Assessing Carbon Sequestration Potential in State-Owned Plantation Forests in China and Exploring Feasibility for Carbon Offset Projects

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The current investigation entitled “Assessing Carbon Sequestration Potential in State-Owned Plantation Forests in China and Exploring Feasibility for Carbon Offset Projects” authored by Chen et al.  quantified the carbon sink potential and average annual carbon sequestration of existing state-owned plantation forests. Simultaneously, authors also analysed the carbon offsetting capacity of the existing state-owned plantation forests; and proposed a strategy for the development of China's future forestry carbon offsetting projects.

Comment/Suggestions

The abstract section is well written covering all the aspect. I have only two doubts (i) in line 21, should the unit not be CO2 equivalent?? (ii) in Line 22 what does the hm2.a signifies???

In line 35-36. The statement should be revised as follow “…as a significant approach to reduce greenhouse gas emissions and accomplish Nationally Determined Contributions (NDCs)”. As per the statement provided in line 37-, I want clarify that generally State-owned forests already accumulated enough biomass and offsets only can be generated if the addition of the biomass can be done from the baseline. This should be considered by authors and mentioned in the manuscript for better clarity to the readers. However, conditions for the CCER should be something else. What at least authors need to specify it.

Line 64-65. I don’t think authors need to provide too old references. Moreover, the referencing style need to be revised as per the Journal’s guidelines. Overall, the introduction section have enough background information but the research gap of the current investigation need to be properly indicated.

In the materials and methods, the first sub section should be the detail regarding the study area. Moreover, the equations provided in the material and method section should be supplemented with the relevant references from which it is adopted.

Table 1 can be provided in the supplementary files. Section 2.5.2. it should be Forest CO2 mitigation rathe than carbon sequestration, since carbon sink is multiplied by 3.67 (44/12). Kindly check it.

In material and method section, I suggest authors to add the information regarding the statistical technique applied in the current investigation.

Line 174-181, this should be the part of the study area information rather than provided at the end of the material and methods section. The title of the subsection 3.1 need to be revised and should be limited to Carbon stock and density. Line 187-188. There is no need of this statement. The placement of the figure 1 is not correct. Figure 1 is too clumsy and can be split into 2 or more for better readability. Similarly follow it for the figure 2

Line 235-236., need to be removed. Line 251 and several other places the author have indicated significant difference or non-significant differences. However, the author did not applied any statistical test to test the significance level. Kindly justify. Subsection 4.2, the calculation Bias analysis should be the part of the result section. Moreover, Title should revied to Bia analysis only. The discussion section needs to be further strengthened by recent literature. Moreover, the conclusion section needs to be revised and should be limited to the constructive conclusive statement with way forward and limitation of the current investigation.

Overall, the manuscript have novelty and well within the scope of the Journal but need major revision.

 

Regards

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

Dear reviewer:

Thank you for reviewing this manuscript. Your comments have greatly helped us improve the quality of the thesis. We have responded to each of your questions individually. Your feedback primarily focused on the structure of the article, the quality of the images, the content descriptions, and detailed questions regarding the literature. We have made revisions within the limited time available, which may still be insufficient, but we hope you will find them satisfactory.

 

Comment 1:

The abstract section is well written covering all the aspect. I have only two doubts (i) in line 21, should the unit not be CO₂ equivalent?? (ii) in Line 22 what does the hm²·a signifies???

I agree that using "CO₂ equivalent" or "CO₂e" would be more precise and encompassing. I will revise the manuscript to use "CO₂e" to ensure clarity and accuracy in representing the greenhouse gas measurements.

In line 22, tCO₂/(hm²·a) is used to denote “hectares per year “. To improve clarity, I proposed to amend the text to explicitly state 1.41 tonnes of CO₂ per hectare per year.

 

Comment 2:

2.In line 35-36. The statement should be revised as follow “…as a significant approach to reduce greenhouse gas emissions and accomplish Nationally Determined Contributions (NDCs)”. As per the statement provided in line 37-, I want clarify that generally State-owned forests already accumulated enough biomass and offsets only can be generated if the addition of the biomass can be done from the baseline. This should be considered by authors and mentioned in the manuscript for better clarity to the readers. However, conditions for the CCER should be something else.

I have revised it in lines 35-36 (Grammatical errors) and lines 41-45 (added notes on baseline and additionality).

Lines 41-45:

These credits are a means to offset the carbon footprint of businesses and individuals. It is important to note that while forests often contain significant biomass, the generation of carbon credits primarily relies on the addition of carbon sequestration beyond a predetermined baseline, such as forest preservation and improved forest management that provide additional carbon sequestration benefits relative to a business-as-usual scenario (Austin et al., 2020[1]; Rossi et al., 2023[2]; Broekhoff et al., 2019[3],). As per available data (Ecosystem Marketplace, 2022), the issuance of forestry carbon credits within the international carbon market experienced consistent growth, averaging an annual increase of 64% from 2010 to 2015.

Comment 3:

Line 64-65. I don’t think authors need to provide too old references. Moreover, the referencing style need to be revised as per the Journal’s guidelines. Overall, the introduction section have enough background information but the research gap of the current investigation need to be properly indicated.

The reason we conducted a brief literature review through old references is that the current methods used to quantify carbon sinks have matured, so we felt it was important to retain this brief section. Also, through the literature review, we provide an additional description of the research gap in lines 93-97.

Lines 93-97:

Due to the review of previous studies and the quantification methods of forest carbon sinks in China, it is apparent that current research primarily focuses on quantifying the carbon sinks at the ecological level and determining how much carbon emissions can be neutralized. Therefore, considering the characteristics of the state-owned plantation forests mentioned above, a quantitative study is necessary.

Comment 4:

In the materials and methods, the first sub section should be the detail regarding the study area. Moreover, the equations provided in the material and method section should be supplemented with the relevant references from which it is adopted.

We have added a section regarding the study area.

We have added reference to the equations in the materials section.

Comment 5:

Table 1 can be provided in the supplementary files. Section 2.5.2. it should be Forest CO2 mitigation rathe than carbon sequestration since carbon sink is multiplied by 3.67 (44/12). Kindly check it.

We have moved Table 1 to the supplementary files.

We have changed the title of 2.5.2.

 

Comment 6:

In material and method section, I suggest authors to add the information regarding the statistical technique applied in the current investigation.

We completed the methodology section by adding the software and information on R-squared, Adjusted R-squared, and Root Mean Square Deviation

 

Comment 7:

Line 174-181, this should be the part of the study area information rather than provided at the end of the material and methods section. The title of the subsection 3.1 need to be revised and should be limited to Carbon stock and density. Line 187-188. There is no need of this statement. The placement of the figure 1 is not correct. Figure 1 is too clumsy and can be split into 2 or more for better readability. Similarly follow it for the figure 2

We have moved lines 174-181 to the study area section to provide additional context.

We have changed the title of subsection 3.1 to 'Carbon Stock and Density in State-Owned Plantation Forests in China'.

We split Figure 2 into two graphs, which made it more visually appealing and easier to understand. However, our attempts to divide Figure 1 into several graphs resulted in each segment becoming too sparse, making it difficult to discern the relationships between the different bars. Therefore, we keep Figure 1 as originally presented.

Comment 8:

Line 235-236., need to be removed. Line 251 and several other places the author have indicated significant difference or non-significant differences. However, the author did not applied any statistical test to test the significance level. Kindly justify. Subsection 4.2, the calculation Bias analysis Sshould be the part of the result section. Moreover, Title should revied to Bia analysis only. The discussion section needs to be further strengthened by recent literature. Moreover, the conclusion section needs to be revised and should be limited to the constructive conclusive statement with way forward and limitation of the current investigation.

We have removed Line 235-236. Line 251 and similar descriptions attempt to compare carbon sinks with current carbon stock levels to assess if areas with higher carbon stock levels also have greater potential for carbon sinks. No special statistical methods are employed.

We have moved the 'Bias analysis' section to the results part.

We provide additional descriptions of the biodiversity as well as the REDD+ baseline, with citations to the literature.

We rewrite the conclusion. We first describe the results of the study on the insufficient carbon offsetting capacity of existing state-owned plantation forests in China and then outline strategies for future development. Additionally, we have added a chapter on research limitations.

 

We sincerely hope this manuscript will be finally meet your requirements and acceptable to be published. Thank you very much for all your help.

Zheng Chen, Buddhi Dayananda, Huaqiang Du, Guomo Zhou and Guangyu Wang

 

[1] Austin, K. G., Baker, J. S., Sohngen, B. L., Wade, C. M., Daigneault, A., Ohrel, S. B., ... & Bean, A. 2020. The economic costs of planting, preserving, and managing the world’s forests to mitigate climate change. Nature communications, 11(1), 5946. https://doi.org/10.1038/s41467-020-19578-z

[2] Rossi, D. J., Baker, J. S., & Abt, R. C. 2023. Quantifying additionality thresholds for forest carbon offsets in Mississippi pine pulpwood markets. Forest Policy and Economics, 156, 103059. https://doi.org/10.1016/j.forpol.2023.103059

[3] Broekhoff, D., Gillenwater, M., Colbert-Sangree, T., and Cage, P. 2019. “Securing Climate Benefit: A Guide to Using Carbon Offsets.” Stockholm Environment Institute & Greenhouse Gas Management Institute. https://www.offsetguide.org/pdf-download/

Reviewer 2 Report

Comments and Suggestions for Authors

This paper is dealed to regional and whole country evaluation of carbon units and carbon offsets in such a big country as China. The article uses mainly generalized methods and calculation methods to determine the carbon capacity of ecosystems composed of different tree species. This raises the issue that monospecific woody plant communities are used for calculations. And how to calculate multi-species communities? Because in nature forest communities are rarely monospecific. In general, the article is not in the field of classical forest ecology and belongs in this sense within the framework of green ecology. Therefore, it is necessary to indicate in the introduction why the article is intended for this journal. 

detailed comments:

table 1 - why one plant are nemed on the level of genera and other - on the level of species. this is a forests journal, thus, authors have to follow to traditionsl botanical rules.

materials and methods chapter: why you started from describtion of calculation methodology? I prefer to see metohdology of obtaining of primary data - how belowground biomass was evaluated in field? the same for abovegroung biomass and other features.

there are few references in chapter 2.7 - but there is no idea about data quality and presigion.

what was the methodology of prediction in the chapter 3.3? is it possible to use some mashine learning?

I reccomend to cite more paper on the carbon offsets in countrie, adjaicent to China. E.g. recently many papers has been published in Russia on this topic, especially on the carbon offsents, units and methodology.

On the whole, the material presented is good and of high quality, which deserves to be published after making appropriate edits.

 

Author Response

Dear reviewer:

Thank you for reviewing this paper. Your comments have greatly helped us improve the quality of the thesis. We have responded to your questions individually. Generally, your comments mainly focus on the data and methods used. We calculated the carbon sink of state-owned plantation forests on a national scale. Therefore, to select land under state-owned forest tenure, we used the national forest inventory data, which is non-spatial and does not allow for consideration of mixed forest situations. Similarly, some of the dominant species in this dataset are only identified at the genus level, which is significant and cannot be ignored, leading to varying levels of description. Overall, these data limitations affect both the results and the reading experience, but they seem unavoidable. To address this issue, we have added a “Limitation”.

We have made revisions within the limited time available, which may still be insufficient, but we hope you will find them satisfactory.

 

 

Comments 1:

This paper is dealed to regional and whole country evaluation of carbon units and carbon offsets in such a big country as China. The article uses mainly generalized methods and calculation methods to determine the carbon capacity of ecosystems composed of different tree species. This raises the issue that monospecific woody plant communities are used for calculations. And how to calculate multi-species communities? Because in nature forest communities are rarely monospecific. In general, the article is not in the field of classical forest ecology and belongs in this sense within the framework of green ecology. Therefore, it is necessary to indicate in the introduction why the article is intended for this journal.

 

We used the National Forest Inventory dataset to fit logistic growth curves. In this database, parameters such as stocking density are categorized by single tree species. Since this database lacks spatial data, it cannot distinguish mixed forests. Moreover, the research focuses on state-owned plantation forests, making it difficult to determine tree species origin and ownership with spatial data. Overall, due to these data limitations, considering planting patterns under normal circumstances is virtually impossible, representing a shortcoming of this paper.

 

Comments 2:

table 1 - why one plant are named on the level of genera and other - on the level of species. this is a forests journal, thus, authors have to follow to traditional botanical rules.

As mentioned in comment 1, the China Forest Inventory dataset has some limitations, primarily because it lacks spatial data, making it challenging to delineate specific dominant tree species. For instance, in this paper, some species are only identified up to the genus level. While remote sensing could offer greater accuracy in identifying tree species, it faces difficulties in separating ownership. These inherent limitations are unavoidable. However, I believe that if national-scale spatial boundaries based on ownership are established in the future, the use of remote sensing data will become more accurate.

Comments 3:

materials and methods chapter: why you started from description of calculation methodology? I prefer to see methodology of obtaining of primary data - how belowground biomass was evaluated in field? the same for aboveground biomass and other features.

This study is conducted on a national scale using publicly available inventory data, not data from sample plots. In the actual development of forestry carbon sink projects, the formulas for calculating above-ground biomass are reviewed from previous literature or derived from field measurements of tree height and diameter at breast height (DBH) to calculate storage volume. Below-ground biomass is calculated using the root-stem ratio found in regional-level greenhouse gas inventories. Other carbon pools are generally not calculated due to the costs of investigation and monitoring, as the volume of these carbon sinks is not large.

In this paper, due to the extensive scale, aboveground biomass was calculated by fitting growth equations to the required data. Belowground biomass was calculated using the root-stem ratio, and other carbon pools were estimated using default values.

Comments4:

there are few references in chapter 2.7 - but there is no idea about data quality and presigion.

We have added more detail about data quality, such as the number of sample plots and types of data.

 

Comment5

what was the methodology of prediction in the chapter 3.3? is it possible to use some machine learning?

We used logistic growth curve models to predict carbon stock, then used Equation (6) to calculate the carbon sink. Machine learning and simulation functions could also predict carbon stock and carbon sink. However, the same tree in different areas has different carbon sequestration capacities. Therefore, if we use machine learning, we need enough samples to train the neural network effectivel, i.e., the same tree species may be trained up to seven times. our research utilized National Inventory data, which did not include a sufficiently large sample to train a stable neural network. Consequently, we did not use machine learning to predict carbon sinks.

Comment6

I recommend to cite more paper on the carbon offsets in countries, adjacent to China. E.g. recently many papers has been published in Russia on this topic, especially on the carbon offsets, units and methodology.

Thanks to your suggestion, we have added some literature on carbon offsets and biodiversity and REDD+ baseline design to increase the readability of the article.

 

We sincerely hope this manuscript will be finally meet your requirements and acceptable to be published. Thank you very much for all your help.

Zheng Chen, Buddhi Dayananda, Huaqiang Du, Guomo Zhou and Guangyu Wang

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

In the first round of revision, the authors have made considerable corrections in the manuscript. However, there are still several minor revisions which authors need to be taken care off:

Line 94. “Due to the review of previous studies and the quantification methods of forest carbon 94 sinks in China,” need t be revised. The meaning is not clear.

In subsection, I suggest authors to  kindly climatic and topographical detail about the study area.

In Subs section 2.2-2.7. There is no need to write “calculation of” this should be removed.

In the title of subsections of result, there is no need to write “in Existing State-owned Plantation Forests in China” since it is already well established that the research was conducted in these forests.

So kindly change the title of the subsections such as 3.1 Carbon Stock and Carbon Density and so on for others also.

Discussion still need to be strengthen in the light of previous literature; it is still lacking in the manuscript.

 

Subsection 4.2 it should not be the part of the discussion section but the part of the Policy initiatives and other some other suitable title. Limitations of the current investigation should be merged with the conclusion section of the manuscript. 

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Dear reviewer:

Thank you for your comments. We have made changes to the introduction section, and the comment does improve the flow of the article.

Comment 1:

Line 94. “Due to the review of previous studies and the quantification methods of forest carbon sinks in China,” need t be revised. The meaning is not clear.

Thank you for your comment. We have made changes to the introduction section, and the comment indeed improves the flow of the article. Here is the revised version:

Given the extensive research and diverse methodologies applied to quantify forest carbon sinks in China, it is evident that most studies focus on ecological-level carbon quantification and its potential to neutralize carbon emissions. These studies encompass all natural and planted forests and do not specifically quantify forest stands that could be developed for forestry carbon offset projects. Therefore, considering the importance of state-owned forests in carbon offset projects in China, a quantitative study is necessary.

 

Comment 2:

In subsection, I suggest authors to kindly climatic and topographical detail about the study area.

We have added more details.

 

Comment 3:

In Subs section 2.2-2.7. There is no need to write “calculation of” this should be removed.

We have removed “calculation”

 

Comment 4:

In the title of subsections of result, there is no need to write “in Existing State-owned Plantation Forests in China” since it is already well established that the research was conducted in these forests.

We have removed ‘in Existing State-owned Plantation Forests in China’.

 

Comment 5:

So kindly change the title of the subsections such as 3.1 Carbon Stock and Carbon Density and so on for others also.

We have changed the title.

 

Comment 6:

Discussion still need to be strengthen in the light of previous literature; it is still lacking in the manuscript.

 We have added more details in 4.1.

 

Comment 7:

Subsection 4.2 it should not be the part of the discussion section but the part of the Policy initiatives and other some other suitable title. Limitations of the current investigation should be merged with the conclusion section of the manuscript. 

We have changed the title and moved the position.

We have put the limitations and conclusions sections together.

Thank you very much for all your help.

Zheng Chen, Buddhi Dayananda, Huaqiang Du, Guomo Zhou and Guangyu Wang