Litterbag studies on decomposition of Black alder, European beech, Norway maple and Red oak leaves were conducted in headwater riparian forest in northern Poland. Alder litter represent material produced in situ, whereas the remaing litters materials originating from external sources, supplied by wind. The highest intensity of decomposition was observed in rich in nitrogen alder leaves (k = 2.77 year^-1) and lower in maple (k = 1.02 year^-1), oak (k = 0.49 year^-1) and beech (k = 0.49 year^-1). In alder leaves, accumulation of N in the first phase of decomposition, and decrease in its concentration and stocks in the second phase were indicated. However, in leaves of remaining species accumulation of N over the whole experiment time was observed. Concentration of phosphorus in poor in the element alder leaves for all the time increased, and in richer maple, oak and beech leaves leaching in the first and accumulation in the second phase were observed. Potassium and magnesium were intensively leached during the first two months of decomposition from each litter, and in the next months their concentration was relatively stable, or increased. Release of calcium was related to weight loss of leaves, and its concentration was relatively stable over time. An intensive accumulation of iron and aluminium was observed in alder, maple and oak leaves, and much smaller in beech leaves. The observed differences among the litters in decomposition rate and nutrients release dynamics was strongly affected by chemical composition of initial materials. Especially large differences were observed among alder litter, as produced in situ, and the remaining litters originating from external sources. Based on the data obtained, we can conclude that beech, oak and maple litterfall influx from external sources can influence the intensity of accumulation, stocks and quality of soil organic matter in the investigated ecosystem.

Key words: litterfall decomposition, Black alder, European beech, Norway maple, Red oak, headwater areas