as further south to Switzerland. On about half of the investigated sites there is a statistically significant decrease in S and N deposition between 2000 and 2010. For assessing effects of N deposition on the nutrition of trees, the exceedances of harmful pollutant concentrations (critical limits) in the soil were calculated. Up to 251 Level II plots were included in the study depending on data availability. Deposition data included throughfall and bulk deposition. Soil solution was sampled using lysimeters in the same intervals as deposition. For different soil depths annual mean concentrations and their exceedances of critical limits published in the scientific literature were assessed. Results show a clear relation between N deposition and the occurrence of high nitrate concentrations below the rooting zone indicating N saturation at the particular sites. Nutrient imbalances related to high nitrate concentrations could be substantiated. Mg deficiencies occur more frequently on coniferous plots with exceedances of critical limits for nitrate in the soil solution. Also for beech trees the percentage of plots with low Mg amounts is higher on plots with critical limit exceedances. For spruce, pine, beech and oak there is a tendency towards less optimal Mg/N ratios with increasing exceedances of critical limits for nitrate in the soil solution. The share of trees with light green to yellow discoloration is higher when critical limits for nutrient imbalances are exceeded. The share of trees showing insect damage is related to the exceedance of critical levels for the BC/Al ratio. Crown condition is the most widely applied indicator for forest health and vitality in Europe. Mean defoliation of 135,388 sample trees on 6,807 transnational Level I plots was 19.5%. Of all trees assessed a share of 20.0% was scored as damaged, i. e. had a defoliation of more than 25%. Of the main species groups, deciduous temperate oak species had by far the highest mean defoliation (24.4%), followed by deciduous Sub-Mediterranean oak species (22.0%), and evergreen oak species (21.2%). A mean defoliation of 20.7% was assessed for Fagus sylvatica. Coniferous species had lower defoliation, with Mediterranean lowland pine species showing 20.4%, followed by Picea abies (18.6%), Pinus sylvestris (18.1%). These figures are not comparable to those of previous reports because of fluctuations in the plot sample, mainly due to changes in the participation of countries. Therefore, the long-term development of defoliation was calculated from the monitoring results of those countries which have been submitting data since 1992 every year without interruption. While defoliation of Scots pine and 8 Forest Condition in Europe 2012 Norway spruce decreased, defoliation of Fagus sylvatica and the oak species groups increased since 1992. In addition to defoliation, crown condition assessments comprise discoloration as well as damage caused by biotic and abiotic factors. Among the different damage factors, insects and fungi are the most frequent ones.