Abstract
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.
Highlights
Precipitation is redistributed by forest canopies into spatiotemporally heterogeneous patterns at the forest floor
Estimates of INFILTRATION AREAS (IT) have been made from various types of observations: post-storm litter marks caused by infiltration excess (Tanaka et al, 1991; Iida et al, 2005; Rashid and Askari, 2014); post-storm soil scour marks originating at the stem (Tanaka et al, 1991; Chinen, 2007); video recordings during storms (Cattan et al, 2009; Charlier et al, 2009; Keen et al, 2010); simulated stemflow during dry periods (Voigt, 1960; Schwärzel et al, 2012); in-storm measurement of the infiltration ring itself (Pressland, 1973, 1976; Gómez et al, 2002); dye tests (Spencer and van Meerveld, 2016; Imamura et al, 2017; Carlyle-Moses et al, 2018; Gonzalez-Ollauri et al, 2020); and estimates based on site-specific stemflow and near-stem infiltration rates
Some studies did not explicitly report IT due to observed significant runoff induced by stemflow. *Reported in Table 2 of Iida et al (2016). ‡Only the maximum infiltration area was estimated using distances measured with a meter tape from the downslope side of each tree bole to the furthest visible extent of the stain in the downslope direction (127 cm for study tree #1 and 63 cm for study tree #2 per with the study’s corresponding author). †Maximum stemflow IT estimated from data in paper and maximum distance of stain from the stem base provided by Gonzalez-Ollauri via personal communication
Summary
Precipitation is redistributed by forest canopies into spatiotemporally heterogeneous patterns at the forest floor This redistribution, is not always random and can involve the routing of water to specific places: notably, large canopy areas can capture and drain precipitation to the tree stem and down to nearby soils as stemflow (Tanaka et al, 1996; Metzger et al, 2019). This stemflow generation is highly variable across forest species and storm characteristics, but rarely exceeds 2% of the precipitation inputs to a forest (Carlyle-Moses et al, 2018; Van Stan and Gordon, 2018).
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