Drifting dunes in the Curonian Spit of western Lithuania were covered by native Pinus sylvestris and alien Pinus mugo species. With planting of non-native species there is a need for studies which could evaluate the effect of alien and native plant species on soil ecosystem properties. We measured soil fungi amount, microbial enzyme activity, needle decomposition rate, respiration intensity, and soil and needle chemical composition from nearby pairs of native and alien pine species at different ages from several sites on the dunes (Lithuania). A total of 18 sampling sites of close-growing P. sylvestris and P. mugo were selected with stand ages ranging from 14 to 120 years, representing three age classes. Needles of P. sylvestris showed a faster decomposition rate than P. mugo. Needles of P. mugo had lower nitrogen content, higher C/N ratio and lignin content compared to P. sylvestris. The mass loss of needle litter was also positively correlated with C/N ratio and with fungi abundance in soil. Soil under Pinus sylvestris has higher C and N concentration than under P. mugo. The tendencies showed that there were more fungi in the soil under P. sylvestris than under P. mugo. Soil enzyme activity was lower in the P. mugo plots. The activities of invertase, dehydrogenase, alcaline phosphatase, protease, potential nitrification activity increased gradually with the development of forests after afforestation. These results suggest that due to the differences in litter properties and decomposition rates, changes may occur in microbial properties and nutrient cycling in the forest ecosystems.

Key words: litter decomposition, enzyme activity, Scots pine, mountain pine, litter quality.