In recent years the atmospheric deposition patterns of sulphur, nitrogen and heavy metals have changed dramatically in 'the industrial world'. The emissions of sulphur and heavy metals have decreased, whereas the emissions of nitrogen compounds have increased to a smaller or larger extent. In parallel, changes in land use and management practice have contributed to changes in the cycling of elements and in soil conditions. Afforestation and deforestation can also change atmospheric dry deposition and the processes controlling the mobility of nutrients and acidifying substances. Different types of forest management such as choice of tree species, deforestation by clear-felling or selection forest, fertilization, liming, sludge and compost addition, etc. will influence the leaching of nutrients from forest ecosystems. Since nitrogen is assumed to be the most important macronutrient in European forest, its input, cycling, turnover, and possible leaching is of crucial interest for forest management. The input of oxidised forms of nitrogen, together with sulphur, contributes to acidification of forest soils, but internal transformation processes, like nitrification, also contribute to acidification of soils. The critical load for atmospheric deposition of nitrogen can be evaluated in relation to nitrogen saturation, leaching, afforestation/deforestation, stand history and environmental conditions. In such assessments the chemical forms of nitrogen, spatial variability and time resolutions for turnover processes should be considered in combination with the input-output of other elements, especially sulphur. (C) 1998 Elsevier Science B.V.