Monitoring forest condition in Europe: concentrations of nitrogen and sulphur in bulk deposition and defoliation of main tree species.

Forest condition in Europe has been monitored for 20 years jointly by the United Nations Economic Commission for Europe (UNECE) and the European Union (EU). Large-scale variations of forest condition over space and time in relation to natural and anthropogenic factors are assessed on about 6000 plots systematically spread across Europe. Causal relationships are studied in detail on about 860 intensive monitoring plots covering the most important forest ecosystems in Europe. This paper describes results of the large-scale defoliation survey, relationships between large-scale defoliation and modelled large-scale deposition, as well as of changes in concentrations of air pollutants in bulk deposition measured on intensive monitoring plots. There is an increase in defoliation of the most abundant species, with high spatial and temporal variation. Bulk deposition measurements indicate that sulphate and nitrate concentrations decreased from 1996 to 2001, whereas ammonium concentrations fluctuated during the same measuring period. [ABSTRACT FROM AUTHOR]