Immediate Effects of Prescribed Fire on Sub-Surface Water Quality in a Managed Yellow Pine Forest

Round 1

Reviewer 1 Report

Overview:

This study evaluates short-term effects of prescribed burning on soil inorganic N and P. While this topic has been well-studied and post-fire soil nutrient patterns well-documented across the United States, this study contributes additional information for managed timber crop stands in the SE U.S. Additional description of the fire history and management of the ecosystem and examples from other systems would help to provide context to both the Introduction and Discussion. Additionally, some justification of running both ANOVAs and RM ANOVAs is needed, along with more detail around that statistical analyses used. Please see line-by-line comments below for more information.

Line-by-line comments:

Abstract:

• Clarify that you’re working in managed timber crop stands
• Add a brief description of the fire here - intensity, severity, season, etc.

Introduction:

• Additional information on the fire history and management of this ecosystem is needed to provide some context.
• A lot is already known about effects of prescribed fire and wildfire on soil nutrients from decades of research – it would be good to include some of those findings here and to clarify if/how this study adds to the existing knowledge base.

Methods:

• Figure 2 map is missing
• Ln105: How were the lysimeters that didn’t have sufficient water in them distributed across the treatments/watersheds?
• Make sure to maintain consistent 1^st or 3^rd person writing throughout.
• Ln125-127: Run-on sentence
• Did your data meet all requirements for ANOVA?
• It’s not clear why you ran both ANOVA (two-way?) and repeated measures ANOVA – seems you could have just run RM ANOVA. Not sure if comparing overall 5-month means are very useful since you expect there to be substantial temporal variation (i.e., initial spike) in concentrations. Also, please clarify what your independent and dependent variables were (and did you evaluate interactions?). What post-hoc test(s) did you run?

Results:

• Ln133: remove the word ‘was’ so the sentence reads ‘…with minimal bare soil exposed’.
• Ln156: Would be good to introduce this issue of toxicity thresholds with some cited examples in your Introduction so the first mention of it isn’t in your Results. It seems to come out of the blue here.
• Ln158: please add the p-value outcome from the RM ANOVA here.
• Ln167: mean PO4 averaged across all sampling time points?
• Ln183: change statistical to statistically
• Ln184: do you mean seasonal trends here?

Discussion:

• Often best to start your discussion with an overview of the relevance and context within which your findings sit. I’d recommend including a paragraph before your subsections that provides a brief, well-cited overview of why these findings are important.
• Ln197-200: this basically repeats what is stated in Ln191-193 but with more detail and explanation. I’d recommend combining these sentences.
• Ln214-217: Some additional explanation here with examples would be helpful to provide context

Conclusions:

• Ln232-233: Not true to say that few studies have examined the effects of Rx fire on inorganic P – this has been evaluated across the country for over 30 years in forests, shrublands, wetlands, grasslands, etc. Maybe better to focus in your statement a bit here to clarify that few studies within your study ecosystem have evaluated effects on soil P. Also, one of the papers cited here (Binkley et al. 2004) did not evaluate Rx fire effects on soil P. There are over 50 other papers you could cite here.

All Figures: Consider readjusting your x-axis to show more of the dates (especially showing the first and last dates. Also, please add asterisks above the timepoints that had significant differences between treatments.

Figure 1: missing the vertical line showing when the burn took place.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This is a really nice, well written paper that looks into the effects of a low severity prescribed burn on sub-surface nutrient pools in a mixed conifer forest at the Jocassee Gorges Management area, South Carolina, over the course of 5 months. The objectives of the paper are clear, and I think the findings will be of interest to a wide variety of audiences.

There are just some minor comments, that I feel will improve the clarity of a couple of points made, as well as the addition of a key figure that is currently missing from the manuscript.

Line 37: “low severity” – please define what is meant by low severity for readers who may be unfamiliar

Figure 2 is missing

Treatments: Line 90 to 95: I think this needs to be clearer. Does this mean you had 10 transects of 2 lysimeters at the ‘upslope’ position and 10 transects of 2 lysimeters 30 m away at the ‘downslope’ position? Maybe this becomes clearer with the map?

Line 94-95: “two transects in each burned stand were randomly designated as burn controls" – again may be this becomes clearer with the map?

Table 1: I think it would be good to have some of the raw data that was collected, maybe as a separate table in the appendix

Line 43: please add ‘of’: “ in the absence of plant re-uptake”

Line 58 – comma needed – after ‘health’

Line 74 – ‘and’ to be inserted before ‘white oak’.

Line 74 – 75 ‘Loblolly pine (Pinus taeda L.) plantations are also found in some lower elevation sites’

Line 77: reference required following ‘which is characteristic of yellow pine forests’

Line 133: ‘with minimal bare soil was exposed’ change to ‘where bare soil was exposed’

Line 171: You say that the levels did not experience a notable return to baseline – from Figure 5. Although it appears that concentrations reached ‘baseline’ levels around the last sample taken? Could you edit to say that levels did not return towards baseline until the final sample reading? Or explain why you think levels did not return to baseline.

Line 181: “predicted peak was unaffected by burn treatment” – this currently implies that there were different burn treatments tested, so maybe needs clarification. You could add in “predicted peak was unaffected by the low severity burn treatment”

Line 183: “statistical” to “statistically”

Discussion:

Line 191 – define what temperature NO₃^- is volatized

Lines 197 to 199: “Additionally, N response to fire is strongly associated with soil heating; low severity fuel-consumption, low soil heating and low total N in both litter and soil are the primary factors explaining the lack of NO₃^- response in this study” I feel this needs more explanation as to why you don’t see a difference between the control and after burn NO₃^- values. This is particularly important also when the reader gets to the conclusion, as there is a suggestion of a reduction in N nutrient pools, yet from your data it appears that N remained the same after the burn as before, not lower?

Line 232 - 233: comma needed: “... and those that have, ……”

Line 243-244: Can you really say that P loss is ecologically insignificant? P, like N is a limiting nutrient for primary producers, so must have some significance?

Line 247 – 249: Sentence needs re-wording. E.g. “This study shows that the nutrient responses observed…..”

Line 249: “The prescribed fires appear to have had no discernable effect...”

Line 250: “soil solution NO₃. We hypothesize that this is due to NO₃^- being highly mobile and requiring low volatilization energy”

As this is an inference made.

Line 251: see previous comment for Lines 197 to 199.

Line 253 – 255: “…but it is unlikely that the observed PO4^3- response to prescribed fire will impact watershed resources due to functionally inhibited leaching in acidic soils” - could this be an area that requires further study in the future? e.g. you could add “although further study would be required to corroborate this”.

Line 256: “tendency of PO₂^3- to bind to....”

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Reviewer

General Comments:

The study demonstrates how prescribed fires affects the soil properties from the concentration of micronutrients (ammonium, nitrate and orthophosphate) and pH during 5-months. This presents an interesting approach, and has great potential to increase the knowledge base and fire management strategies. The conclusions are supported by the data and the organization of the manuscript is appropriated. However, a few changes are necessary to improve understanding of this manuscript:

Specifics Comments

Lines 15-16: The prescribed burning carried out in the area needs to be better characterized. It is necessary to better define in the abstract and in the materials and methods what is a low-severity prescribed fire, the period of the day that it was carried out, and the meteorological conditions of the day of the fire. It is also necessary to better characterize the vegetation that was burned. For example, its flammability.

Lines 20-21: In this sentence “Soil solution pH and NO3- parameters were unaffected by prescribed fire application” the authors need to make it clearer. These results correspond to which measurement parameter (mean, maximum or predicted Gaussian peak values) and to which time scale (beginning, middle or end)? In addition, the differences found for the pH (mean) in the first months are evident in the figure 6, and need to be highlighted in the abstract and results.

Lines 32-33: Include here what are the benefits of the prescribed burning in this region. Have these strategies been effective? Isn't there any work that assessed the impacts of fire on this region?

Lines 45-46: The possible impacts of increasing pH concentration on the environment must also be included.  In addition, the relationships between pH changes and their impacts on the ecosystem need to be further developed in the introduction and discussion

Lines 96-97: Where's figure 2?

Lines 118-129: Include the references of the statistical analyses and justify the use of estimate Gaussian peak values in this study.

Lines 136-137: The actors need to justify which of these parameters (mean, maximum or predicted Gaussian peak value) has the greatest weight to justify the differences between treatments.

Comments for author File: Comments.docx

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

This is a brief review. While this is an interesting study, the presentation of the idea and work in this manuscript needs revision before a more thorough review of the manuscript can be completed. As is, I don’t feel entirely comfortable making a final assessment of the quality and correctness of this research. Currently, I could not repeat this study as the methods are incomplete.

Other:
Water quality is important part of the paper, but the title does not reveal this. The abstract has only one line about a result about water quality.

There are number of places where more complete explanations of concepts, descriptions, procedures, etc can be provided to aid the reader in following the narrative (see marked up manuscript).

-Does the introduction provide sufficient background and include all relevant references?

In general, there is a dearth of citations in this manuscript.

-Is the research design appropriate?

I am unable to fully evaluate the technical soundness as the Methods are, in my opinion, incomplete.

-Are the methods adequately described?

No. Statistic procedure section is incomplete; insufficient detail regarding analyses. The descriptions of ‘stands’ is confusing. Sample size is not clearly presented.

-Are the results clearly presented?

No. Please consider revising to make the document easier for the reader. Please do not report “naked” p-values. Sample size is not clearly presented.

-Are the conclusions supported by the results?

Unsure, other manuscript sections (and this one) are incomplete or unclear.

- Have they been fair in their treatment of previous literature?

Fair, where citations are provided. However, I think there are several places where there needs to be more citations.

Please see attached document for more comments and questions.

These papers may be helpful:

Brockway, D.G. and C.L. Lewis. 1997. Long-term effects of dormant-season prescribed fire on plant community diversity, structure and productivity in a longleaf pine wiregrass ecosystem. Forest Ecol. Managem. 96:167– 183.

Ficken, C.D., Wright, J.P., 2017. Contributions of microbial activity and ash deposition to post-fire nitrogen availability in a pine savanna. Biogeosciences 14, 241–255. https://doi.org/10.5194/bg-14-241-2017

Schafer, J.L., et al, 2013. Current and historical variation in wiregrass (Aristida stricta) abundance and distribution is not detectable from soil δ13C measurements in longleaf pine (Pinus palustris) savannas. Castanea 78, 28–36. https://doi.org/10.2179/12-021

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Klimas et al have addressed most of my previous concerns for their manuscript now titles “Immediate Effects of Prescribed Fire on Sub-Surface Water Quality in a Managed Yellow Pine Forest.” Thank you. I have included some comments below, some are reiterations of my previous concerns that have yet to be full addressed. One general comment is that in some places information is still lacking, that if included would help the reader follow the narrative. I’d prefer that the onus of understanding the paper be put on the author, not the reader. That said, perhaps ask someone in a comparable field who didn’t work on the paper to see if anything is ‘missing’.

Line 9: “acres”

Line 31: “2 million forested acres”.

Please use SI units.

https://www.mdpi.com/journal/fire/instructions#preparation

Line 34-37: “Yet contemporary knowledge on the immediate effects of prescribed fire on nutrient cycling and sub-surface water quality in managed timber crop forests remains limited in the Southern Appalachian Mountains, where it is practiced extensively to meet productivity and forest health objectives”

What about traditional knowledge?

Line 70-71: “Regulating agencies have established concentration standards in surface waters to protect the value of forested watersheds as sources of clean water2,20.”

Standards are not to protect clean water?

Line 85: “2.1. Site Description”

Include geographical coordinates?

Line 92: proofread

Line 97-98: “Temperature and precipitation data were collected weekly at the field site (Figure 1).”

Thanks for adding this content after my comment in my previous review, but there is still missing information. How did you collect this information? Which tools did you use? Without this information I cannot repeat your experiment.

Line 105: “dormant understory woody vegetation”

By March 5^th in SC, would all the understory woody plants still be dormant? In natural systems, likely no. I am not sure about a managed timber system. Thanks.

Line 114: How were the control transects excluded from burning?

Line 145: How did you conduct the t-tests?

Line 154: What are “further differences”? I think that post-hoc tests have a more specific function.

Lines 157-159: “The litter layer was partially consumed but the underlying duff layer experienced minimal charring. Litter was retained in gully bottoms and burning was minimal in other mesic areas.”

This is the first and only time the authors write about “gully bottoms” and “other mesic areas”. Surely, if this is important to the reader, the authors will provide more context.

Line 165: How is the temperature aggregated / summarized by week? I’ll assume rainfall is a weekly sum, but you might want to state that.

Lines 192-193: “Prescribed fire increased the maximum available inorganic PO43- concentrations at 30cm depth relative to the control (Table 2).”

It did? Or, was there a relationship/correlation between the two?

Lines 249-251: “Fire seasonality, in this study, played a key role in limiting the pulse of NH4+, as prescribed fires conducted at the end of or during the growing season may result in an extended period of elevated nutrient pools in the absence of plant regeneration or microbial activity5,7,14,35”

Did I miss the application of more prescribed fires throughout the season? I thought this study had just one fire event. If there was just one fire how can the authors state “Fire seasonality, in this study, played a key role in limiting the pulse of NH4+”? This seems definitive rather than suggestive or plausible, I would think this would need to be evaluated against later year fires too. Right?

In the authors response to my previous comment:

“Ln130: The authors do not present any test statistics.” The authors responded: “Test statistics have been added where relevant when reporting the results of the repeated measures ANOVA. “Naked” p values have been removed to reduce redundancy between the body text and tables.”

However, it appears to me that there is still a dearth of test statistics (are they any that are reported?) and naked p-values are still present (e.g., Lines 183, 185, 195, 204). Please advise.

Finally, what is the utility of the lines “connecting the dots” in Figures 2-6? I do not understand what information that are providing.

Author Response

Please see the attachment

Author Response File: Author Response.docx