NITROGEN-INDUCED NUTRITIONAL IMBALANCES - A CONTRIBUTING FACTOR TO NORWAY SPRUCE DECLINE IN THE BOHEMIAN FOREST (AUSTRIA)

Studies of forest-decline symptoms in the Bohemian Forest of Austria showed significant effects of topography on forest conditions. Needle loss, as a measure of the tree vigour, was more severe in higher elevations and on west slopes which face the prevailing winds. Drought periods seem to enhance needle loss on temporarily waterlogged sites. Nutritional imbalances, especially low magnesium and calcium contents in the foliage and wide nitrogen-to-magnesium ratios were correlated with increased needle loss. Measurements of element fluxes at ground level have shown that nitrogen flux with throughfall was 30-70% higher and sulphur flux about 50% higher on a southwest slope and hilltop as compared with a northeast slope. Deposition rates in the open did not differ significantly between sites. Cloud- and fogwater deposition was the main source of higher inputs at the exposed sites. On the southwest slope, nitrogen losses via seepage were of the same magnitude as gains from atmospheric deposition, an indication of nitrogen saturation. On the northeast slope, nitrogen inputs could still be stored in soil and vegetation. This study shows that pollutant deposition, in particular nitrogen deposition, exceeds the buffering capacity of forest ecosystems on shallow, acidic soils of exposed west slopes. This leads to nutritional imbalances.