Review Reports - Spatiotemporal Dynamics of Carbon Sequestration Potential Across South Korea: A CASA Model-Based Assessment of NPP, Heterotrophic Respiration, and NEP

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors conducted an interesting study on the carbon sequestration across South Korea. They use the MODIS-driven CASA-model approach based on NDVI index to show the overall ecosystem potential. The limitations of the presented approach were also discussed and acknowledged.

Even though the manuscript is well organized, it should definitely improve it's presentation of the methods and forlumae. More details are needed to describe the data sources and their applicability. Also, some formulation correction may be needed.

Title: Why it is "Carbon Absorption Capacity" and not "Carbon Sequestration Potential"?

On what temporal scale the model operates on, and how well it represents the spatiotemporal dynamics? The monthly averaging suggests that the author probably talks about an intra-annual dynamics and annual balances.

It seems that the equation on Line 104 is directly related to GPP as it describes the photosynthesis mechanism, and it is not NPP. It is GPP that directly derived from NDVI indexes. What is the difference in the presented CASA-type case?

Line 111 FPAR coefficient is not defined.

Line 135 the RH function looks questionable as in its current form it rather represents an independent sum of temperature and precipitation effects. May it be some mistake here?

Lines 143-145: If the manuscript describes Carbon Sequestration Potential, why to convert and report in the CO2 unites?

Kind regards,

Author Response

Response to reviewer’s comments

Dear Reviewer:

Thank you for reviewers’ valuable advice and comments. We answered faithfully to reviewers’ questions and revised our manuscript by reflecting reviewers’ valuable advice and comments.

Thank you again for reviewers’ kind advice and comments.

Sincerely Yours,

Chang Seok Lee

Reviewer #1

Comments and Suggestions for Authors

Title: Why it is "Carbon Absorption Capacity" and not "Carbon Sequestration Potential"?

☞ We revised the term by accepting reviewer’s valuable comment. Lines 1 – 2, 254 – 255, 329, 417 - 418

☞ We agree that the original version of the manuscript did not clearly state the temporal scale. To address this, we have revised the Methods to explicitly indicate them:

The simulations are conducted at a monthly resolution;
Monthly NEP values are aggregated to derive annual totals;
Spatially, the results are presented at grid level 250m

In addition, we clarified in the Results that the monthly averaging is intended to highlight intra-annual variability (seasonal dynamics), while the annual balance provides a broader perspective on the interannual and regional trends.

☞ In the CASA-type framework applied in this study, the modeling procedure is as follows:

GPP is first estimated based on NDVI, photosynthetically active radiation (PAR), and light-use efficiency parameters.
Net primary production (NPP) is then derived by subtracting autotrophic respiration (Ra) from GPP.
Finally, net ecosystem production (NEP) is obtained as NPP minus heterotrophic respiration (Rh).

Line 111 FPAR coefficient is not defined.

☞ We added the definition in our manuscript. Lines 111 – 112.

Line 135 the RH function looks questionable as in its current form it rather represents an independent sum of temperature and precipitation effects. May it be some mistake here?

☞ In the CASA-type model, Rh is typically represented as a function of both soil temperature and soil moisture, where the two factors act multiplicatively to constrain decomposition rates. We acknowledge that the equation presented in the original paper may have been misleading, as it appeared to express Rh as an additive combination of temperature and precipitation effects. This was a presentation issue rather than a modeling mistake. To avoid confusion, we have revised the Methods to correctly present the multiplicative form and clarified the role of temperature and water availability.

Lines 143-145: If the manuscript describes Carbon Sequestration Potential, why to convert and report in the CO2 unites?

☞ Carbon sequestration potential can be expressed either in terms of elemental carbon (C) or in CO₂-equivalent units. In our manuscript, we chose to present the results in CO₂-equivalent units (t CO₂ ha⁻¹ yr⁻¹) to facilitate comparison with climate policy targets, carbon offset markets, and international reporting systems, which are most commonly expressed in CO₂ units.

We agree, however, that from a biogeochemical perspective, expressing results in elemental carbon (g C m⁻² yr⁻¹) is more precise and directly consistent with ecosystem process modeling. To address this, we have revised the manuscript to:

Present the primary results in C units (g C m⁻² yr⁻¹);
Provide CO₂-equivalent values in parentheses where appropriate, to maintain relevance for policy interpretation and broader applicability.

Kind regards,

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Currently, one of the policy directions in the field of ecology and nature management in highly industrialized developed countries is to reduce greenhouse gas emissions, assess carbon pools and fluxes by terrestrial ecosystems, identify sources of gas intake, set limits on the formation of carbonaceous compounds, etc. The creation of carbon farms, the study of carbon balance in terrestrial ecosystems, the establishment of features of carbon deposition by forest biogeocenoses in the context of the new climate agenda is not a complete list of research areas. Also, one of the relevant areas of study is to establish the spatial and temporal dynamics of carbon uptake/emission by natural objects. At the same time, this problem can be considered both at the local and global (biospheric) levels of ecosystem organization. Despite the fact that there are a lot of works in this area, there are blank spots. This is due to a lack of funding and human resources to organize full-scale, large-scale research, as well as, to put it mildly, the unwillingness of individual governments to show their negative, anthropogenic impact on nature. The latter is known to be one of the sources of changes in the carbon balance in the biosphere. The lack of information on relevant topics has determined the importance of the article offered to our attention.

The article is written in good language, all scientific terms are used correctly. In this regard, the article will be understandable and in demand by specialists from different countries, they will be able to compare the results with the results obtained. It is also very important that the authors test their data, so that the country's contribution to the total flow of greenhouse gases into the biosphere can be assessed and modern issues can be addressed. The tabular material is very interesting, the drawings are informative. The conclusions correspond to the stated goal. A large literature review allows the authors to correctly interpret the data obtained. It should be noted that calculations of spatial and temporal changes in indicators can be recommended for use in monitoring studies of the natural environment. In general, the work makes a good impression, the comments are presented below.

2- Change the name

Calculation and Spatiotemporal Dynamics of Carbon Absorption Capacity...where? In what?

-terrestrial ecosystems

-rivers, seas, lakes

-Natural landscapes

- forest ecosystems?

South Korea?...if you write "wide, very wide!" like that, then you can close your way further ... a dead end. Can I clarify? Do it more locally?

19- In 2024, national NPP totaled 78.63 Mt CO₂ yr⁻¹ (mean: 19 56.63 t CO₂ ha⁻¹ yr⁻¹).Point.

Next, combine the two sentences into one.

99-Materials and Methods

2.1. Methods…

Maybe we need materials first?

167-IDW...what is it?decrypt

169 is a very unclear drawing, change

193/204 is not a clear drawing, please provide the coordinates. It is not clear what is the piece in the lower right corner?

137- what is (k, a, b, rh)

224- change the numbers 1,000 to 1.00

225- The temporal trends of the total (upper) and mean (lower) NPP (MtCO2/yr) for 15 years 225 from 2010 to 2024...where?/in what? in South Korea

Please check all the captions to the drawings... specify the name

224- why this offer?

260-Spatial analysis? Is that so? To clarify...there is no need for methods

288- Relationship (what? Who?) with Climatic and Vegetation Factors...

464- I'm not sure if South Korea is a carbon sink. A highly developed country, high anthropogenic pressure on nature..I recommend writing... "According to the conducted research"... "based on our calculations"…

In conclusion, I would like to thank you once again for the good materials and wish you creative success.

Comments on the Quality of English Language

The scientific terms are clear, there are no style issues.

Author Response

Response to reviewer’s comments

Dear Reviewer:

Thank you for reviewers’ valuable advice and comments. We answered faithfully to reviewers’ questions and revised our manuscript by reflecting reviewers’ valuable advice and comments.

Thank you again for reviewers’ kind advice and comments.

Sincerely Yours,

Chang Seok Lee

Reviewer #2

Comments and Suggestions for Authors

☞ We sincerely thank the reviewer for this thoughtful and encouraging comment.

2- Change the name

Calculation and Spatiotemporal Dynamics of Carbon Absorption Capacity...where? In what?

-terrestrial ecosystems

-rivers, seas, lakes

-Natural landscapes

- forest ecosystems?

South Korea?...if you write "wide, very wide!" like that, then you can close your way further ... a dead end. Can I clarify? Do it more locally?

☞ We thank the reviewer for this valuable comment and acknowledge that the original wording of the title and manuscript did not clearly indicate the study's spatial and ecosystemic scope. We revised our manuscript by accepting reviewer’s valuable comment. Lines 105 – 108.

19- In 2024, national NPP totaled 78.63 Mt CO₂ yr⁻¹ (mean: 19 56.63 t CO₂ ha⁻¹ yr⁻¹). Point.

Next, combine the two sentences into one.

☞ We revised the part by accepting the reviewer’s valuable comment as the follows. In 2024, national NPP totaled 78.63 Mt CO₂ yr⁻¹, with a mean value of 1956.63 t CO₂ ha⁻¹ yr⁻¹.

99-Materials and Methods

2.1. Methods…

Maybe we need materials first?

☞ We revised our manuscript by accepting the reviewer’s valuable comment. Lines 105 – 126.

167-IDW...what is it?decrypt

☞ We revised this part to reduce misunderstanding of the readers. Line 116.

169 is a very unclear drawing, change

☞ We improved Figure 1 by accepting the reviewer’s valuable comment.

193/204 is not a clear drawing, please provide the coordinates. It is not clear what is the piece in the lower right corner?

☞ We improved the figure by accepting the reviewer’s valuable comment.

137- what is (k, a, b, rh)

☞ We added a description of the symbols. Lines 162 – 165.

224- change the numbers 1,000 to 1.00

☞ We revised this part by accepting the reviewer’s valuable comment. Figure 2(line 236), Figure3(line 249), Figure4(line 260)

225- The temporal trends of the total (upper) and mean (lower) NPP (MtCO2/yr) for 15 years 225 from 2010 to 2024...where?/in what? in South Korea

Please check all the captions to the drawings... specify the name

☞ We thank the reviewer for this important suggestion. We agree that several figure captions in the original version did not explicitly state the spatial scope, which may cause ambiguity.

To address this:

We revised the caption for Figure 2,3,4 as follows:

- Original: “The temporal trends of the total (upper) and mean (lower) NPP (MtCO₂/yr) for 15 years from 2010 to 2024.”

- Revised: “The temporal trends of the total (upper) and mean (lower) NPP (MtCO₂/yr) across terrestrial ecosystems of South Korea for the 15-year period from 2010 to 2024.”

We systematically reviewed all figure captions and specified the study area (South Korea) and ecosystem scope (terrestrial ecosystems, forest, cropland, etc.) wherever relevant.
We also ensured that each caption now provides sufficient detail, including units and time period, so that the figure can be understood independently from the main text.
The area is represented by Figure 1.

224- why this offer?

☞ What does this question mean?

260-Spatial analysis? Is that so? To clarify...there is no need for methods

In the original version, our use of the term “spatial analysis” may have been ambiguous. To clarify: our study does not introduce a new spatial analysis technique, but rather applies existing geospatial interpolation and mapping approaches (e.g., Inverse Distance Weighting, CASA model outputs) to analyze the spatiotemporal dynamics of NPP/NEP across South Korea. Lines 268-270.

In line with the reviewer’s suggestion, we have:

Revised the text to avoid overstating this as a “spatial analysis.”
The spatial distribution analysis (Figure 3) revealed that mountainous regions exhibited higher NEP values compared with lowland and urban areas.
According to the reviewer’s suggestion, Figure 3 has been revised for improved clarity. The caption (line 250) has also been updated to better reflect the content and spatial interpretation of heterotrophic respiration.

288- Relationship (what? Who?) with Climatic and Vegetation Factors...

☞ We revised this part to reduce misunderstanding of the readers. Line 338

☞ You are right. South Korea emits much CO₂. However, as was expressed in our manuscript, South Korea’s terrestrial ecosystems act as a significant carbon sink.

In conclusion, I would like to thank you once again for the good materials and wish you creative success.

☞ Thank you for your kind encouragement.

Comments on the Quality of English Language

The scientific terms are clear, there are no style issues.

☞ Thank you very much.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Please find the comments attached to the review PDF file.

Comments for author File: Comments.pdf

Author Response

Response to reviewer’s comments

Dear Reviewer:

Thank you for reviewers’ valuable advice and comments. We answered faithfully to reviewers’ questions and revised our manuscript by reflecting reviewers’ valuable advice and comments.

Thank you again for reviewers’ kind advice and comments.

Sincerely Yours,

Chang Seok Lee

Reviewer #3

Review Report #

Article: Calculation and Spatiotemporal Dynamics of Carbon Absorption Capacity across South Korea

Authors: Nam-Shin Kim, Jae-Ho Lee and Chang-Seok Lee

General Comments

The article aimed to: (1) quantify the temporal and spatial variability of NPP and NEP across vegetation types and climate drivers in South Korea; (2) identify long-term carbon sink trends from 2010 to 2024; and (3) explore regional implications of NEP distribution in the context of carbon neutrality and NbS.

Congratulations to the authors. The article is interesting, very well written, with a robust introduction based on current bibliographies. The methodology is clearly described, uses robust statistical analyses and allows for reproduction in other studies with similar characteristics. The results are clearly described and were well explored and discussed. The conclusions reflect the results and are consistent.

Throughout the pdf file, I have highlighted most of the cases that require revision regarding the insertion of acronyms, as well as the places where I am recommending the replacement of terms written in full, by their respective acronyms and vice-versa. The article can be published in Sustainability, after the suggested corrections have been addressed.

☞ Thank you very much for kind valuable advice and comments. We revised our manuscript by accepting the reviewer’s valuable comments. Line 20, Lines 80 – 81, 130, 132, 136, 137, 144 - 145, 147,155, 156,170, 172,181,183,123,126, 273, 301, 304, 395, 479 – 483, 752 - 757

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I would like to thank authors for conducting the proper revisions and addressing all the highlighted concerns. I think that manuscript is now in good shape to be published in its current form.