Stemflow infiltration hotspots near-tree stems along a soil depth gradient in a mixed oak–beech forest

Abstract

In an upland forested micro-catchment during the growing season, we tested soil responses to precipitation events as well as soil water content (SWC). We asked ourselves if what is the difference of SWC response to precipitation events depending on the presence and proximity of a tree? The environmental heterogeneity of the small 7.5-ha headwater area was captured by soil probes at specific locations: (i) probe measurements of SWC at 10-, 30-, 60-, and 100-cm depths; (ii) resolution of near-tree (NT) and between-tree (BT) positions; and (iii) resolution of four slope classes. The results revealed significant differences between the hydrological responses of the soil. NT soils had faster infiltration but were also faster to dry out when compared to BT soils, which were less affected by the presence of trees. Water input threshold values, measured as the precipitation amount needed to cause a significant increase in SWC, were also significantly different, with NT positions always lower than BT positions. Total infiltration of the topmost NT and BT soil layers reached 185 and 156 mm during the study period, corresponding to 43% and 36% of the total 434 mm of precipitation, respectively. Infiltration into the deepest horizon was significantly higher in NT soils, where it reached 114 mm (26%) as opposed to 9 mm (2%) in BT soils, and was indicative of significant vertical hydraulic bypass flow in the proximity of trees. These observations contribute to better understanding the hydrological processes, their nonlinearity, and the expansion of conceptual hydrological models.

Three Fundamental Challenges to the Advancement of Stemflow Research and Its Integration into Natural Science

“…In natural forest settings, preferential infiltration of stemflow along coarse roots and macropores has been documented using geophysical methods, like ground-penetrating radar and electrical resistivity tomography [71,72], high-resolution spatiotemporal monitoring via soil volumetric water content probes [73,74], tracing dyes [73,75,76], and a combination of these approaches [71,73]. Even in agriculture, such as with potatoes, similar deep infiltration patterns have been observed [4].…”

Tree trait-mediated differences in soil moisture regimes: a comparative study of beech, spruce, and larch in a drought-prone area of Central Europe

“…Since precipitation partitioning plays a fundamental role in regulating the input of water into the soil (Crockford and Richardson 2000), the after-rain distribution of soil moisture can vary spatially, depending on the distinctive structural characteristics of tree species. For example, the upward branch inclination and smooth bark of beech and oak trees promote enhanced stem ow, leading to the formation of in ltration hotspots near the tree base (Hemr et al 2023); in contrast, the downwards inclination of spruce branches results in dripping water at tree canopy line (Levia and Frost 2006;Levia and Germer 2015). A signi cant part of the precipitation is intercepted on the surface of vegetation, reducing the throughfall of precipitation and soil water recharge.…”