Augustaitis, A., Šopauskienė, D. and Baužienė, I. 2010. Direct and Indirect Effects of Regional Air Pollution on Tree Crown Defoliation.  Baltic Forestry 16 (1): 23-34

Changes in tree crown condition, in most cases, may be related to the integrated impact of natural and anthropogenic factors, where S and N deposition, through the combination of direct, above-ground, impacts of SO₂, NO_x and NH₄+ on foliage and indirect, soil-mediated, impacts on roots play a predisposing, accompanying and locally, even a triggering role. This study was designed to check which effect is more significant on changes in tree crown defoliation. The findings revealed that the direct effect of air pollutants and acid deposition should be a more significant on Scots pine crown defoliation than the indirect effects of acidifying compounds through soil, ground and runoff water. Needles, which are present on trees all year round, seem to be more efficient aerosol collectors than leaves. In contrast, the direct effect of the considered contaminators, especially N compounds, on birch defoliation, was less pronounced than their indirect effect. In most cases, the considered contaminators had a negative effect on crown condition; meanwhile nitrate, its deposition and concentration in soil and groundwater, had a positive effect. Ips typographus L., which caused the dying of spruce trees, did not allow fulfilling the task.

Key words: nitrogen and sulphur deposition, soil and ground water contamination, tree defoliation.