The influence of excessive precipitation on chemical changes in forest soils

The analysis of chemical changes in forest soils is based on Lithuanian forest monitoring data for 1992 and 1998. Precipitation in June-August 1998 averaged 2-5 times greater than in the respective months of 1992. Due to excessive precipitation in 1998 no changes were detected in total nitrogen content in forest litter and the mineral topsoil layer (0-20 cm) of Arenosols and Luvisols in Scots pine and Norway spruce stands (32 permanent observation plots). The acidity of forest litter and the upper mineral layer neither increased nor became significantly more alkaline. This could be explained by the migration of basic exchangeable cations from deeper, more alkaline horizons with ground water or through capillaries. However, organic carbon concentrations, which reflect the state of the humus, decreased in the mineral topsoil layer by 1.6-2.1 times. The paper concludes that abnormally intensive precipitation could have both positive and negative effect on the condition of forest soils in Lithuania.