Storage and redistribution of water in the forest floor influence evaporation, retention and infiltration patterns

The forest floor (FF) possesses significant water retention capacity, facilitating the transfer of water between the atmosphere and the soil. However, knowledge on the water retention characteristics and water transport effects of the FF remains limited. Due to the predominance of laboratory investigations regarding the storage capacity of a forest’s litter layer, we designed and constructed a new grid lysimeter to directly and in-situ measure the water fluxes from and into the FF. The objective was to ascertain further information regarding storage capacities, retention durations, and resulting infiltration patterns.

We present the results of a network comprising forest floor lysimeters and soil moisture probes at three sites with different altitudes located in the Black Forest, SW Germany. The three sites exhibit an annual mean temperature gradient from 6.3°C to 10.3 °C, leading to humus forms that vary from typical F-Mull to typical Moder according to KA6. We analyze water fluxes in relation to two distinct tree species (beech and spruce) and varying positions under the tree crown (middle and edge).

Throughout the monitored period in 2024, we determined that water was retained up to six days in the FF, while the amount of stored water was higher in Moder compared to the F-Mull. Our innovative gridded lysimeter design enabled us to demonstrate the small-scale (0.0625 m²) variety of spatio-temporal infiltration patterns, which is significantly influenced by the FF. The findings of our lysimeter network provide a comprehensive understanding of the influence of the forest floor on the water cycle within forest ecosystems.