Commentary: What We Know About Stemflow's Infiltration Area

Carlyle-Moses, Darryl E.; Iida, Shin'ichi; Germer, Sonja; Llorens, Pilar; Michalzik, Beate; Nanko, Kazuki; Tanaka, Tadashi; Tischer, Alexander; Levia, Delphis F.

doi:10.3389/ffgc.2020.577247

GENERAL COMMENTARY article

Front. For. Glob. Change, 30 September 2020

Sec. Forest Hydrology

Volume 3 - 2020 | https://doi.org/10.3389/ffgc.2020.577247

Commentary: What We Know About Stemflow's Infiltration Area

This article is a commentary on:

What We Know About Stemflow's Infiltration Area
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$\nDarryl E. Carlyle-Moses$ Darryl E. Carlyle-Moses¹^*

Shin'ichi Iida²

Sonja Germer³

Pilar Llorens⁴

Beate Michalzik⁵

Kazuki Nanko²

Tadashi Tanaka⁶

Alexander Tischer⁵

Delphis F. Levia^7,8

¹Department of Geography and Environmental Studies, Thompson Rivers University, Kamloops, BC, Canada
²Department of Disaster Prevention, Meteorology and Hydrology, Forestry and Forest Products Research Institute (FFPRI), Ibaraki, Japan
³Department of Technology Assessment and Substance Cycles, Leibniz Institute for Agricultural Engineering and Bioeconomy, Potsdam, Germany
⁴Institute of Environmental Assessment and Water Research, Spanish National Research Council (IDAEA-CSIC), Barcelona, Spain
⁵Soil Science, Institute of Geography, Friedrich Schiller University Jena, Jena, Germany
⁶University of Tsukuba, Ibaraki, Japan
⁷Department of Geography & Spatial Sciences, University of Delaware, Newark, DE, United States
⁸Department of Plant & Soil Sciences, University of Delaware, Newark, DE, United States

A Commentary on
What We Know About Stemflow's Infiltration Area

by Van Stan, J. T. II., and Allen, S. T. (2020). Front. For. Glob. Change 3:61. doi: 10.3389/ffgc.2020.00061

Introduction

Stemflow represents the portion of precipitation routed by vegetation to the base of tree boles or plants stems. Van Stan and Allen (2020) (herein referred to as VS&A) is a mini review of studies that have attempted to quantify the infiltration area of stemflow once it has reached the soil surface, I_T. More specifically, VS&A provide an overview of: (i) the ability of vegetation canopies to funnel rainfall; (ii) the various approaches used to estimate or measure the size of I_T; (iii) the different soil properties that may influence the magnitude of I_T, and (iv) the potential for and limitations to using dye and stable isotope tracers in I_T research. The objectives of this commentary are to: (i) highlight and expand upon important points raised by VS&A in order to advance the understanding of the controls regulating the size of I_T, and (ii) provide corrections to and clarification of prior I_T results presented in VS&A.

Advancement of the Scientific Understanding of Stemflow Infiltration Area, I_T

VS&A state the importance of stemflow in the hydrology and biogeochemistry of vegetated environments is dependent upon I_T size. These authors rightfully note that there is a need for further research, especially in natural forest systems, to characterize the size of I_T. Previous studies (e.g., Iida et al., 2005; Chinen, 2007) have estimated the magnitude of I_T using litter marks (the displacement of leaf litter) or soil scour marks caused by the excess overland flow of stemflow. As VS&A state, litter and scour marks are difficult to interpret quantitatively as they neither represent mean nor maximum I_T for a given storm. As such, litter and scour marks have little utility estimating I_T.

VS&A correctly state that factors, such as soil hydrophobicity, could influence stemflow infiltrability in certain environments. Nonetheless, the methodology of Herwitz (1986), in which I_T values are derived by dividing the stemflow volumetric input rate by the infiltration capacity of the surface soil (i.e., the saturated hydraulic conductivity, K_sat), remains a theoretically sound approach. What is important to highlight is that in situ measurements of K_sat, as a surrogate for stemflow infiltrability in the proximal bole/stem area that include the effect of macropore flow (i.e., K_sat measured with no tension; hydraulic head = 0 cm) are likely to be more representative of the actual infiltrability of stemflow than K_sat measured using tension or K_sat values derived from pedotransfer functions [e.g., ROSETTA model—Schaap et al. (2001)], which estimate soil matrix K_sat.

Critique of Reported Formula and Findings of Previous Research

VS&A (page 1) suggest that the following equation (Equation 1 in VS&A) is the funneling ratio derived by Herwitz (1986):

\begin{array}{l} F = \frac{S_{T}}{P \cdot I_{T}} & (1) \end{array}

where F is the funneling ratio (dimensionless), S_T represents stemflow volume (L tree⁻¹), P is precipitation depth (mm), and I_T is the stemflow infiltration area (m² tree⁻¹).

The funneling ratio proposed by Herwitz (1986), however, differs from that of Equation (1) in that the basal area of the tree bole, B (m²), rather than I_T, is multiplied by P in the denominator of the equation:

\begin{array}{l} F = \frac{S_{T}}{P \cdot B} & (2) \end{array}

VS&A (page 2) also suggest that “… Herwitz's (1986) equation for F employs the concept of I_T…”; however, Herwitz (1986) never advocated that B was a surrogate for I_T or that B played any role in I_T size. Instead, and as aforementioned, Herwitz (1986) derived I_T by taking the stemflow input rate and the infiltration capacity of the surface soil into account, and the derived values of I_Twere markedly different than B.

VS&A (page 3) cite various studies supporting their claim that “there are pieces of evidence that suggest that I_T is larger, 10⁻¹ to 10¹ m², than the areas assumed elsewhere, e.g., 10⁻⁴-10⁻¹ m² (Iida et al., 2016; McKee and Carlyle-Moses, 2017; Carlyle-Moses et al., 2018)”. Iida et al. (2016) make no mention of I_T (or stemflow) and it is unclear why this study was cited. Furthermore, the range of I_T provided by Carlyle-Moses et al. (2018) is for conditions of average rainfall / stemflow input rates within mature, natural forests. They are not representative of extreme precipitation events (e.g., Herwitz, 1986) nor orchards or agricultural fields (e.g., Keen et al., 2010) where soil compaction may reduce stemflow infiltrability.

Table 1 of this commentary expands on Table 1 of VS&A to illustrate a fuller range of I_T reported in the literature and provides corrections and / or clarifying statements to some of the results presented in that table. Table 1 of this commentary shows that assessments of I_T under a variety of rainfall, soil, and plant morphological conditions are lacking. The majority of prior studies report the maximum extent of I_T (e.g., Voigt, 1960; Pressland, 1973) or use “litter marks” or erosional soil scouring for estimating I_T (e.g., Iida et al., 2005; Chinen, 2007) which simply do not provide reliable quantitative evidence of average I_T. Litter marks may be seasonal and are at least episodic phenomena persisting across events (e.g., Iida et al., 2005). Litter marks are not created during low intensity events (as stated by VS&A) but rather during peak periods of heavier rain with high stemflow funneling. What does emerge from Table 1 is that studies conducted thus far using in situ dye experiments and direct observations of stemflow infiltration or studies utilizing physically-based approaches such as dividing the stemflow input rate by the soil K_sat suggest that I_T associated with average rainfall and stemflow rates are limited <1 m² tree⁻¹ in environments (e.g., mature, natural forests) where the soil infiltrability can be expected to have a magnitude of order of 1 x 10² or 1 x 10³ mm h⁻¹. Additionally, the findings presented in Table 1 suggest that I_T ≥ 1 m² tree⁻¹ may sometimes arise during large / extreme rainfalls and stemflow rates in these forest environments and under relatively smaller rainfall and stemflow rates in environments (e.g., agricultural plantations, orchards, agroforestry areas, and urban environments) where infiltrability is likely <1 x 10² mm h⁻¹.

TABLE 1

Table 1. Stemflow infiltration areas (I_T) from previous research.

Author Contributions

DC-M was the primary author of the manuscript and a co-originator of the commentary. SI contributed to the text and was a major contributor to the table. SG and PL contributed to the text of the paper, making several editorial changes and suggestions. SG also played a major role in the revision, reconfiguring the table into final form. BM contributed to the text and to the table. KN contributed ideas to the text. AT contributed ideas to the text and contributed to the table. TT contributed to the text. DL contributed to the text, the table and was a co-originator of the commentary. All authors contributed to the article and approved the submitted version.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

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).

References

Aboal, J. R., Morales, D., Hernández, M., and Jiménez, M. S. (1999). The measurement and modelling of the variation of stemflow in a laurel forest in Tenerife, Canary Islands. J. Hydrol. 221, 161–175. doi: 10.1016/S0022-1694(99)00086-4

GENERAL COMMENTARY article

Commentary: What We Know About Stemflow's Infiltration Area

Introduction

Advancement of the Scientific Understanding of Stemflow Infiltration Area, IT

Critique of Reported Formula and Findings of Previous Research

Author Contributions

Conflict of Interest

Acknowledgments

References

Advancement of the Scientific Understanding of Stemflow Infiltration Area, I_T