Characteristics of Biomass and Carbon Stocks Accumulation and Biomass Estimation Model in Kandelia obovata Mangroves at the Northern Edge of Its Distribution in China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is an interesting manuscript, which falls within the scope of forests. I do have some minor comments, which can improve the readability of the manuscript:

- At the start of the abstract, please describe the overall context and why this research is useful (e.g. a summary of lines 51-56). 

- L24-26: Consider also mentioning absolute values, rather than only relative values as %

-L42 - 45: When mentioning the carbon sequestration potential, do you mean both below- and aboveground? Can you be more specific here? Even though the focus of the manuscript lies on aboveground biomass and carbon storage, it might be good to address belowground storage as well (in the Introduction and/or Discussion). A general idea (based on literature) can help to further interpret the aboveground storage potential.

-L77-84: In my opinion, several remote sensing techniques are also useful as biomass estimation method. This is currently lacking here.

- L121: How was plot size determined? Based on literature?

- L126: How were roots collected? Please specify this here as well.

-L131: Which method was used to determine the carbon content of each component?

- L274 - 280: Consider moving this section to the Discussion, or integrate with L312 - 316.

- Discussion: As mentioned before, it might be relevant to extend the current discussion and also take into account soil carbon storage and remote sensing techniques to provide more/other perspective(s)

Author Response

Comments 1:[ At the start of the abstract, please describe the overall context and why this research is useful (e.g. a summary of lines 51-56). ]

Response 1:[ A comprehensive description of the overall background and the significance of the research has been incorporated.]

Comments 2:[L24-26: Consider also mentioning absolute values, rather than only relative values as %]

Response 2:[ The following content has been added: The total biomass ranged from 0.100 to 0.925 Mg ha⁻¹, while the carbon stocks ranged from 0.038 to 0.377 Mg C ha⁻¹]

Comments 3:[L42 - 45: When mentioning the carbon sequestration potential, do you mean both below- and aboveground? Can you be more specific here? Even though the focus of the manuscript lies on aboveground biomass and carbon storage, it might be good to address belowground storage as well (in the Introduction and/or Discussion). A general idea (based on literature) can help to further interpret the aboveground storage potential.]

Response 3:[ When referring to the carbon sequestration potential in the context of the mangrove ecosystem, it encompasses both below - and aboveground components. The biomass aboveground, such as the trunks, branches, and leaves of mangrove trees, contributes significantly to carbon sequestration through photosynthesis, storing carbon dioxide in the form of organic matter. Simultaneously, the belowground biomass, including the extensive root systems of mangroves, also plays a crucial role. Mangrove roots can not only store carbon in the soil but also enhance soil stability, which in turn helps in long - term carbon sequestration. Therefore, when considering the carbon sequestration potential of the mangrove ecosystem, both above and belowground aspects are integral and cannot be overlooked.]

Comments 4:[ L77-84: In my opinion, several remote sensing techniques are also useful as biomass estimation method. This is currently lacking here.]

Response 4:[ I agree you and have improved the related content]

Comments 5:[ L121: How was plot size determined? Based on literature?]

Response 5:[ Based on literature and fieldwork. The fact that mangroves in the investigated plots are identified as shrubs and small trees is a crucial factor. Generally, shrubs and small trees have a relatively smaller canopy spread and root system compared to large trees.  A plot size of 5×10m is likely adequate to include a representative sample of these mangrove individuals, along with their associated understory and soil conditions. This size can capture the primary ecological interactions and characteristics of the mangrove community at the shrub and small - tree stage.]

Comments 6:[ L126: How were roots collected? Please specify this here as well.]

Response 6:[ Root biomass was obtained via full excavation. Roots were carefully extracted from adjacent soil by surface - to - depth digging, then weighed.]

Comments 7:[ L131: Which method was used to determine the carbon content of each component?]

Response 7:[ Potassium dichromate oxidation method. Under heating conditions, the carbon in plant samples is oxidized by an excess of potassium dichromate - sulfuric acid solution.  Subsequently, the remaining potassium dichromate is back - titrated with ferrous sulfate standard solution, and the carbon content of plant samples is calculated according to the amount of consumed potassium dichromate.]

Comment 8: [-L274-280: Consider moving this section to the discussion board, or merging it with L312-316.

Response 8: [I agree. Relevant parts have been merged]

Comment 9: [Discussion: As mentioned earlier, it may be relevant to extend the current discussion and consider soil carbon storage and remote sensing techniques to provide more/other perspectives]

Reply 9: [Relevant content has been improved.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript (forests-3472957) presents the biomass distribution of Kandelia obovata in Zhejiang, China, and develops regression models to estimate its biomass using tree parameters such as basal diameter and height. The optimal model (R² = 0.908) demonstrates that combined variables (DH, D²H) enhance accuracy, providing a reliable tool for biomass estimation in mangrove plantations at the northern limit of the species' range. The introduction, materials and methods, and parts of the results section are adequate in the manuscript. However, the figures and their captions require revision. For example, all elements and colours appearing in the figures must be explicitly described and explained in the captions. The reader should be able to understand the content of the figure solely by referring to the caption, which is not currently the case. Furthermore, both the tables and figures must include relevant comparative statistical analyses appropriate to the different treatments presented. Please review these carefully and revise the figures and tables accordingly, incorporating the necessary statistical analyses. The discussion section needs to be expanded to highlight the key points and counterpoints in comparison with the existing literature. Additionally, the authors must clarify whether the objectives and hypotheses presented at the beginning of the study were confirmed or refuted. The discussion should also include future perspectives, the main limitations of the study, and possible research directions. The conclusions should be rewritten to emphasise the manuscript’s primary contribution. Furthermore, the references need to be reviewed, as many are outdated; they should be replaced with more recent and relevant sources.

Comments on the Quality of English Language

Some paragraphs contain redundant information and should be revised for conciseness. 

Author Response

Comments 1:[ At the start of the abstract, please describe the overall context and why this research is useful (e.g. a summary of lines 51-56). ]

Response 1:[ A comprehensive description of the overall background and the significance of the research has been incorporated.]

Comments 2:[L24-26: Consider also mentioning absolute values, rather than only relative values as %]

Response 2:[ The following content has been added: The total biomass ranged from 0.100 to 0.925 Mg ha⁻¹, while the carbon stocks ranged from 0.038 to 0.377 Mg C ha⁻¹]

Comments 3:[L42 - 45: When mentioning the carbon sequestration potential, do you mean both below- and aboveground? Can you be more specific here? Even though the focus of the manuscript lies on aboveground biomass and carbon storage, it might be good to address belowground storage as well (in the Introduction and/or Discussion). A general idea (based on literature) can help to further interpret the aboveground storage potential.]

Response 3:[ When referring to the carbon sequestration potential in the context of the mangrove ecosystem, it encompasses both below - and aboveground components. The biomass aboveground, such as the trunks, branches, and leaves of mangrove trees, contributes significantly to carbon sequestration through photosynthesis, storing carbon dioxide in the form of organic matter. Simultaneously, the belowground biomass, including the extensive root systems of mangroves, also plays a crucial role. Mangrove roots can not only store carbon in the soil but also enhance soil stability, which in turn helps in long - term carbon sequestration. Therefore, when considering the carbon sequestration potential of the mangrove ecosystem, both above and belowground aspects are integral and cannot be overlooked.]

Comments 4:[ L77-84: In my opinion, several remote sensing techniques are also useful as biomass estimation method. This is currently lacking here.]

Response 4:[ I agree you and have improved the related content]

Comments 5:[ L121: How was plot size determined? Based on literature?]

Response 5:[ Based on literature and fieldwork. The fact that mangroves in the investigated plots are identified as shrubs and small trees is a crucial factor. Generally, shrubs and small trees have a relatively smaller canopy spread and root system compared to large trees.  A plot size of 5×10m is likely adequate to include a representative sample of these mangrove individuals, along with their associated understory and soil conditions. This size can capture the primary ecological interactions and characteristics of the mangrove community at the shrub and small - tree stage.]

Comments 6:[ L126: How were roots collected? Please specify this here as well.]

Response 6:[ Root biomass was obtained via full excavation. Roots were carefully extracted from adjacent soil by surface - to - depth digging, then weighed.]

Comments 7:[ L131: Which method was used to determine the carbon content of each component?]

Response 7:[ The dried sample is crushed and screened, and in the automatic solid total organic carbon analyzer, the instrument automatically displays its carbon content.]

Comments 8:[ - L274 - 280: Consider moving this section to the Discussion, or integrate with L312 - 316.]

Response 8:[ I agree. Related sections have been consolidated]

Comments 9:[ Discussion: As mentioned before, it might be relevant to extend the current discussion and also take into account soil carbon storage and remote sensing techniques to provide more/other perspective(s)]

Response 9:[ Relevant content has been improved.]

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript is devoted to the characterisation of the biomass distribution of Kandelia obovata at the northern edge of its range in China and the development of models for estimating the total biomass of trees and its various components. This study is regional in nature, but from a methodological point of view is important as an example of calculating biomass of tree species under specific conditions. The article is well written and the conclusions are based on a fairly large amount of data. However, several questions arose that require clarification.

1. What is the reason for the relatively low carbon content in the roots of Kandelia obovata? How does your data compare to literature sources? Is it possible there is a methodological error such as insufficient purification of samples for analysis? The methodology does not indicate which method or equipment was used to analyze carboncontent in plant material.
2. Low values of the coefficient of determination R² for leaves indicate that the model explains the dependencies rather poorly. Please clarify this point. Perhaps we should have tried other independent variables and their combinations (e.g. number of trees per unit area).
3. Until what age will this type of communities be in the phase of active growth and accumulation of organic matter? At what age will carbon dioxide emissions begin to exceed sequestration. And what is the fate of these plantations in the future.
4. In the Conclusion section it is desirable to add a few sentences about the perspectives for further research in this direction and the practical significance of this study.
5. The tables are numbered out of order. Table 3 is before Table 2.

Author Response

Comments 1: [1.What is the reason for the relatively low carbon content in the roots of Kandelia obovata? How does your data compare to literature sources? Is it possible there is a methodological error such as insufficient purification of samples for analysis? The methodology does not indicate which method or equipment was used to analyze carboncontent in plant material.]

Response 1:[ The relatively low carbon content in the roots of Kandelia obovata can be attributed to multiple factors. First, the root system of Kandelia obovata is highly specialized for water and nutrient uptake in the intertidal zone.  A substantial portion of the carbon fixed by the plant is allocated to above - ground organs to support growth, photosynthesis, and reproduction.  Since the roots primarily function to anchor the plant and absorb resources, this may lead to relatively lower carbon accumulation in the roots. When comparing our data with those from literature sources, we found that some studies also reported relatively lower carbon content in the roots of mangrove species. However, variations exist due to differences in sampling locations, environmental conditions, and plant ages. Regarding the concern about methodological errors, we adhered strictly to standard sample purification procedures. The potassium dichromate oxidation method was employed to determine the carbon content of each component, ensuring the accuracy and reliability of the analysis results.]

Comments 2: [2.Low values of the coefficient of determination R² for leaves indicate that the model explains the dependencies rather poorly. Please clarify this point. Perhaps we should have tried other independent variables and their combinations (e.g. number of trees per unit area).]

Response 2:[ The low coefficient of determination R² for leaves indeed indicates that the current model has limitations in explaining the dependencies. The main reason could be that the independent variables we initially selected did not fully capture all the factors influencing leaf biomass. Leaf growth is regulated by internal genetic factors and influenced by external elements such as soil quality, nutrient availability, and pest pressure. Additionally, the model might not account for potential interactions among these variables, leading to an incomplete understanding of the relationships. In this study, easily - measurable factors, such as diameter at breast height (D), tree height (H), and their combined variables, are utilized to construct biomass estimation models.]

Comments 3: [3.Until what age will this type of communities be in the phase of active growth and accumulation of organic matter? At what age will carbon dioxide emissions begin to exceed sequestration. And what is the fate of these plantations in the future.]

Response 3:[ Kandelia obovata mangroves communities are usually in the stage of active growth and organic matter accumulation during the young stage (generally 10 - 20 years). When the mangroves enter the mature stage (usually 30 - 50 years later), their carbon dioxide emissions may gradually approach or exceed the sequestration.The timescales at which mangroves reach biomass maturity depend on the regional and local attributes of their environmental environment. In this study, the total biomass of 20 - year - old mangroves is still in the incremental stage. Continuous monitoring and conservation of mangroves are essential. We need to implement sustainable management strategies to ensure their long - term survival and the ecological functions they perform.]

Comments 4: [4.In the Conclusion section it is desirable to add a few sentences about the perspectives for further research in this direction and the practical significance of this study.]

Response 4:[ In the Conclusion section, we will add the following sentences about the perspectives for further research and the practical significance of this study. The practical significance of this study lies in providing a scientific basis for mangrove conservation and restoration. The biomass prediction models developed can be used to optimize the planning of mangrove restoration projects, estimate the carbon sequestration potential, and evaluate the effectiveness of conservation measures.]

Comments 5: [5.The tables are numbered out of order. Table 3 is before Table 2.]

Response 5:[ The order has been adjusted in the handscript]

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors, Thank you for your comments. Some minor adjustments are still necessary. The R² values should be added to the figures that do not include the regression coefficient. This applies to images featuring root, stem, and leaf modelling, such as Figure 8. Additionally, in the tables, the mean should be accompanied by a standard deviation.

Author Response

Comments 1: [Dear Authors, Thank you for your comments. Some minor adjustments are still necessary. The R² values should be added to the figures that do not include the regression coefficient. This applies to images featuring root, stem, and leaf modelling, such as Figure 8. Additionally, in the tables, the mean should be accompanied by a standard deviation.]

Response 1:[ Relevant content has been adjusted.]