Tree Roots Anchoring and Binding Soil: Reducing Landslide Risk in Indonesian Agroforestry
Round 1
Reviewer 1 Report
The paper evaluated the role of tree roots in strengthening soil. The paper is generally well written and the methods are well described. I have few comments on the paper. They are mainly clarification.
I suggest the authors to unify their units expression in SI.
Table 1. Soil type seems to be a mixture of USDA, Indonesian and WRB classification. Please unify them.
L.137. A diagram of the instrument would be interesting. Note it is a tensile strength, and you used "shear" which could confuse the sentence. Should be: "The mean of six replicates of the force required to break the root was used as a measure of root tensile strength"
L.141 unfinished sentence lignin and polyphenols measured using ???
L.144 I am not sure if root only contributes to soil's shear strength, it should also contribute to tensile and compressive strength
How was soil shear strength measured?
L.159 double ring?
Maybe the authors could think that by doing this study, they had contributed to the damage of roots. The trees have to suffer.
L.175 dbh or DBH?
L.177 ????
L.179 I did not see the k-means clustering result? Table 2?
L.185 Root tensile strength would be a function of moisture content. I would expect the effect of moisture is different to soil, i.e. higher moisture would increase tensile strength as the roots will be more pliable
L.190 decline as tree aged?
Fig 3 y-axis Strength , should be in kPa
L. 208 root length density, better expressed in SI units? (m/m^3)
L.219 units, better all uniform in SI kg/m3
L. 200 SI units? m/kg
L.231 strength of 3.37 MPa is very high. Please check!
L. 246-249, Where do these 2 equations derive from?
Fig 6 & 7, In addition to root density and length, it is also the root strength. So would be good to have a regression relating soil strength with root density and root strength
Table 2. IRA and IRB, I haven't seen any correlation between IRA with soil strength?
Table 2. No.6, Surian or Durian? I prefer durian.
Author Response
Reviewer 1
The paper evaluated the role of tree roots in strengthening soil. The paper is generally well written and the methods are well described. I have few comments on the paper. They are mainly clarification.
[** Thank you for the positive and constructve comments!]
I suggest the authors to unify their units expression in SI.
[** yes, we have done so, thanks]
Table 1. Soil type seems to be a mixture of USDA, Indonesian and WRB classification. Please unify them.
[** We did i.e. Cambisol=Inceptisol; Latosol=Inceptisol. thanks]
L.137. A diagram of the instrument would be interesting. Note it is a tensile strength, and you used "shear" which could confuse the sentence. Should be: "The mean of six replicates of the force required to break the root was used as a measure of root tensile strength"
[** We added a figure 2 of methods for measuring soil shear resistance]
L.141 unfinished sentence lignin and polyphenols measured using ???
[** thank you for spotting our mistake. We completed the sentence.]
L.144 I am not sure if root only contributes to soil's shear strength, it should also contribute to tensile and compressive strength
[** we revised and clarified the terminology]
How was soil shear strength measured?
[** Same comment as in L 137: we added a figure and some text]
L.159 double ring?
[** we hope the figure helps clarifying this]
Maybe the authors could think that by doing this study, they had contributed to the damage of roots. The trees have to suffer.
[We added a comment in the discussion on our ‘non-destructive‘ method]
L.175 dbh or DBH?
[we now only use dbh]
L.177 ????
[** removed]
L.179 I did not see the k-means clustering result? Table 2?
[** we removed this from the methods and don’t show the results]
L.185 Root tensile strength would be a function of moisture content. I would expect the effect of moisture is different to soil, i.e. higher moisture would increase tensile strength as the roots will be more pliable
[** Yes, measurements in the dry season might be different; all our measurements were during the rainy season]
L.190 decline as tree aged?
[**for the coffee the 7 year old, trees indeed had lower Lrv values – we commented on that in the text]
Fig 3 y-axis Strength , should be in kPa
[**Thanks, we corrected]
- 208 root length density, better expressed in SI units? (m/m^3)
[** we shifted to km m-3] for Lrv]
L.219 units, better all uniform in SI kg/m3
[** and kg m-3 for Drv]
- 200 SI units? m/kg
[and for Specrol m/g]
L.231 strength of 3.37 MPa is very high. Please check!
[** confirmed]
- 246-249, Where do these 2 equations derive from?
[** we removed this section]
Fig 6 & 7, In addition to root density and length, it is also the root strength. So would be good to have a regression relating soil strength with root density and root strength
[** we couldn’t follow this suggestion as root strength was not measured at the same units, wecan only connect at aggregated species level]
Table 2. IRA and IRB, I haven't seen any correlation between IRA with soil strength?
[** Indeed, we did not measure soil strength for the same units as the IRA/IRB assessments; the conceptual link is via root length density, allometrically related to the proximal root diameters]
Table 2. No.6, Surian or Durian? I prefer durian.
[** we opted for the spelling ‘suren’ for Toona to avoid confusion]
Reviewer 2 Report
Comments from Reviewer
The authors present a very interesting and practically applicable study that tested and validated the hypothesis that tree root system stabilize hillslopes and riverbanks thereby reducing risk of landslides. 5 test sites and many tree species were explored in the context of productive coffee agroforestry systems. The influence of lignin, Nitrogen, and Carbon content, shear strength, root length density, root tensile strength and several other indices including Index of root anchoring and Index of soil binding were used to validate the claim. Chemical tests were conducted to quantify the chemical content of roots. Finally, ANOVA was carried out on extensively collected data to get meaningful correlations.
In general, this article is well written in English. However, the written English grammar could be improved. The authors are using sufficient number of tests for this study. Technical interpretation of all test results is sound.
I do have a few concerns and suggestions which I have listed below, hopefully to improve the manuscript.
Comment 1: Page 1, lines 11-12: Original sentence is “Tree root systems stabilize hillslopes and riverbanks, reducing landslide risk, but data for the humid tropics are scarce.”
Suggested sentence is: “Tree root systems stabilize hillslopes and riverbanks, reducing landslide risk, but related data for the humid tropics are scarce.”
Comment 2: Mandatory Correction: Page 7, Section 3.3: Soil Shear strength: The authors discuss about shear strength test results but fail to explain how they performed soil shear strength tests. They do mention about reference [47]. This reference is a big textbook and reader can get easily lost. Thus, it is important to briefly describe test method for quantifying shear strength. Was it direct shear strength test? What was size of shear box? I am also interested in knowing how they determined soil-root shear strength? Please explain in brief.
Comment 3: Mandatory Correction: Page 7, Section 3.2: Tree root length density: The authors discuss about Lrv for different tree species and refer that they used reference [48] to find it. However, for the sake of readers, they need to explain method of how they found Lrv in brief. Please discuss experimental method in finding Lrv in short.
Author Response
Reviewer 2
The authors present a very interesting and practically applicable study that tested and validated the hypothesis that tree root system stabilize hillslopes and riverbanks thereby reducing risk of landslides. 5 test sites and many tree species were explored in the context of productive coffee agroforestry systems. The influence of lignin, Nitrogen, and Carbon content, shear strength, root length density, root tensile strength and several other indices including Index of root anchoring and Index of soil binding were used to validate the claim. Chemical tests were conducted to quantify the chemical content of roots. Finally, ANOVA was carried out on extensively collected data to get meaningful correlations.
[** Thank you foor the positive and constructive comments!]
In general, this article is well written in English. However, the written English grammar could be improved.
[** Thank you, we have further checked the revised text]
The authors are using sufficient number of tests for this study. Technical interpretation of all test results is sound.
I do have a few concerns and suggestions which I have listed below, hopefully to improve the manuscript.
Comment 1: Page 1, lines 11-12: Original sentence is “Tree root systems stabilize hillslopes and riverbanks, reducing landslide risk, but data for the humid tropics are scarce.”
Suggested sentence is: “Tree root systems stabilize hillslopes and riverbanks, reducing landslide risk, but related data for the humid tropics are scarce.”
[** OK, adjusted]
Comment 2: Mandatory Correction: Page 7, Section 3.3: Soil Shear strength: The authors discuss about shear strength test results but fail to explain how they performed soil shear strength tests. They do mention about reference [47]. This reference is a big textbook and reader can get easily lost. Thus, it is important to briefly describe test method for quantifying shear strength. Was it direct shear strength test? What was size of shear box? I am also interested in knowing how they determined soil-root shear strength? Please explain in brief.
[** as also requested by reviewer 1, we added a figure and text to explain the measurements]
Comment 3: Mandatory Correction: Page 7, Section 3.2: Tree root length density: The authors discuss about Lrv for different tree species and refer that they used reference [48] to find it. However, for the sake of readers, they need to explain method of how they found Lrv in brief. Please discuss experimental method in finding Lrv in short.
[** we have added the requested detail in the methods section 2.3]
Round 2
Reviewer 2 Report
I am satisfied by the authors response. The manuscript is now improved and could be accepted for possible publication.
