ATMOSPHERIC DEPOSITION AND IMPACT OF FOREST THINNING ON THE THROUGHFALL OF MOUNTAIN FOREST ECOSYSTEMS IN THE BAVARIAN ALPS

The input into two forested watersheds in the Bavarian Alps is charact erised by 2000 mm mean annual precipitation. Evaporation from the tree crown surfaces varies between 25 and 30%. The input is influenced by multiple natural and man-made processes. In addition to the general cl imate, these are local weather conditions, the growing season, process es of combustion (traffic and domestic fuel), tourism, farming, and no t least by processes in the canopy. The input of SO4-S is comparativel y low, while high amounts of acidity and nitrogen are deposited. The i nput occurs mainly as dissolved salts. A considerable amount of the ac idity deposited is buffered in the canopy by cation exchange and by ca lcareous dusts, which are blown out from the limestone and dolomite mo untains nearby and redeposited on leaf surfaces. Forest thinning (remo val of 40% of the stem volume) caused marked changes in the deposition pattern. Interception and deposition rates of individual ions were re duced by up to 45%. The amount and chemical composition of the through fall occupied an intermediate position between bulk precipitation and the throughfall of the control watershed. Ions which are preferentiall y exchanged and leached from the leaves, e.g. potassium and organic co mpounds, were affected the most. (C) 1997 Elsevier Science B.V.