Conserving Carbon Stocks Under Climate Change: Importance of Trees Outside Forests in Agricultural Landscapes of Mongala Province, Democratic Republic of Congo

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. Please add scientific hypotheses or questions to this paper.
2. How does the research design of this paper reflect climate change?
3. What are the representative aspects of the study area?
4. In the research method, how to ensure the validity of the collected data?
5. Where do large-diameter trees(DBH ≥ 10 cm) come from?
6. What is the research objective of this paper?
7. I think the conclusions should be short and concise.

Author Response

Reviewer 1:

In response to comments 1 and 6 from reviewer 1, we have clarified our research hypothesis and objectives, enhancing the end of the introduction with these revisions highlighted in green. We opted to emphasise the hypotheses rather than framing them as research questions.

To address the second inquiry: “How does the research design of this paper reflect climate change?” we would like to emphasise that our research design is deeply rooted in climate change considerations. It focuses on quantifying and analysing aboveground biomass (AGB) of trees outside forests on agricultural lands (TOF-AL) and compares it to the AGB of undisturbed forests. Here are some key elements:

• Carbon Storage Assessment: By quantifying AGB in TOF-AL and comparing it to forest AGB, we assessed the potential of these non-forest trees to contribute to carbon sequestration.
• Land Use and Climate Change: This study aims to show the importance of TOF-AL in agricultural landscapes in mitigating climate change. Changes in land use, such as deforestation and agricultural expansion, are major drivers of climate change. By examining the carbon storage potential of trees within these changing landscapes, we provide insights into how land management practices can impact climate change mitigation.

• Impacts of Anthropogenic Activities: by including qualitative data on charcoal production and artisanal logging, we reflect an understanding of the anthropogenic pressures that can influence carbon storage and forest degradation. These activities contribute to greenhouse gas emissions and reduce the capacity of forests and TOF-AL to sequester carbon.
• Comparative Analysis: by comparing AGB in TOF-AL to that of undisturbed forests, our study provides a baseline for understanding the relative contribution of these different land cover types to carbon storage. This comparison is essential for assessing the potential of TOF-AL as a climate change mitigation strategy.

In Question 2, Reviewer 1 inquires about the representativeness of Mongala Province concerning our research findings and their applicability to a wider population or similar regions. We assert that Mongala Province exemplifies critical environmental and socioeconomic traits prevalent in various tropical areas across Africa: 

• The province is predominantly covered by vast, dense tropical rainforests, which are increasingly at risk due to deforestation driven by slash-and-burn agriculture, logging, and other human activities.
• Its largely rural population faces significant poverty and relies heavily on forest resources for survival. Therefore, the loss of forests in this area poses not just an environmental and biodiversity crisis but also a direct threat to the survival of the local communities.

In response to question 4, reviewer 1 raises a valid concern regarding the validity of the data collected in this study. We believe this concern is inherently addressed within reviewer 2's comments about potential sampling site selection bias and the uniformity of the data collection protocol. Consequently, the clarifications provided in response to reviewer 2's inquiries and the adjustments made also effectively address reviewer 1's concern. Regarding question 5, the inquiry about "Where do large-diameter trees (DBH ≥ 10 cm) come from?" appears to stem from a typographical error. In our study, "large-diameter trees" specifically refers to those with a DBH of 60 cm or greater. This has been revised in the abstract and highlighted in green for clarity. Lastly, in his seventh comment, reviewer 1 expresses a desire to shorten the conclusion. However, we believe that doing so would compromise the clarity of our study's findings and their broader implications, which we are committed to conveying comprehensively.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The introduction of the article appears to be comprehensive and well-structured. It sets the stage for the study by highlighting the significance of forests in global carbon stock and biodiversity, and elaborates on the critical issue of deforestation driven by human activities such as agriculture, wood energy usage, and logging. Additionally, the introduction underscores the adverse effects of deforestation on the environment, biodiversity, and local communities.

The mentioned options for mitigating deforestation effects, including forest plantations, agroforestry, and traditional tree conservation practices on agricultural lands, provide a logical transition towards the focus of the research. The particular emphasis on the role of trees outside forests on agricultural land (TOF-AL) in preserving carbon stocks is timely and relevant, particularly in the context of the Mongala province in the Democratic Republic of Congo.

However, terminology should be consistent (e.g., "forest carbon stocks" vs "terrestrial carbon stocks").

The research design is thorough and well-structured, addressing multiple aspects necessary for a comprehensive analysis of trees outside forests on agricultural land (TOF-AL) in relation to carbon stock conservation.

However, possible bias should be addressed (e.g., selection bias in choosing villages/fields). Also, additional details on how the integrity of data collection was maintained across varying conditions in the province (e.g., in more inaccessible areas) would add robustness to the research design.

The results are clearly presented, with detailed numerical data, logical organization, and appropriate statistical analysis.

The discussion section effectively synthesizes the study's findings with existing literature and highlights important insights and implications. It provides practical implications and directions for future research, making it suitable and valuable for both academic and practical applications.

The conclusions are robust and adequately supported by the results of the study. Overall, the conclusions are well-crafted, aligning closely with the study’s findings and offering valuable insights for conservation strategies in the region.

Author Response

Reviewer 2:

Reviewer 2 emphasised the importance of consistent terminology, specifically regarding the use of "forest carbon stocks" versus "terrestrial carbon stocks." In response, we have unified the terminology by replacing "terrestrial carbon stocks" with "forest carbon stocks" throughout the entire document. Additionally, the reviewer requested clarification on our approach to minimising bias in village selection and ensuring consistency in the data collection protocol across the province. We have addressed these concerns in the data collection section, with significant changes clearly highlighted in green for easy reference.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors conducted interesting research, but some issues need to be corrected before the article is published. Reading the abstract and the entire manuscript, it seems that it is not explained exactly what AGB is?, DBH (it concerns abbreviations), and even more so TOF-AL? – what is it?, please expand these abbreviations in brackets already at the abstract level. In the methodology, describe and define them in detail.

The introduction is well prepared, the general goal is formulated but there are no details, there are also no research questions or research hypotheses? (should be supplemented).

The methodology has been described well, is there a lack of details about the linear model? Not all data analysis methods used have been listed and described in the research methodology.

Is there no information about the tree species on the sample plots?
The results are well presented but in Figure 5, where R2=0.318? This is a very low value. Was the strength of the relationship calculated correctly? Is the distance from the city really important?

Another observation comes to mind. Since people use wood anyway (90% as reported), does it make sense "to fight" for the protection of AGB on agricultural land? Since this wood will be obtained, for example, from other forest areas of neighboring provinces? Is it worth establishing plantations where it is possible? Please modify the sentence in line 247, where does the statement that it reduces greenhouse gas emissions come from? Please refer to studies on the effect of the age of trees, on the level of carbon sequestration. Many authors state that young trees (i.e. with a lower DBH) absorb more CO2 than old trees.

 

Comments on the Quality of English Language

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Author Response

Reviewer 3:

Reviewer 3 highlighted the importance of defining key abbreviations such as AGB, DBH, and TOF-AL in the abstract. We have taken this feedback seriously and implemented the necessary changes, which are now underlined in green for clarity. Additionally, these terms are thoroughly explained in the methodology section. Reviewer 3 also requested an expanded explanation of the linear regression process, and we believe we have addressed this adequately, with changes marked in green in the methodology section.

Moreover, the reviewer posed a compelling question regarding the coefficient of determination (R²). In response, we've meticulously reviewed our analysis code and discovered that an error had occurred: we inadvertently used AGB instead of AGBcr in the initial analysis. This oversight has been corrected, and we have created a revised figure that reflects the accurate coefficients (refer to Figure 5). For a deeper understanding, we've included screenshots detailing the regression and its validity assumptions. Should you require the full script to explore our methodology further, we will gladly provide it upon request.

References numbers 62 and 63 have been added to this section, and they are also included in the list of references, underlined in green.

Reviewer 3 suggested we revise our comment on line 247, but we believe it is crucial to uphold our original stance. The reviewer’s argument pertains to carbon sequestration, which is distinctly different from the issue of greenhouse gas emissions. When trees are cleared and burned for slash-and-burn agriculture, it leads to increased greenhouse gas emissions. Conversely, by preserving certain trees on agricultural land, we actively mitigate these emissions. Thus, we respectfully disagree with Reviewer 3 and stand by our initial comment.

As for the relevance of advocating for AHF conservation on agricultural lands, it’s vital to emphasize that these trees play a critical role beyond carbon sequestration and climate change mitigation. For local communities in this province, these trees often belong to species of significant use value. By conserving them on agricultural lands, we also protect the sustainability of the valuable goods and services they provide. Furthermore, our findings hold applicability for forests in surrounding provinces that face similar types of pressures. In response to the inquiry about the various species present on these lands, we would like to highlight that we are currently revising another article focused on the diversity and use value of these species preserved on farmland in the Mongala province.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have revised the paper, the quality has been improved, and it is recommended to accept.

Reviewer 2 Report

Comments and Suggestions for Authors

Regarding the comment about maintaining consistent terminology, the revised introduction correctly addresses this:

• At the beginning, it uses "terrestrial carbon stock" consistently: "forests account for a significant portion of the land and store approximately 45% of the terrestrial carbon stock."
• Later on, it switches appropriately to "forest carbon stocks" when discussing deforestation and its effects: "The loss of tropical forests has numerous negative effects on the environment, biodiversity, and the survival of local populations. It results in the loss of biodiversity, the decline of forest carbon stocks, and the reduction of livelihoods for local populations."

Overall, the revised text consistently distinguishes between the broader "terrestrial carbon stock" (all carbon stored across various terrestrial ecosystems) and the more specific "forest carbon stocks" (carbon stored specifically within forests). Therefore, it meets the requirement to use terminology consistently.

 

The revised text in the Materials and Methods section appears to address the comment on possible biases and the integrity of data collection. The revised text now states, "A stratified random sampling approach was employed to ensure the representative sampling of trees outside forests on agricultural lands (TOF-AL) across the province," and "Five villages were selected within each collectivity using a spatially balanced random sampling design, ensuring even geographical distribution and minimising clustering bias." This indicates that stratification and randomization were used to mitigate selection bias during village selection.

The revised text also mentions, "Fields were assigned sequential numbers from the village towards the forest edge to mitigate selection bias... ensuring objectivity and preventing subjective field selection." This helps to prevent any bias in selecting fields for the inventory.

Regarding how inaccessibility might affect data collection integrity, the text now includes, "The application of consistent methodologies across all sampling points ensured the robustness and reliability of the data collected," which implies efforts were made to standardize the methodology across varying conditions to maintain data integrity.

Finally, the methods describe the tools and protocols used consistently, such as, "The area of each field was accurately determined using a Garmin 62s GPS device," and "Qualitative data on charcoal production and artisanal logging presence were collected through semi-structured interviews with field owners in each village, ensuring consistent data collection protocols were followed."

Overall, the revised text has made significant improvements to address the comments on possible bias and ensuring the robustness of data collection.

Reviewer 3 Report

Comments and Suggestions for Authors article corrected. Comments on the Quality of English Language

 The English could be improved to more clearly express the research.