Investigation results so far have shown that pollution has a serious negative effect on the forest ecosystems in Croatia. With regard to the air pollutants most research has been directed to the damaging effect of SO2 and products of its conversion. NOx, O3 and fluorides have been less investigated. SO2 has particular importance for Croatia because domestic coal contains a lot of sulphur, and the industrial plants which use it do not have devices for desulphurization. Furthermore, considerable amounts of sulphur arive by way or "distant transportation" from other countries. In this respect western cyclonic activities have special importance. As the regions of East Istria and Rijeka-Bakar industriel zone incorporate a number of large industrial plants which use coal (thermo-electric power plant, oil refinery, coke, plant, etc.) the vegetation of East Istria, Rijeka-Bakar area and the forests in Gorski kotar are exposed to the severe damaging effect of SO2. In the vicinity of the above sources, as well as in the areas of big towns (Zagreb, Karlovac, etc.) SO2 has a direct effect on vegetation. Besides other consequences, it is reflected also in high S-concentrations in assimilation organs. At some distances from the SO2 source sulphur is first deposited in dry depositions of sulphur, followed by damp depositions, while the remaining smaller part is transported to more distant places. In this, rather large area the indirect effect of SO2 on ecosystems becomes fully visible, which is especially manifested in a "new kind" of forest deterioration. The conversion of SO2 into other compounts and their deposition results in a decrease of sulphur concentrations in leaves, or needles of coniferous trees in the area of the Kvarner Bay and Gorski kotar and further, but in increases the frequency of acid rains. In Gorski kotar, where the largest zone of the fir-tree, our most severly damaged tree, is located, the total S-deposits amount to approximately 4 t S/km2 annually. By using the micro-habitat method the presence of emissional acidification of forest soils was determined in almost the whole of Croatia. This process has been particularly pronounced in West Croatia. The same is applicable to the loading of our forest ecosystems by lead and other heavy metals. In West Croatia the stands in the south-western aspects and on higher altitudes are most exposed, and in East Croatia the stands on the southern aspects and rifges of Slavonian mountain range, are most exposed. High concentrations of lead and zink have been determined in the surroundings of the thermo- electric power plant Plomin and beside roads. However, the largest amounts of heavy metals are introduced into the soil of lowland forests by polluted flood water. Extreme values were determined on the inundation terrains of the Varazdin region, and also in the lower stream of the Drava river, .....
