Seasonal dynamics of tree species specific soil moisture patterns

Abstract:

Soil moisture patterns in the landscape are largely controlled by soil types (pore size distributions), landscape position and precipitation events. But how strong is the influence of vegetation on patterns within a single soil type? While we would envision a clear difference in soil moisture patterns and responses between for example bare soil, a pasture and a forest, our conceptual images start to become less clear when we compare different forest stands. Do different tree species cause species specific moisture patterns to emerge? Do these patterns change with the seasons? To investigate this question we analyzed data from 15 sensor clusters in the lowlands of north-eastern Germany (within the TERENO observatory) which were instrumented with soil moisture sensors (5 profiles per site), tensiometers, sap flow sensors, throughfall and stemflow gauges. Data has been collected at these sites since May 2014. While the soils under beech trees were more often relatively wet and more often relatively dry, the soils under pine trees showed less variability and more often average soil moisture. These differences could be explained by differences in the complex interactions between throughfall and stemflow on the one hand as well as root water uptake and sap flow patterns on the other hand. Further analysis will explore hydraulic redistribution between soil layers and hydraulic lift of groundwater (using root zone water balance methods and stable water isotope samples that were taken at different depths in the soil, in the groundwater and from the sapwood). The manifestation of tree species differences in soil moisture patterns and dynamics is likely to have implications for groundwater recharge, transit times and hydrologic partitioning within the critical zone.