Stemflow Infiltration Research Articles

Routing stemflow water through the soil via preferential flow: a dual-labelling approach with artificial tracers

Abstract. Stemflow and its belowground funnelling along roots and macropores may play an important role in the soil moisture redistribution in forest environments. In this study, a stemflow experiment on Pinus sylvestris L. (Scots pine) used artificial tracers to view and quantify preferential flow after stemflow infiltration into the soil. A total of 41 L of water labelled with enriched deuterium and brilliant blue FCF were applied at a flow rate of 7 L h−1 to the stem of a pine tree, which corresponds to the stemflow caused by about 50 mm of rainfall. Time domain reflectometry (TDR) probes were installed around the tree trunk to measure the high-resolution volumetric water content. A total of 1 d after the stemflow discharge, soil pits were dug in the different cardinal directions and at varying distances from the tree. Photographs were taken for imaging analysis to quantify preferential flow metrics. Soil samples were taken from the different profiles to analyse the dye concentrations and isotopic compositions. We found that stemflow infiltrated through an annulus-shaped area around the tree base. We observed a heterogenous spatiotemporal soil moisture response to stemflow and the occurrence of shallow perched water tables around the tree trunk. Dye staining demonstrated that stemflow infiltrated primarily along the surface of coarse roots and through macropores. The dye coverage was less extensive close to the soil surface and increased with depth and with proximity to the tree trunk. Lateral flow was also observed, mainly in the shallow soil layers. Our analyses demonstrate the prevalence of preferential flow. Deuterium and brilliant blue FCF concentrations were significantly correlated. The tracer concentrations decreased with increasing distance from the tree trunk, indicating dilution and mixing with residual soil water. Macropores, coarse roots (living or decayed) and perched water tables produced a complex network regulating the preferential flow. Our results suggest that stemflow affects soil moisture distribution, and thus likely also groundwater recharge and surface runoff. Our study provides insights into the soil hydrological processes that are regulated by stemflow belowground funnelling and improves our understanding of forest–water interactions.

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

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.

Evaluating subsurface flow connectivity in a pine-covered hillslope with stemflow infiltration and ground-penetrating radar surveys

The hydrological response of sloping catchments is strongly conditioned by the connectivity of subsurface preferential flows. The objective of this paper is to investigate the role played by stemflow infiltration in subsurface water flow dynamics, focusing on a forested hillslope located in an Aleppo pine Mediterranean forest (Pinus halepensis, Mill.) located at Sierra Calderona, Valencia province, Spain. We combined stemflow artificial experiments with the ground-penetrating radar (GPR) as a non-invasive technique to investigate stemflow-induced preferential flow paths activated by different trees and the related hydrological connectivity at the hillslope scale. Our observations allowed us to identify different dynamics associated with the initiation of stemflow and then lateral preferential flow, including the activation of connected preferential flow paths that received stemflow water from different trees. These observations provided empirical evidence of the role of stemflow in the formation of lateral preferential flow networks. Our measurements also provided estimations for flow velocities, which provided new insight on the magnitude of stem-induced lateral preferential flow paths. The applied protocol offers a simple, repeatable and non-invasive way to conceptualize hillslope responses to rainstorms.

Stemflow infiltration areas into forest soils around American beech (Fagus grandifolia Ehrh.) trees

AbstractThe size of stemflow infiltration areas around the boles of trees is currently a topic of interest and debate within the hydrologic community. There is a gap in our knowledge of stemflow infiltration areas in many wooded ecosystems and a need for more than the few studies that have examined stemflow infiltration areas directly. Hence, this field study was specifically undertaken to mitigate the existing data gap by providing direct measurements of stemflow infiltration areas from high stemflow‐producing American beech (Fagus grandifolia Ehrh.) trees. Different stemflow rates (290, 72 and 31 L h−1) were simulated using dye‐infused stemflow and the areas of stemflow infiltration around four trees determined by measuring the areal extent of dye on the soil surface. Our results revealed that stemflow infiltration areas ranged from 0.0035 to 0.0951 m2 tree−1. The mean basal area funnelling ratio was 46.5 ± 1.8, whereas the funnelling ratios per unit infiltration areas, , were between 32.0 and 258.4. Despite intentionally high stemflow rates, chosen to compensate for the high infiltration capacities of forest soils, these results reinforce the fact that stemflow is an extremely localized input in natural forests. Thus, these results, even if specific to F. grandifolia within a particular forest and soil type, support a growing body of work indicating that stemflow infiltration areas are usually <1 m2, and often much smaller, in natural forests. Moreover, the high values of provide further evidence indicating that stemflow inputs are important for the development of hot spots in near‐trunk soils.

Stemflow Infiltration Hotspots Create Soil Microsites Near Tree Stems in an Unmanaged Mixed Beech Forest

In stemflow, rainfall is collected and channeled to a concentrated soil water input. It can constitute up to 30% of incident precipitation in some ecosystems. However, the size of the zone influenced by stemflow is unclear, and statistically representative measurement of stemflow (on and in between sites) is scarce. Therefore, whether stemflow creates hotspots of infiltration and potential impacts on forest soils remain subject to controversy. In this study, we investigated the areal dimension of infiltrating stemflow fluxes as well as effects on near-stem soils. We measured throughfall, stemflow and soil properties in high-resolution statistical designs on a mixed forest plot in Germany receiving moderate stemflow. From this data, we modeled the spatial distribution of net precipitation infiltration depth on the plot. Furthermore, we examined soil chemical and physical properties around tree stems to test for and assess a stemflow impact. Results show that stemflow infiltration areas are much smaller than typically assumed and constitute strong infiltration hotspots compared to throughfall. This is also mirrored in soil properties, which are significantly altered near stems. Here, accelerated soil formation and enhanced translocation processes indicate increased soil water fluxes due to high inputs. Additionally, altered soil hydraulic properties enable quicker soil water fluxes near stems. Our findings attest that even comparatively low stemflow fractions (of gross precipitation) can generate strong hotspots of water and matter inputs, which are impactful to subsequent hydrological and biogeochemical processes and properties. Trees shape their direct soil environment, thereby establishing pathways of preferential water flow connecting the canopy and the deeper subsurface.

Response: Commentary: What We Know About Stemflow's Infiltration Area

Response: Commentary: What We Know About Stemflow's Infiltration Area

Commentary: What We Know About Stemflow's Infiltration Area

This commentary was written in conjunction with Project LinkA20045 of the international scientific collaboration program i-LINK+ 2018 funded by the Spanish National Research Council (CSIC).

Nonuniform but highly preferential stemflow routing along bark surfaces and actual smaller infiltration areas than previously assumed: A case study on European beech (Fagus sylvatica L.) and sycamore maple (Acer pseudoplatanus L.).

AbstractCanopy and tree morphology are assumed to play a significant role in modulating the amount of rainfall water during its routing throughout the vegetation and the near‐surface Critical Zone. One crucial point of research addresses the spatial extent of stemflow (SF) infiltration, because its concentration over small areas at the trunk base appears to affect the magnitude and timing of water and solutes input to the soil and hence amplify biogeochemical cycling. By a Brilliant Blue tracer experiment, we examined the flow patterns of SF water along the trunk surface of two broadleaved tree species (Fagus sylvatica and Acer pseudoplatanus) and the infiltration area at the trunk base and down to 0.12‐m soil depth following natural rainfall events.Our results point to highly preferential SF with smaller washed‐off stem areas for sycamore maple (≤15%) compared with European beech (≤39%). The infiltration area is remarkably smaller than the basal area (BA), accounting for only 17% of the BA for beech and for 30% for maple. Differences in decolourized stem areas between the trees do not relate to the magnitude of infiltration areas at the soil surface, suggesting a strong effect of coarse root abundance and run‐off properties on the funnelling of SF water.In essence, our investigation exhibited that SF routing along bark surfaces and infiltration at the trunk base were spatially more concentrated than commonly assumed. The outcome of this study might contribute to our understanding on hydrological and biogeochemical interlinkages between the plant cover and the near‐surface Critical Zone.

What We Know About Stemflow's Infiltration Area

A portion of precipitation drains to the surface down plant stems, as “stemflow.” Although, per observations to date, stemflow rarely represents >2% of gross precipitation in forests, it can result in larger water fluxes to near-stem soils that are hypothetically more important to roots. The ecohydrological importance of stemflow is often predicated upon assumptions about how it infiltrates into near-stem soils. Our objective is to review the small number of studies over the ~140 years of stemflow research that have quantified its infiltration area. We found several empirical descriptions of stemflow infiltration areas inferred from disparate approaches, and we discuss that evidence in the context of dominant assumptions and conceptualizations (i.e., equating infiltration area to basal area or estimations based on assumed soil conductivity metrics). However, we conclude that more empirical understanding of stemflow infiltration is needed before we quantify or qualify stemflow’s influence from its assumed infiltration rate. Towards this goal, we provide a critical discussion of two methods that seem most promising for quantifying stemflow infiltration area.

Pairing geophysical techniques improves understanding of the near-surface Critical Zone: Visualization of preferential routing of stemflow along coarse roots

There is compelling evidence from aboveground observations that trees considerably affect precipitation partitioning through the Critical Zone. However, due to the lack of appropriate methods, the role of root systems (the hidden half of trees) on redistributing precipitation and infiltration into and routing through the soil remains inadequately visualized and understood. Here, we designed a novel experiment to pair two non-invasive geophysical techniques, ground-penetrating radar (GPR) and electrical resistivity tomography (ERT), to trace stemflow through the soil in a forested hillslope after water was released on the trunk of an American beech (Fagus grandifolia Ehrh.) to induce stemflow. We used GPR to locate lateral coarse roots and GPR and ERT together to confirm the wetting areas in response to the non-uniform transport of stemflow. Signal changes between time-lapse geophysical images were used to reveal both the response time and location of stemflow infiltration into and redistribution through the soil. This first known study to investigate the subsurface routing of stemflow by combining GPR and ERT revealed that the belowground funneling of stemflow along laterally oriented coarse roots transported water 2.8 m downslope from the study tree in 30 min after stemflow was initiated. In situ excavation validated the distribution of lateral roots and lateral root-derived preferential flow paths identified in geophysical images, confirming the utility of pairing GPR and ERT to gain insights into the temporal dynamics and spatial distribution of subsurface routing of stemflow. The proposed method visualized and confirmed the funneling effect of roots on belowground water redistribution that contributed to subsurface lateral flow. Pairing GPR and ERT provides a useful combination of geophysical methods to advance our understanding of the complex interactions between plant and soil, such as the role of tree roots in soil hydrological process by revealing areas of funneling in the hidden part of the Critical Zone.

Soil water repellency and chemical soil properties in a beech forest soil — Spatial variability and interrelations

Higher solute input due to stemflow infiltration causes enhanced soil acidification near the tree base. Infiltration-driven alteration of chemical soil properties like pH, and carbon to nitrogen ratio (C/N) and particle surface properties like oxygen to carbon ratio (O/C), may also affect soil wettability with a trend to increased soil water repellency (SWR) with increased acidity. Our study provides a link between chemical soil quality and physical behavior with respect to soil water infiltration and SWR, respectively in a beech forest soil.The spatial variability of soil properties was analyzed within a grid (Δ=1m, 5m×8m=40m2) and, to reveal direct effects of stemflow influence on soil properties, we sampled along a tree row (Δz=0.8m, l=46.60m) with varying sampling points to tree distances. All samples were taken in a beech (Fagus sylvatica L.) forest Bws/Bw-horizon in 0.1–0.2m depth (dystric cambisol).Analysis of spatial variability by standard statistics and geostatistical methods revealed no substantial differences between grid and transect samples for pH and sulfate, Al, and Fe (aluminum and iron oxalic acid extractable) concentration and SWR in terms of contact angle (CA, sessile drop method) measured for bulk soil samples. According to standard statistics, the total variance of chemical soil properties and SWR was independent of stemflow infiltration pattern. Results of spectral variance analysis showed that the spatial variability of acidification (pH, Al content) as well as SWR was strongly affected by the pattern of patches with and without stemflow infiltration or the distribution of beech trees, respectively. In a more or less regularly planted beech forest this caused a cyclic variation of soil acidification and SWR with a strong trend to increased SWR (CA ranges 17°–72°) with increased soil acidity. Specific chemical surface properties, analyzed via X-ray photoelectron spectroscopy, like O/C ratio (r2=0.782) and the amount of nonpolar C species (r2=0.768) as well as surface Al concentration (r2=0.867) clearly showed a strong relation to CAs. Hence, SWR was strongly affected by stemflow infiltration patterns into soil. For C/N, sulfate, and Fe content no significant relations to SWR or soil acidity were found.

Edaphic heterogeneity related to below-canopy water and solute fluxes in a Canarian laurel forest

Aim To study the differences in the edaphic properties between stemflow infiltration areas around different tree species and between these and other areas of the forest.

Evidence of double-funneling effect of beech trees by visualization of flow pathways using dye tracer

Summary The aim of this study was to determine how the crown and root architecture of beech trees control stemflow formation, stemflow infiltration, and the subsurface transport of stemflow through the soil with a novel dye tracer experiment. With this approach, it is possible to apply the dye solution directly to the stem, enabling a more advanced technique to represent the flow processes than has been used in previous studies. Stemflow concentrates and channels water over localized circular areas at the tree base, as shown in this study. Tracing stemflow using dye demonstrated that infiltrating stemflow water was preferentially funneled belowground along heart and sinker roots, laterally oriented coarse roots, and congregations of fine roots grown into decayed root channels of felled trees. The results presented in this study reveal that stemflow and root induced preferential flow triggers fast lateral subsurface flow bypassing large parts of the soil matrix at least during rainstorm events. Based on our measurements, we hypothesize that the formation of stemflow and the channeling of infiltrating stemflow water along the roots of beech trees might be an important mechanism of runoff generation in forested catchments.

Stemflow variation in Mexico’s northeastern forest communities: Its contribution to soil moisture content and aquifer recharge

► A comprehensive stemflow dataset was collected for two Mexico’s northern plant communities. ► For each species and for each stand, stemflow coefficients and infiltration depths are reported. ► Statistical stemflow differences are found between the species, plant communities and stands. ► Stemflow extrapolated threefold from trees to stands because of overstocked forests. ► Temperate forest stemflow appears to contribute to aquifer recharge because of shallow soils. Stemflow hydro-ecological importance was measured in trees and assessed in Mexico’s northeast forest stands by answering three basic questions: (a) what are the intra and inter-specific stemflow variations; (b) is the stemflow coefficient constant from tree level to stand scales? and (c) what is the stemflow area and wetted soil volume in individual trees and the stemflow volume discharged at the stand scale in two plant communities of northeastern Mexico? Gross rainfall and stemflow flux measurements were conducted on 78 trees of semi-arid, sub-tropical (31 Diospyros texana ; 14 Acacia rigidula ; four Bumelia celastrina ; five Condalia hookeri ; three Cordia bioissieri ; three Pithecellobium pallens ) and temperate forest communities (six Pinus pseudostrobus Lindl. and 12 Quercus spp.). Stemflow was extrapolated from individual trees to the stand scale using 98 inventory plots (1600 m 2 ha −1 each) placed in oak–pine forests and 37 quadrats (5 m × 5 m each) distributed across the Tamaulipan thornscrub forest range. Stemflow infiltration flux and infiltration area measurements assessed the wetted soil volume. Daily measurements were conducted from May of 1997 to November of 1998. Results showed that stemflow coefficients varied between plant communities since they averaged (confidence intervals, α = 0.05) 2.49% (0.57), 0.30% (0.09), and 0.77% (0.27) of the bulk precipitation for Tamaulipan thornscrub, pine, and oak forests, respectively. Intra-specific stemflow variations could not be identified in Tamaulipan although in temperate tree species. Basal diameter explained intra-specific stemflow variation in both plant communities. Stemflow increased threefold since it accounted for by 6.38% and 2.19% of the total bulk rainfall for Tamaulipan thornscrub quadrats and temperate oak–pine inventory plots, respectively. Small shrubs growing underneath large trees, in combination with the presence of small-diameter trees that recorded the largest stemflow coefficients appear to explain the increase of the stemflow coefficient from trees to stands. Stemflow replenishes soil moisture on the average 4.5 (1.4) times larger than does incident rainfall in open soils and appear to contribute to aquifer recharge in temperate forests due to a combination of shallow soils, high infiltration fluxes and the stemflow volume generated during rainfalls with depths >15 mm. Tracing studies should be conducted to test the hypothesis of the stemflow contribution to aquifer recharge in temperate forests of northeastern Mexico.

A three-dimensional model of the effect of stemflow on soil water dynamics around a tree on a hillslope

In forested stands, precipitation is intercepted by the canopy and partitioned into throughfall and stemflow as diffuse input and point input, respectively. Therefore, the water reaching the forest floor is not spatially uniform. Although there are many numerical models that simulate precipitation redistribution processes, the rainwater concentrated by stemflow is usually disregarded. In this study, we performed detailed observations of soil water dynamics during a storm event and developed a three-dimensional model of the effect of stemflow on soil water dynamics around a tree on a forested hillslope. In the stemflow infiltration process, water flowed rapidly through a deep layer, causing irregular changes in the vertical soil water content. This process is very different from the vertical rainfall infiltration process, in which the wetting front expands slowly from the upper layer to the deeper layer. Thus, simulations using the conventional net precipitation input assumption are likely to contain large errors as a result. The model proposed in this study, which considered the point input characteristic of stemflow and parameterized stemflow as a source flux spring in the soil layers, showed adequate spatial and temporal variations in soil water dynamics and closely agreed with observations. Applying the variable source term in the Richards equation to stemflow is a new approach and makes it possible to represent the root-induced bypass flow infiltration process around a tree growing on a hillslope.

Water and nutrient fluxes in a cool temperate rainforest at the Cordillera de la Costa in southern Chile

Water and nutrient fluxes were studied during a 12-month period in an alerce (Fitzroya cupressoides) forest, located in a remote site at the Cordillera de la Costa (40°05'S) in southern Chile. Measurements of precipitation, throughfall, stemflow, effective precipitation, soil infiltration and stream flow were carried out in an experimental, small watershed. Simultaneously, monthly water samples were collected to determine the concentrations and transport of organic-N, NO 3 -N, total-P, K + , Ca 2+ , Na + and Mg 2+ in all levels of forest Concentration of organic-N, NO 3 -N, total-P and K + showed a clear pattern of enrichment in the throughfall, stemflow, effective precipitation and soil infiltration. For Ca 2+ and Mg 2+ , enrichment was observed in the effective precipitation, soil infiltration and stream flow. Annual transport of K + , Na + , Ca 2+ and Mg 2+ showed that the amounts exported from the forest via stream flow (K + = 0.95, Na + = 32.44, Ca 2+ = 8.76 and Mg 2+ =7.16 kg ha -1 yr -1 ) are less than the inputs via precipitation (K + = 6.39, Na + =40.99, Ca 2+ =15.13 and Mg 2+ = 7.61 kg ha -1 yr -1 ). The amounts of organic-N and NO 3 -N exported via stream flow (organic-N=1.04 and No 3 -N=3.06 kg ha -1 yr -1 ) were relatively small; however, they represented greater amounts than the inputs via precipitation (organic-N = 0.74 and NO 3 -N = 0.97 kg ha -1 yr -1 ), because of the great contribution of this element in the superficial soil horizon, where the processes of decomposition of organic material, mineralization and immobilization of the nutrients occurs.

Analyzing field-measured soil-water properties

Higher solute input due to stemflow infiltration causes enhanced soil acidification near the tree base. Infiltration-driven alteration of chemical soil properties like pH, and carbon to nitrogen ratio (C/N) and particle surface properties like oxygen to carbon ratio (O/C), may also affect soil wettability with a trend to increased soil water repellency (SWR) with increased acidity. Our study provides a link between chemical soil quality and physical behavior with respect to soil water infiltration and SWR, respectively in a beech forest soil.The spatial variability of soil properties was analyzed within a grid (Δ = 1 m, 5 m × 8 m = 40 m2) and, to reveal direct effects of stemflow influence on soil properties, we sampled along a tree row (Δz = 0.8 m, l = 46.60 m) with varying sampling points to tree distances. All samples were taken in a beech (Fagus sylvatica L.) forest Bws/Bw-horizon in 0.1–0.2 m depth (dystric cambisol).Analysis of spatial variability by standard statistics and geostatistical methods revealed no substantial differences between grid and transect samples for pH and sulfate, Al, and Fe (aluminum and iron oxalic acid extractable) concentration and SWR in terms of contact angle (CA, sessile drop method) measured for bulk soil samples. According to standard statistics, the total variance of chemical soil properties and SWR was independent of stemflow infiltration pattern. Results of spectral variance analysis showed that the spatial variability of acidification (pH, Al content) as well as SWR was strongly affected by the pattern of patches with and without stemflow infiltration or the distribution of beech trees, respectively. In a more or less regularly planted beech forest this caused a cyclic variation of soil acidification and SWR with a strong trend to increased SWR (CA ranges 17°–72°) with increased soil acidity. Specific chemical surface properties, analyzed via X-ray photoelectron spectroscopy, like O/C ratio (r2 = 0.782) and the amount of nonpolar C species (r2 = 0.768) as well as surface Al concentration (r2 = 0.867) clearly showed a strong relation to CAs. Hence, SWR was strongly affected by stemflow infiltration patterns into soil. For C/N, sulfate, and Fe content no significant relations to SWR or soil acidity were found.