Bayreuther Institut für Terrestrische Ökosystemforschung
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Chang, S-C; Matzner, E: The effect of beech stemflow on spatial patterns of soil solution chemistry and seepage fluxes in a mixed beech/oak stand, Hydrological Processes, 14, 135-144 (2000)
Stemflow of beech (Fagus sylvatica L.) represents a significant input of water and elements to the soil and might influence the spatial patterns and the rate of seepage fluxes at the stand scale. We investigated the soil solution chemistry at different depths and distances from the stem and the element fluxes with stemflow, throughfall and seepage in proximal and distal stem areas of a 130-year-old beech/oak forest in Steigerwald (northern Bavaria, Germany). The proximal stem area (in total 286 m2ha-1) was defined as a 1m2, 60 cm deep cylinder around the beech stem. Seepage fluxes were calculated by a soil hydrological model for 1996 using measured soil matrix potentials and tree xylem flow data for calibration. Stemflow represented 6.6% of the annual soil water input. With the exception of H+ fluxes, less than 10% of the total element fluxes with throughfall and stemflow reached the soil via stemflow. The volume-weighted concentrations of H+, K+ and SO42- in stemflow were higher than those in throughfall, while other elements had similar concentrations. Soil solution K+ concentrations decreased with stem distance, but the Na+, Mg2+, CI- and SO42- concentrations increased. Gradients for other elements were not statistically significant. Stemflow had a strong influence on the spatial patterns of element fluxes with seepage. The water fluxes through the soil of the proximal stem areas at a depth of 60 cm contributed 13.5% to the total seepage at the stand scale. Proximal to the stems about 20% of total seepage for K+, Mn2+, Aln+, dissolved organic N and dissolved organic C were concentrated, but only 8-10% for Na+, Mg2+ and Ca2+. The loss of acid-neutralizing capacity calculated from the flux balance was about four times higher proximal to the stems compared with distal areas, indicating high rates of soil acidification proximal to the stems.
Our results confirm the concept of a microsite around beech stems, characterized by high element and water fluxes in comparison with distal stem areas. Calculations of seepage fluxes and element budgets in beech stands have to consider the spatial heterogeneity of fluxes induced by stemflow.
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