Atmospheric deposition at four forestry sites in the Alpine Region of Trentino- South Tyrol, Italy

The Trentino-South Tyrol Region is located in the southern part of the Alpine Chain. The territory is largely mountainous with crystalline rock formations dominant in the north and limestone in the south-east. Most of the land is open to the climatic and atmospheric influence of the River Po, via the mainly N-S oriented valley of the River Adige. The forestry authorities of the region have since the 80s been making an annual assessment of forest decline, particularly as regards parasite attacks, defoliation and crown discoloration, and have found the situation to be better than in most other parts of Europe. The region's forest protection policy is administered by the two provinces of Bolzano/Bozen and Trento in the framework of the European convention on Long Range Transboundary Air Pollution (UN-ECE LRTAP); each province operates two forestry sampling permanent plots. The sites are all constituted according to the standard recommendations, and are located in the central part of the region along the Adige Valley, where most of population live and where most of the agriculture and industry is. Two of the areas are in coniferous stands of the typical Alpine forest, mainly composed of Norway spruce; the other two are located in deciduous stands (both high forest and coppice) and are closer to the urban centres than the first two. Concentration and deposition values for the main ionic components in bulk, wet, throughfall, stemflow and soil water are given separately for the four monitoring sites, with reference to the period 1996- 1999. The major acidifying component in atmospheric precipitation is still sulphate, but as other investigations confirm, the relative importance of the nitrate input is increasing all the time. The effect of these changes is probably positive for terrestrial ecosystems in the short term because of the decrease in total acidifying input and the increase in inorganic fertilisation. The absence of major "forest" damage, outlined in the annual forest damage survey reports issued by the forestry authorities (internal reports since 1983), suggests that the current atmospheric acidic load is in balance with the stational and climatic conditions.