Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This article has high scientific value and practical significance in studying the spatial distribution and temporal changes of carbon storage in forest and grassland ecosystems in China's nature reserves (NRs), but there are some areas need further improvement. Thus, a recommendation of "Minor revisions" is suggested to this article. 

1: There is a grammatical error in the fourth line of the abstract. We used NDVI values ​​to assess... or Based on NDVI values, we assessed...

2: There is a grammatical error in the ten line of the Introduction. "enhanced" not enhance.

3: In “2. Method”, “The data sets from Luo et al. (2013) and Song et al (2018) were used to obtain” should clearly indicate what data the dataset contains and what its resolution and quality are?

4: Ensure consistency in terminology, e.g., "Carbon storage" in the last sentence of the second paragraph of the introduction and in line 21 of section 4.1 should be C storage. You should check the entire paper carefully.

5: It is recommended to revise the title of 3.1 to “Temporal trends in C Storage” to correspond to the title of 3.2 “Spatial distribution of C growth rates in various NR”.

6: The title of 4.1 can be changed to "4.1 Heterogeneity in Vegetation-Specific Carbon Storage Trends", which is more in line with the writing standards of the paper and the summary of the discussion content.

7: The title of 4.2 can be changed to "4.2 Spatial patterns of C Storage growth in Nature Reserves" to match your discussion.

8: In section 4.3 you discussed that nature reserves play a key role in carbon storage and you provided evidence to support this point. Therefore, the title of section 4.3 should be changed to “Effectiveness of Nature Reserves in forest C conservation”.

9: References should be uniform, some have DOI numbers and some do not.

 

 

 

 

 

Author Response

The reviewer 1:

 

This article has high scientific value and practical significance in studying the spatial distribution and temporal changes of carbon storage in forest and grassland ecosystems in China's nature reserves (NRs), but there are some areas need further improvement. Thus, a recommendation of "Minor revisions" is suggested to this article.

 

1: There is a grammatical error in the fourth line of the abstract. We used NDVI values ​​to assess... or Based on NDVI values, we assessed...

R: Accepted

2: There is a grammatical error in the ten line of the Introduction. "enhanced" not enhance.

R: Accepted

3: In “2. Method”, “The data sets from Luo et al. (2013) and Song et al (2018) were used to obtain” should clearly indicate what data the dataset contains and what its resolution and quality are?

R: Accepted. The individual plot biomass data sets (1607 plots) from Luo et al. (2013) and Song et al (2018) were used to obtain.

4: Ensure consistency in terminology, e.g., "Carbon storage" in the last sentence of the second paragraph of the introduction and in line 21 of section 4.1 should be C storage. You should check the entire paper carefully.

R: Checked.

5: It is recommended to revise the title of 3.1 to “Temporal trends in C Storage” to correspond to the title of 3.2 “Spatial distribution of C growth rates in various NR”.

R: Accepted

6: The title of 4.1 can be changed to "4.1 Heterogeneity in Vegetation-Specific Carbon Storage Trends", which is more in line with the writing standards of the paper and the summary of the discussion content.

R: Accepted

7: The title of 4.2 can be changed to "4.2 Spatial patterns of C Storage growth in Nature Reserves" to match your discussion.

R: Accepted

8: In section 4.3 you discussed that nature reserves play a key role in carbon storage and you provided evidence to support this point. Therefore, the title of section 4.3 should be changed to “Effectiveness of Nature Reserves in forest C conservation”.

R: Accepted, thanks!

9: References should be uniform, some have DOI numbers and some do not.

R: Checked.

 

Reviewer 2 Report

Comments and Suggestions for Authors

This study assessed vegetation carbon (C) storage trends in China’s nature reserves (NRs) from 2000 to 2015 using NDVI data, revealing a 63.06% overall increase of 60.05% in forests and 86.33% in grasslands. Forest C density was higher inside NRs than outside, highlighting the important role of NRs in forest carbon conservation, despite limited impact on grassland carbon protection. I would recommend a minor revision for this paper.

 

Some spelling and grammar issues that authors need to check throughout the MS.

Some examples:

"polution" to "pollution"

"enhance ecosystem resilience" should be "enhances" to match "also provides"

"multi-variate" to "multivariate"

“in this 15 years” to “over these 15 years”

“so we obtained different regression models for different vegetation types”, reword to avoid repetition, e.g., “yielding distinct regression models per vegetation type

 

Include an explicit study hypothesis or objective statement at the end of the Introduction

 

Some major comments:

Section 3.2:

Quantification of "growth rate":

It's unclear whether "growth rate" refers to absolute changes in C stock, percent changes, or regression slope over time. Please clarify the metric and units.

 

Uneven treatment of forest vs. grassland:

 

Forest C dynamics are described in more detail than grasslands. Consider balancing the narrative or explaining why grasslands receive less attention.

 

Clarify how spatial differences were calculated. Did you use grid-level NDVI changes within each NR, or aggregate statistics per NR? What is the spatial resolution of results in Fig. 3?

 

Were all vegetation types represented in all provinces?

 

Section 3.3:

 

The manuscript reports differences in carbon density inside and outside NRs but lacks a statistical test (e.g., t-test or Mann–Whitney U test). Consider adding this to substantiate claims.

 

How were “outside NRs” defined? Was a buffer used, or were comparisons made across the same vegetation types regardless of protection status?

 

Were the initial conditions (e.g., forest density, degradation levels) comparable inside and outside the reserves in 2000? If not, this could bias carbon density comparisons.

 

Section 4.1

 

Be cautious in attributing increased C stocks solely to policy (e.g., SKFPs). While correlation is strong, causality would require more controlled comparisons or modeling.

Section 4.2 –

Statements about improved precipitation and reduced droughts are compelling. Consider including a simple climate variable trend graph to reinforce this point.

 

You mention the Grain for Green and TNSFP policies. Consider mapping C stock changes against these policy intervention zones to better demonstrate their impact.

 

When discussing fragmentation, a fragmentation index (e.g., edge-to-area ratio, patch density) would add technical depth.

 

Section 4.3

Clarify how the four types of protected areas in Fig. 7 were spatially delineated and compared (e.g., same vegetation types? Same time frame?).

 

Statistical comparison in Fig. 7:

 

Were differences between protection types statistically significant? If so, include p-values or confidence intervals in the figure or caption.

 

Add carbon sequestration (flux):

 

The focus is on carbon stocks. Did you also assess sequestration rates (fluxes)? Even indirect estimates (e.g., from NPP) could enrich the analysis.

 

Conclusion

The recommendation to improve plantation planning is sound, but could benefit from specific ecological zoning criteria (e.g., prioritize native species in buffer zones).

 

This sentence is grammatically awkward and technically unclear. Rephrase: e.g., “...this pattern was not observed in grassland ecosystems.”

 

Consider explicitly noting whether your results support adjusting the spatial allocation or classification of NRs under China's new ecological redline system.

Comments on the Quality of English Language

It needs lots of revision regarding the language!

Author Response

The reviewer 2:

This study assessed vegetation carbon (C) storage trends in China’s nature reserves (NRs) from 2000 to 2015 using NDVI data, revealing a 63.06% overall increase of 60.05% in forests and 86.33% in grasslands. Forest C density was higher inside NRs than outside, highlighting the important role of NRs in forest carbon conservation, despite limited impact on grassland carbon protection. I would recommend a minor revision for this paper.

 

Some spelling and grammar issues that authors need to check throughout the MS.

Some examples:

"polution" to "pollution"

R: Accepted

"enhance ecosystem resilience" should be "enhances" to match "also provides"

R: Accepted

"multi-variate" to "multivariate"

R: Accepted

“in this 15 years” to “over these 15 years”

R: Accepted

“so we obtained different regression models for different vegetation types”, reword to avoid repetition, e.g., “yielding distinct regression models per vegetation type

R: Accepted

Include an explicit study hypothesis or objective statement at the end of the Introduction

R: Accepted

Some major comments:

Section 3.2:

Quantification of "growth rate":

 

It's unclear whether "growth rate" refers to absolute changes in C stock, percent changes, or regression slope over time. Please clarify the metric and units.

R: Percent changes.

Uneven treatment of forest vs. grassland:

Forest C dynamics are described in more detail than grasslands. Consider balancing the narrative or explaining why grasslands receive less attention.

R: We tried to balance the equaled descriptions of both forests and grasses.

Clarify how spatial differences were calculated. Did you use grid-level NDVI changes within each NR, or aggregate statistics per NR? What is the spatial resolution of results in Fig. 3?

We aggregate the C mount at each NR, the spatial resolution of results is 250m in Fig. 3.

Were all vegetation types represented in all provinces?

R: Yes!

Section 3.3:

The manuscript reports differences in carbon density inside and outside NRs but lacks a statistical test (e.g., t-test or Mann–Whitney U test). Consider adding this to substantiate claims.

R: Yes! We used t-test.

 

How were “outside NRs” defined? Was a buffer used, or were comparisons made across the same vegetation types regardless of protection status?

R: We used the buffer belt as the outside NRs.

Were the initial conditions (e.g., forest density, degradation levels) comparable inside and outside the reserves in 2000? If not, this could bias carbon density comparisons.

R: We selected the similar vegetation between inside and outside the reserves.

 

Section 4.1

Be cautious in attributing increased C stocks solely to policy (e.g., SKFPs). While correlation is strong, causality would require more controlled comparisons or modeling.

R: We were carefully to this point. We thank the reviewer.

Section 4.2 –

Statements about improved precipitation and reduced droughts are compelling. Consider including a simple climate variable trend graph to reinforce this point.

R: We wanted to show some climatic factor changes, but the word limitation to such type article in this journal confines it.

You mention the Grain for Green and TNSFP policies. Consider mapping C stock changes against these policy intervention zones to better demonstrate their impact.

R: We wanted to show some climatic factor changes, but the word limitation to such type article in this journal confines it.

When discussing fragmentation, a fragmentation index (e.g., edge-to-area ratio, patch density) would add technical depth.

R: We wanted to show some climatic factor changes, but the word limitation to such type article in this journal confines them.

 

Section 4.3

Clarify how the four types of protected areas in Fig. 7 were spatially delineated and compared (e.g., same vegetation types? Same time frame?).

R: We have further explained them.

Statistical comparison in Fig. 7:

Were differences between protection types statistically significant? If so, include p-values or confidence intervals in the figure or caption.

R: Yes, They were statistically significant.

Add carbon sequestration (flux):

The focus is on carbon stocks. Did you also assess sequestration rates (fluxes)? Even indirect estimates (e.g., from NPP) could enrich the analysis.

R: Yes, We love to include this section, but it is a little bit long for the paper, we will try to resolute this in another manuscript.

Conclusion

The recommendation to improve plantation planning is sound, but could benefit from specific ecological zoning criteria (e.g., prioritize native species in buffer zones).

R: This great idea, we added it.

This sentence is grammatically awkward and technically unclear. Rephrase: e.g., “...this pattern was not observed in grassland ecosystems.”

R: Accepted, we try to rephrase them.

Consider explicitly noting whether your results support adjusting the spatial allocation or classification of NRs under China's new ecological redline system.

R: Accepted, We try to explained it.

Reviewer 3 Report

Comments and Suggestions for Authors

1. Expound more on introduction section.
2. Please thoroughly go through the paper to reduce the number of typos.
3. Could you please briefly write about the novelty of this work and briefly discuss about other similar works?
4. Is it possible to combine results and discussion together? It makes the explanation easier.
5. Datawise, quantification of C might be helpful.
6. What's the difference between forest C and grassland C?

Author Response

The Reviewer 3:

1. Expound more on introduction section.

R: We added some sentence to explain the aim of the paper.

2. Please thoroughly go through the paper to reduce the number of typos.

R: Accepted, We try to.

3. Could you please briefly write about the novelty of this work and briefly discuss about other similar works?

R: Accepted, We try to

4. Is it possible to combine results and discussion together? It makes the explanation easier.

R: Accepted, We try to

5. Datawise, quantification of C might be helpful.

R: Accepted.

6. What's the difference between forest C and grassland C?

R: The forest C is much more than Grassland Carbon, so the forest C was important than grassland C.

Reviewer 4 Report

Comments and Suggestions for Authors

The article deals with an important topic related to the dynamics of carbon storage in protected natural ecosystems of China in the period 2000–2015. The relevance of the study is questionable, as current global efforts to understand and mitigate the effects of climate change through land use management and forest conservation. Interest in natural carbon sinks and the role of nature reserves in climate regulation is growing every year. The use of NDVI data and spatial modeling contributes to the understanding of carbon dynamics on a large geographical scale. A large amount of work has been done by researchers, but the article lacks a clear presentation of what new ideas are offered in addition to the existing literature. Because similar works were carried out in different regions of individual countries. The methodology is acceptable in general, but it could be more detailed. For example, regression models and estimates of carbon stocks based on NDVI are insufficiently explained. Key information is missing, such as:

• What regression model was used?
• How was the coefficient obtained for carbon estimation?
• What is described in the analysis of uncertainty or the approach to verification.
• The influence of anthropogenic factors and climatic anomalies is mentioned, but neither analyzed nor quantified. Some sections (for example, Results and Discussions) are difficult to understand because of the lack of logical sequence. The abstract has no structure and should clearly summarize the background, objectives, methods, main findings and conclusions. Figures (for example, Figure 3) are presented without sufficient explanations or interpretations.

The quality of the English language is poor and requires serious editing by a native speaker or a professional editor.

Common problems include:

• Grammatical errors (verb tense, sentence structure)
• Clumsy or unclear wording
• Inconsistent usage terminology
• Plokhie transition offers

The quality of writing deteriorates scientific communication and should be significantly improved.

Along with my remarks, it is necessary to note the strengths of this article:

• An important and globally significant topic
• A large-scale dataset covering several types of ecosystems
• Appropriate use of the remote sensing and modeling approach

Recommendations for improvement

1. Thorough editing of the English manuscript.
2. Provide complete information about the methodology, including validation, regression statistics and justification of carbon coefficients.
3. Rewrite the annotation in a structured and informative format.
4. Clearly define the purpose and scientific contribution to introduction.
5. Add a section on research limitations and future directions.
6. More clearly discuss how this study differs from previous work or is based on it.

The article can be recommended for publication after eliminating the above

Remarks: improve writing in English, methodological clarity and scientific presentation

Comments for author File: Comments.pdf

Author Response

The reviewer 4:

The article deals with an important topic related to the dynamics of carbon storage in protected natural ecosystems of China in the period 2000–2015. The relevance of the study is questionable, as current global efforts to understand and mitigate the effects of climate change through land use management and forest conservation. Interest in natural carbon sinks and the role of nature reserves in climate regulation is growing every year. The use of NDVI data and spatial modeling contributes to the understanding of carbon dynamics on a large geographical scale. A large amount of work has been done by researchers, but the article lacks a clear presentation of what new ideas are offered in addition to the existing literature. Because similar works were carried out in different regions of individual countries. The methodology is acceptable in general, but it could be more detailed. For example, regression models and estimates of carbon stocks based on NDVI are insufficiently explained. Key information is missing, such as:

 

What regression model was used?

R: The multiple-regression model was used in the carbon estimations.

How was the coefficient obtained for carbon estimation?

R: We obtained NDVI for each site in whole China, and then we matched each plot biomass to each NDVI, and established the liner model, used the mode to extend the biomass for no plot area site. Please referred to Appendix 1 for model coefficient.

What is described in the analysis of uncertainty or the approach to verification.

R: We used 95% Confidence Interval as the uncertainty.

The influence of anthropogenic factors and climatic anomalies is mentioned, but neither analyzed nor quantified. Some sections (for example, Results and Discussions) are difficult to understand because of the lack of logical sequence. The abstract has no structure and should clearly summarize the background, objectives, methods, main findings and conclusions. Figures (for example, Figure 3) are presented without sufficient explanations or interpretations.

The quality of the English language is poor and requires serious editing by a native speaker or a professional editor.

R: We accepted the reviewer’s comments, and try to rephrase them.

Common problems include:

Grammatical errors (verb tense, sentence structure)

Clumsy or unclear wording

Inconsistent usage terminology

Plokhie transition offers

The quality of writing deteriorates scientific communication and should be significantly improved.

R: We accepted the reviewer’s comments, and try to rephrase them.

Along with my remarks, it is necessary to note the strengths of this article:

An important and globally significant topic

A large-scale dataset covering several types of ecosystems

Appropriate use of the remote sensing and modeling approach

Recommendations for improvement

R: We accepted the reviewer’s comments, and try to correct them.

Thorough editing of the English manuscript.

Provide complete information about the methodology, including validation, regression statistics and justification of carbon coefficients.

Rewrite the annotation in a structured and informative format.

Clearly define the purpose and scientific contribution to introduction.

Add a section on research limitations and future directions.

More clearly discuss how this study differs from previous work or is based on it.

The article can be recommended for publication after eliminating the above

R: Thanks! We accepted the reviewer’s comments, and try to improve them

Remarks: improve writing in English, methodological clarity and scientific presentation

R: We accepted the reviewer’s comments, and finished the rewriting.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Results from previous study should be included in the introduction section.

Is there a way to include more recent data? after 2015? at least up to 2024?

Author Response

Results from previous study should be included in the introduction section.

R6: We accepted the reviewer’s comments to include our previous study results close relatedly to this study in introduction.

Is there a way to include more recent data? after 2015? at least up to 2024?

R7: Our team attempted to source additional data points from the years 2015 to 2024.
Unfortunately, we encountered difficulties as these recent data were insufficient to establish a reliable correlation with NDVI. Despite our efforts, the available information did not meet the criteria necessary for inclusion in our analysis.    

Reviewer 4 Report

Comments and Suggestions for Authors

Peer Review Report

Title: Spatial Patterns and Temporal Variations of Carbon Storage in Forest and Grassland Ecosystems of China’s Nature Reserves

General Comments

            The revised manuscript demonstrates significant improvement over the initial submission. The authors have thoroughly addressed most of the previous reviewer’s comments, especially in terms of language clarity, scientific structure, and logical coherence. The manuscript is now more readable, the arguments are better supported by literature, and the conclusions are more impactful and clearly linked to the presented results.

            The study provides a comprehensive and valuable analysis of vegetation carbon storage trends in China's nature reserves (NRs) over a 15-year period, using NDVI-based modeling. The results contribute to a better understanding of the spatial and temporal dynamics of ecosystem carbon functions and offer practical recommendations for future nature reserve management in China.

Specific Comments

1. Language and Style

• The manuscript is now well-written in fluent academic English.
• Most grammatical issues and awkward phrasings have been corrected.
• However, several terms such as "vegetation carbon storage" and transition phrases like "This trend may be partly attributed to..." are repeated frequently. Minor variation in terminology and phrasing is recommended to enhance readability.

2. Scientific Content and Structure

• The authors now clearly state the research questions in the Introduction.
• The Discussion section is strengthened with additional literature citations and more nuanced interpretation of findings across different vegetation types.
• Regional differences in carbon storage patterns are now better contextualized with socio-economic and climatic factors.
• The added policy implications and recommendations in the Conclusion are relevant and well-aligned with the study’s findings.

3. Figures and Tables

• The figures are appropriate and the captions have improved.
• Table 1 contains useful comparisons, but the units (e.g., “0.03×10⁻²”) could be replaced with more intuitive formats like “Mg C/ha” for better clarity.
• Please double-check all table notations and legends for consistency and completeness.

4. Minor Issues to Correct

• In the Author’s name and affilation section, the corresponding author’s name is written as “Beijing Sang”, while elsewhere it appears correctly as “Beijia Sang”. Please correct this typographical error.
• Avoid excessive repetition of terms across consecutive sentences.
• Some sentences in the Discussion section remain slightly long and could be split for improved clarity.

Recommendation

Accept with Minor Revisions

The manuscript is scientifically sound, timely, and presents meaningful conclusions supported by robust data. Only minor editorial revisions remain to be addressed before final acceptance.

 

Comments for author File: Comments.pdf

Author Response

General Comments

The revised manuscript demonstrates significant improvement over the initial submission. The authors have thoroughly addressed most of the previous reviewer’s comments, especially in terms of language clarity, scientific structure, and logical coherence. The manuscript is now more readable, the arguments are better supported by literature, and the conclusions are more impactful and clearly linked to the presented results.

The study provides a comprehensive and valuable analysis of vegetation carbon storage trends in China's nature reserves (NRs) over a 15-year period, using NDVI- based modeling. The results contribute to a better understanding of the spatial and temporal dynamics of ecosystem carbon functions and offer practical recommendations for future nature reserve management in China.

R1: Thank you for your comments.

Specific Comments

1. Language and Style
   • The manuscript is now well-written in fluent academic
   • Most grammatical issues and awkward phrasings have been
   • However, several terms such as "vegetation carbon storage" and transition phrases like "This trend may be partly attributed .." are repeated frequently.

Minor variation in terminology and phrasing is recommended to enhance readability.

R2: We accepted the reviewer’s comments to try to reduce the repetitions and make them readability.

2.      Scientific Content and Structure

• The authors now clearly state the research questions in the
• The Discussion section is strengthened with additional literature citations and more nuanced interpretation of findings across different vegetation
• Regional differences in carbon storage patterns are now better contextualized with socio-economic and climatic factors.
• The added policy implications and recommendations in the Conclusion are relevant and well-aligned with the study’s

R3: Thank you for your comments

3.      Figures and Tables

• The figures are appropriate and the captions have
• Table 1 contains useful comparisons, but the units (e.g., “0.03×10⁻²”) could be replaced with more intuitive formats like “Mg C/ha” for better
• Please double-check all table notations and legends for consistency and

R4: Thank you for your comments. We have changed the units in table 1, so it is more clarity.

4.      Minor Issues to Correct

• In the Author’s name and affiliation section, the corresponding author’s name is written as “Beijing Sang”, while elsewhere it appears correctly as “Beijia Sang”.

Please correct this typographical error.

• Avoid excessive repetition of terms across consecutive
• Some sentences in the Discussion section remain slightly long and could be split for improved clarity.

R5: Thanks to the reviewer. We have changed the error and try to avoid repetition, and  some long sentences were shortened.

Recommendation

Accept with Minor Revisions

The manuscript is scientifically sound, timely, and presents meaningful conclusions supported by robust data. Only minor editorial revisions remain to be addressed before final acceptance.