Review Reports - Comparing the Carbon Storage Potential of Naturally Regenerated Tea Trees with Default New Zealand Carbon Look-Up Tables: A Case Study

Round 1

Reviewer 1 Report

"Comparing the carbon storage of twelve-year-old Leptosper- mum scoparium (manuka) with New Zealand default carbon look up tables: a case study" is a well drafted manuscript on the original problem. Manuscript is well written. So, it may be accepted after minor revision.

Author mentioned that "A comprehensive dataset pertaining to the carbon sequestration rates of primary colonisers in different regions is required". Is it also possible to count the carbon sequestration of microalgae in addition to the forests at the same time with the same tools?

Language clarity is worth needed in some sentences/statements..

Author Response

The authors thank the reviewer for their comments.

The carbon sequestration potential of microalgae had not been considered by the author. A different method with different tools would be required to quantify the carbon sequestration of microalgae. This study focuses on the above ground biomass carbon storage of naturally regenerated tea trees. A comment has been made on line 217 that quantification of microalgae carbon sequestration in such environments would help build a more complete picture of changes to carbon storage. A sentence has also been provided on Line 443 pertaining to the direction of future work.

Language clarity is worth needed in some sentences/statements..

Please be referred to changes made from errors identified by Reviewer 3.

Reviewer 2 Report

Overall, the paper demonstrates a strong structure and a persuasive argument that is supported by substantial evidence. It is both informative and well-written. Nonetheless, the discussion could benefit from more thorough explanations and expanded points in certain areas. To improve the discussion, the authors could consider providing more detail on the study methods, addressing potential limitations and biases, and exploring implications and future directions in greater depth. To enhance reader comprehension, additional background or contextual information on the topic may also be beneficial.

Title

1. To make the title more engaging and informative, I recommend considering alternative options that accurately reflect the study's focus and objectives. One such option is " The carbon storage potential of naturally regenerated tea trees: a case study"

Abstract

2. The abstract could be improved by providing clearer explanations of the study's objectives and findings.

Keywords

3. To provide more specificity and accuracy, I suggest using "New Zealand Emissions Trading Scheme" instead of "emissions trading scheme" as a keyword, as it highlights the geographical and regulatory context of the study. Additionally, "carbon storage" could be used as a single keyword to represent the combination of the two separate keywords.

Introduction

4. To improve the introduction, it is recommended to include a clear and concise statement of the research question or objective that encapsulates the main goal of the study.

Materials and Methods

5. Providing more details on the sampling grid used to select the five-meter by five-meter sampling sites would improve the study's methodological transparency and replicability.

6. Provide more details on how the circumference and diameter of stems were measured, including the precision of the instruments used.

7. Explain why the basal diameter method was chosen to estimate carbon stocks of all tea trees, regardless of height and DBH within plots.

8. Explain the reason for assuming a 50% carbon content of total dry matter in tea trees.

9. Provide more details on the comparison between the measured carbon dioxide sequestered by tea trees and that of twelve-year-old ‘Indigenous Forest’ in MPI’s look-up tables.

Results

10. The study only measured above-ground biomass, but other components of carbon storage, such as leaf litter and soil carbon fluxes, could also contribute to the carbon storage of the tea tree stands. Including these components in future studies would provide a more complete picture of carbon sequestration in the system.

11. The study notes that the growth of tea trees is likely stunted by the overarching exotic canopy. Future studies could consider how environmental factors, such as light levels and competition for resources, affect tea tree growth and carbon sequestration.

12. Understanding the cause of the bimodality could help improve the accuracy of carbon storage estimates for tea tree stands.

Discussion

13. 4.1. Inclusion of unvegetated land – the statement that "collected tea tree carbon storage data greatly differs from that described by MPI (+81.80%)" could benefit from further elaboration on the reasons for the discrepancy, such as differences in methodology or assumptions. Additionally, the discussion could be strengthened by exploring potential implications of the findings, such as the need for more accurate carbon storage estimates and the importance of considering the impact of establishment factors on woody vegetation. The argument regarding hill country land being unforested or grazed could also be further developed to provide a more nuanced understanding of the factors influencing vegetation establishment and carbon storage. Providing additional sources and data to support the claims made would also strengthen the discussion.

14. 4.2. Bimodal distribution – This section of the discussion could be improved by providing more context and explanation for the bimodal distribution of total carbon storage among sample sites. The authors could discuss the implications of this distribution for accurately estimating carbon storage in naturally regenerated tea tree stands, as well as for making policy decisions related to carbon sequestration. Additionally, the authors could provide more information on the limitations of their study design and how these limitations may have affected their results.

15. 4.3. Potential sources of bias – The authors could discuss the potential impact of this bias on the accuracy of modelled carbon storage and suggest ways to mitigate this bias in future studies. The authors could also provide more information on the inaccessible sample site locations and how these areas may have affected the overall results. The authors could further elaborate on how the statistical weighting of tea trees over a height of one metre could have impacted the statistical relationship between the three variables and carbon storage. They could discuss the potential implications of this weighting on the overall results and suggest ways to address this issue in future studies. The discussion could also benefit from a more detailed consideration of other potential sources of bias that may have affected the results. For example, the authors could discuss the potential impact of sample size and variability in sample site selection on the overall results, and suggest ways to address these issues in future studies.

16. 4.4. Review of indigenous forestry category on MPI look-up tables - More specific recommendations for future research could be provided. It would be helpful to provide more information on the MPI look-up tables, such as what they are used for and how they are developed. The discussion could benefit from more detailed explanations of the factors that contribute to differences in carbon sequestration potential between different tree species and regions.

17. The conclusions could be improved by summarizing the main findings of the study more explicitly. The conclusions could also be strengthened by acknowledging any limitations of the study and suggesting areas for further research to address these limitations.

Author Response

The authors thank the reviewer for their comments.

Title

To make the title more engaging and informative, I recommend considering alternative options that accurately reflect the study's focus and objectives. One such option is " The carbon storage potential of naturally regenerated tea trees: a case study"

The authors agree the Title could be improved to better reflect the focus and objectives of the paper. However, comparing look-up tables to the carbon storage potential of naturally regenerating tea trees is the key objective of the paper. The title has subsequently been modified to read “Comparing the carbon storage potential of naturally regenerated tea trees with default New Zealand carbon look-up tables: a case study”.

Abstract

The abstract could be improved by providing clearer explanations of the study's objectives and findings.

The authors agree that this could be clearer. Two sentences have been added to the abstract, one detailing the aim of the study (Line 14) and one elaborating on the study’s findings (Line 19).

Keywords

To provide more specificity and accuracy, I suggest using "New Zealand Emissions Trading Scheme" instead of "emissions trading scheme" as a keyword, as it highlights the geographical and regulatory context of the study. Additionally, "carbon storage" could be used as a single keyword to represent the combination of the two separate keywords.

The authors agree. “emissions trading scheme” has become “New Zealand Emissions Trading Scheme”. “carbon” and “storage” has become “carbon storage”.

Introduction

To improve the introduction, it is recommended to include a clear and concise statement of the research question or objective that encapsulates the main goal of the study.

Please refer to the last paragraph in the introduction. More specifically Line 90 which reads “The objective of this was to highlight the difference in carbon storage between tea trees and default carbon look-up tables for naturally regenerating land”. In addition in Line 60 readers are made aware of the link to the look tables in [15].

Materials and Methods

Providing more details on the sampling grid used to select the five-meter by five-meter sampling sites would improve the study's methodological transparency and replicability.

The authors agree. A sentence detailing the specific tool (Create Fishnet tool) and input features (polygon) has been included (Line 150).

Provide more details on how the circumference and diameter of stems were measured, including the precision of the instruments used.

The authors agree. The precision of the instruments used have been included on Line 185.

Explain why the basal diameter method was chosen to estimate carbon stocks of all tea trees, regardless of height and DBH within plots.

Please refer to Line 196. Basal diameter and height are the two key variables used in the allometric equations derived by Beets et al. (2014)

Explain the reason for assuming a 50% carbon content of total dry matter in tea trees.

The authors agree. A sentence detailing this decision has been added on Line 224.

Provide more details on the comparison between the measured carbon dioxide sequestered by tea trees and that of twelve-year-old ‘Indigenous Forest’ in MPI’s look-up tables.

The authors agree. A statement quantifying the carbon storage of twelve year old ‘Indigenous Forest” has been included on Line 232.

Results

The study only measured above-ground biomass, but other components of carbon storage, such as leaf litter and soil carbon fluxes, could also contribute to the carbon storage of the tea tree stands. Including these components in future studies would provide a more complete picture of carbon sequestration in the system.

The authors agree. A sentence has been added to the conclusion in regards to the direction of future work on Line 443.

The study notes that the growth of tea trees is likely stunted by the overarching exotic canopy. Future studies could consider how environmental factors, such as light levels and competition for resources, affect tea tree growth and carbon sequestration.

The authors agree. A comment has been added to the conclusion in regards to the direction of future work on Line 443.

Understanding the cause of the bimodality could help improve the accuracy of carbon storage estimates for tea tree stands.

The authors agree. Please be referred to changes made to the discussion as detailed below.

Discussion

4.1. Inclusion of unvegetated land – the statement that "collected tea tree carbon storage data greatly differs from that described by MPI (+81.80%)" could benefit from further elaboration on the reasons for the discrepancy, such as differences in methodology or assumptions. Additionally, the discussion could be strengthened by exploring potential implications of the findings, such as the need for more accurate carbon storage estimates and the importance of considering the impact of establishment factors on woody vegetation. The argument regarding hill country land being unforested or grazed could also be further developed to provide a more nuanced understanding of the factors influencing vegetation establishment and carbon storage. Providing additional sources and data to support the claims made would also strengthen the discussion.

The authors agree. A sentence has been included on Line 339 offering a reason for the observed differences (methods of study vs methods of look-up tables), with a reference. A statement has been made on Line 418, elaborating on the conservative nature of the carbon look-up tables. A sentence has been included on Line 432 detailing the implications of a species specific dataset.

4.2. Bimodal distribution – This section of the discussion could be improved by providing more context and explanation for the bimodal distribution of total carbon storage among sample sites. The authors could discuss the implications of this distribution for accurately estimating carbon storage in naturally regenerated tea tree stands, as well as for making policy decisions related to carbon sequestration. Additionally, the authors could provide more information on the limitations of their study design and how these limitations may have affected their results.

The authors agree. Three sentences providing extra context for the bimodal distribution has been added on Line 359. A sentence providing information on the potential impacts of a dataset that addresses the bimodality of the authors data is included on Line 384. The authors feel that the limited scope of the study has been well communicated. Specifically, in the introduction (Line 94), discussion (Line 414) and conclusion (Line 439).

4.3. Potential sources of bias – The authors could discuss the potential impact of this bias on the accuracy of modelled carbon storage and suggest ways to mitigate this bias in future studies. The authors could also provide more information on the inaccessible sample site locations and how these areas may have affected the overall results. The authors could further elaborate on how the statistical weighting of tea trees over a height of one metre could have impacted the statistical relationship between the three variables and carbon storage. They could discuss the potential implications of this weighting on the overall results and suggest ways to address this issue in future studies. The discussion could also benefit from a more detailed consideration of other potential sources of bias that may have affected the results. For example, the authors could discuss the potential impact of sample size and variability in sample site selection on the overall results, and suggest ways to address these issues in future studies.

The authors agree. A suggestion has been made for future studies in regard to measuring height on Line 395. A suggestion has been made for future studies in regard to statistical weighting of trees on Line 407. The authors feel that the limited scope of the study has been well communicated. Specifically, in the introduction (Line 94), discussion (Line 414) and conclusion (Line 439).

4.4. Review of indigenous forestry category on MPI look-up tables - More specific recommendations for future research could be provided. It would be helpful to provide more information on the MPI look-up tables, such as what they are used for and how they are developed. The discussion could benefit from more detailed explanations of the factors that contribute to differences in carbon sequestration potential between different tree species and regions.

The authors agree. Please see the inclusion of the sentence on Line 418. Further context on the MPI carbon look-up tables have been provided on Line 339. A statement detailing how factors impact carbon sequestration is included on Line 427.

The conclusions could be improved by summarizing the main findings of the study more explicitly. The conclusions could also be strengthened by acknowledging any limitations of the study and suggesting areas for further research to address these limitations.

The authors agree. Sentences pertaining to the direction of future work have been on Line 443. The authors feel that the limited scope of the study has been well communicated. Specifically, in the introduction (Line 94), discussion (Line 414) and conclusion (Line 439).

Reviewer 3 Report

The manuscript deals with an issue that is gaining importance and recognition due to climate change and the need to mitigate carbon emissions. It deals with a specific case in New Zealand but can be relevant to other regions of the world seeking to establish a fair and equitable compensation scheme for carbon capture and sequestration. The paper is well written and organized and can be published with minimal corrections (spelling, punctuation).

Comments for author File: Comments.pdf

Author Response

The authors thank the reviewer for their comments. All spelling and punctuation corrections suggested as per the attached pdf file have been implemented. Specifically, amendments to line 30, 89, 95, 106, 127, 129 and 234. A further proof read was conducted resulting in the following: ‘indigenous forest’ has been capitalised on lines 84 and 85. An extra space has been deleted on line 17. ‘as’ has been replaced by ‘has’ on line 33. ‘which’ has been added to line 87. ‘a’ has been added to line 128. ‘sp’ deleted from line 129. Spelling of ‘Leptospermum’ has been corrected on lines 23, 136, 137, 193 and 253. Spelling of ‘scoparium’ has been corrected on line 193 and 253. Spelling of ‘Kunzea’ has been corrected on lines 24, 83, 141 and 193. ‘and Kunzea ericoides’ has been removed from line 213 to better represent referenced material. Spelling of ‘destructively’ has been corrected on line 391.

Round 2

Reviewer 2 Report

Thank you for your thorough and thoughtful response to my comments. I appreciate the effort you have put into addressing the concerns raised and improving the manuscript accordingly. The revisions you have made, including elaborating on certain points, providing additional context, and making suggestions for future research, have significantly strengthened the paper. I am pleased with the changes made to the title, abstract, and keywords, as they now more accurately reflect the study's focus and objectives. Additionally, the added details in the Materials and Methods section have improved the study's methodological transparency and replicability. The revisions to the Results and Discussion sections provide a more comprehensive understanding of the study's findings, their implications, and potential limitations. The acknowledgement of these limitations and suggestions for future research are valuable for guiding further work in this area. I believe the manuscript has been substantially improved and, as a result, is now better suited for publication. I appreciate your attention to detail and dedication to enhancing the quality of the paper. I look forward to seeing this work published and contributing to the broader scientific conversation on carbon storage potential and carbon look-up tables.