Land Cover and Land Use Changes between 1986 and 2018, and Preliminary Carbon Footprint Implications for Manoka Island (Littoral Region of Cameroon)
, Denis Jean Sonwa 2, Abdon Awono 2, Moustapha Njayou Mama 3, Evariste Fongnzossie 4, Riddley Ngala Mbiybe 1, Lydie Flora Essamba à Rim 2 and Rufin Dominique Ntja 5Round 1
Reviewer 1 Report
This manuscript tries to evaluate the causes and consequences of land-use change in Manoka Island between 1986 and 2018. Accordingly, to estimate C losses in order to strengthen decisions for climate change mitigation. Despite the importance of the theme, the manuscript must be considerably improved before publication.
The introduction is too focused on climate change while this is not the focus of the study (i.e., land-use change). I counted at least 8-fold the term "climate change" while land-use change was mentioned for the first time in the L.55. In general, the introduction must be improved regarding clarity and readability.
Remove "land use" from Keywords. I recommend avoiding Keywords that are present in the title of the manuscript.
L. 41 "temperature rise to 1.5 °C"
L. 108. Please, rephrase the sentence. "Urbanization is eating away these forests…" it sounds weird.
L. 133. Revise the term “Number of channels” in Table 1.
L. 179. Please consider this change: “In December 2019, a sampling campaign was carried out in Manoka Island.”
L. 206. to 212 is repeated. Please remove these sentences.
L. 198. I strongly disagree about "The aerial parts have a higher carbon sequestration rate than the soil reservoirs." There are several studies reporting the opposite. In mangrove forests, soil carbon stocks are around 5-fold higher than aboveground carbon. At least provide a citation for your affirmation.
Figs. 2 and 3. Please, consider improving the quality of the figures. It is quite difficult to identify the legend, the studied sites, etc.
L. 228-229. This is a discussion. Please rephrase it.
Figure 4. What does mean the y axis in the figure?
L. 266-269. This is a discussion.
In section 2.1. Which plant species? Is there any information about height, basal area, age, etc? These details are important for the carbon stocks aboveground estimations.
Please revise commas in tables. Use a comma to separate groups of thousands and dots as decimal separators.
The results should be entirely revised regarding clarity and readability and data presentation.
L. 293-297. Is there any citation for those sentences? Is it based on field observations? How can the authors confirm these results?
L. 306-312. Can these volumes of wood used by fishermen be converted into areas of forests? How representative are these annual harvest rates? Are they replanted? How significant are these Illegal timber harvesting in Epassi regarding C losses?
Section 4.1.2. Right. But, again, is it based on field observations? How can the authors confirm these results? Citations are required here.
Section 4.1.3. Is this forestry law is local or national legislation? Please provide a reference. What does mean MINFOF? What is the relation between Non-compliance with forestry legislation and degradation or deforestation rates?
Section 4.1.4. Once again, what is the relationship between population growth and the results of land cover, land uses, carbon stocks, etc?
Section 4.1.5. A title for the section is missing here.
Sections 4.1.2 to 4.1.6 could be merged into a unique section to discuss the reasons for land-use change associated with anthropic activities. In addition, these discussions should be better associated with the results.
Sections 4.2 to 4.3, in general, must be improved. Afore the main reasons for degradation and deforestation were anthropic activities. These findings could lead to significant C losses and decreased C stocks aboveground. However, in these sections, the authors also associated the C losses with erosion without data to support it. Only based on field observations.
L.380-388: this contextualization is not necessary. This could be mentioned in the introduction. Here you should make this association with the results of the study.
Author Response
Reviewer: 1
Recommendation: Major Revision
Extensive editing of English language and style required
Response: The paper has been edited by a native-speaking academic English editor, and we hope that the language level is now suitable for publication.
Comments:
This manuscript tries to evaluate the causes and consequences of land-use change in Manoka Island between 1986 and 2018. Accordingly, to estimate C losses in order to strengthen decisions for climate change mitigation. Despite the importance of the theme, the manuscript must be considerably improved before publication.
Response: The document has been edited to improve its quality. We took into consideration all the suggestions made by Reviewer 1 and the other two reviewers. However, if after making updates to the paper based on the reviewers’ comments, it appears that some minor issues still need attention, we are open to making further changes.
The introduction is too focused on climate change while this is not the focus of the study (i.e., land-use change). I counted at least 8-fold the term "climate change" while land-use change was mentioned for the first time in the L.55. In general, the introduction must be improved regarding clarity and readability.
Response: The introduction has been improved and provides more detail on land use and land cover, and their relationship with climate change and with mangrove dynamics.
Remove "land use" from Keywords. I recommend avoiding Keywords that are present in the title of the manuscript.
Response: Done.
41 "temperature rise to 1.5 °C"
Response: Correction adopted.
- 108. Please, rephrase the sentence. "Urbanization is eating awaythese forests…" it sounds weird.
Response: This has been changed to: “Urbanization is one of the most important factors influencing…”.
- 133. Revise the term “Number of channels” in Table 1.
Response: This has been changed to: “Number of bands”.
- 179. Please consider this change: “In December 2019, a sampling campaign was carried out in Manoka Island.”
Response: Correction applied.
- 206. to 212 is repeated. Please remove these sentences.
Response: We deleted these sentences.
- 198. I strongly disagree about "The aerial parts have a higher carbon sequestration rate than the soil reservoirs." There are several studies reporting the opposite. In mangrove forests, soil carbon stocks are around 5-fold higher than aboveground carbon. At least provide a citation for your affirmation.
Response: We first corrected this phrase with: ”…the soil reservoirs have a higher carbon sequestration rate than the aerial parts, with 65% per ha within the soil reservoirs (soil and roots) and 35.0% in the aerial biomass, respectively [19]”. At the end we remove this sentence, since in this study we did not collected soil data
Figs. 2 and 3. Please, consider improving the quality of the figures. It is quite difficult to identify the legend, the studied sites, etc.
Response: We improved the quality of Figures 5 and 6 (formerly Figures 2 and 3).
- 228-229. This is a discussion. Please rephrase it.
Response: Phrase corrected.
Figure 4. What does mean the y axis in the figure?
Response: Axes in Figure 7 (formerly Figure 4) have been labeled.
- 266-269. This is a discussion.
Response: Phrase corrected.
In section 2.1. Which plant species? Is there any information about height, basal area, age, etc? These details are important for the carbon stocks aboveground estimations.
Response: Rhizophora racemosa, Rhizophora harrisonii and Avicennia germinans
We also added this phrase in the text:
The average stand density of mangrove forests in Cameroon is 3,255.6 trees/ha in virgin stands, with 80% of trees being in the diameter size class of less than 10 cm, and the stand volume of 427.5 m3/ha corresponds to an above-ground biomass of 305.7 Mg/ha [19].
Please revise commas in tables. Use a comma to separate groups of thousands and dots as decimal separators.
Response: All commas in tables and in the text have been revised.
The results should be entirely revised regarding clarity and readability and data presentation.
Response: The results have been revised.
- 293-297. Is there any citation for those sentences? Is it based on field observations? How can the authors confirm these results?
Response: they are based on field observations. In the text, to confirm these results, we added citations: [54,56].
- 306-312. Can these volumes of wood used by fishermen be converted into areas of forests? How representative are these annual harvest rates? Are they replanted? How significant are these Illegal timber harvesting in Epassi regarding C losses?
Response: Fish smokers undertake a selective harvest (young Rhizophora plants) and do not replant. Gradually, these harvests reduce the possibility of renewal of degraded spaces. We did not convert the biomass to surface as for the moment we did not yet have this proxy/factor
Section 4.1.2. Right. But, again, is it based on field observations? How can the authors confirm these results? Citations are required here.
Response: This is based on field observations. In the text, as support for these results, we added several citations: [56,60,61,62].
Section 4.1.3. Is this forestry law is local or national legislation? Please provide a reference. What does mean MINFOF? What is the relation between Non-compliance with forestry legislation and degradation or deforestation rates?
Response: The contents of the section have been revised to better respond to these questions.
Section 4.1.4. Once again, what is the relationship between population growth and the results of land cover, land uses, carbon stocks, etc?
Response: The contents of the section have been revised to provide expectations that are linked population growth and some other factors.
Section 4.1.5. A title for the section is missing here.
Response: Title added as well as suitable text.
Sections 4.1.2 to 4.1.6 could be merged into a unique section to discuss the reasons for land-use change associated with anthropic activities. In addition, these discussions should be better associated with the results.
Response: We understand and appreciate the reviewer’s suggestion. However, we prefer to provide information in a format that allows a better understanding of the context of this study. In Section 4, we began by discussing first the direct drivers (Fuel wood harvest and Urban & infrastructure development) and then the indirect drivers. With this in mind, we prefer to retain separate sections and subsections to aid those readers who are used to the REDD+ framework (or Lambin Framework), where the two sections are kept separate.
Sections 4.2 to 4.3, in general, must be improved. Afore the main reasons for degradation and deforestation were anthropic activities. These findings could lead to significant C losses and decreased C stocks aboveground. However, in these sections, the authors also associated the C losses with erosion without data to support it. Only based on field observations.
Response: These sections have been improved in accordance with the reviewer comments.
L.380-388: this contextualization is not necessary. This could be mentioned in the introduction. Here you should make this association with the results of the study.
Response: We revised the document in general and made an effort to put the findings in the context of climate change responses.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article submitted to me for evaluation concerns interesting issues focusing on changes in land use in a fragment of the coastal zone of Cameroon. The work is interesting, but not devoid of minuses that should be corrected before possible publication. First of all, the question arises, what new does this study bring to the subject matter? Are the observed patterns of land use changes also noticeable in other parts of the coastal zone of other African countries or other parts of the world with mangrove forests? The research procedure is insufficiently described.
The drawback of the work is the poor literature review on the functioning of mangrove forests, land use changes in the areas where they occur, the impact of contemporary climate changes on this type of ecosystems and the issues of land use changes in terms of methodology (Solarski, Krzysztofik, 2021). Below are some examples of publications that would enrich the cited literature and broaden the context. Of course, there are many more publications of this type, so I believe that the number of 32 publications quoted is insufficient.
Several items that are worth considering in the literature review are listed below:
Obiefuna, Jerry N., Okolie, Chukwuma J., Atagbaza, Ajiri O., Nwilo, Peter C. and Akindeju, Folayele. O .. "Spatio-temporal land cover dynamics and emerging landscape patterns in western part of Lagos State, Nigeria" Environmental & Socio-economic Studies, vol.9, no.3, 2021, pp. 53-69. https://doi.org/10.2478/environ-2021-0017
Biggs, R., Simons, H., Bakkenes, M., Scholes, R. J., Eickhout, B., van Vuuren, D., & Alkemade, R. (2008). Scenarios of biodiversity loss in southern Africa in the 21st century. Global Environmental Change, 18(2), 296– 309. https://doi.org/10.1016/j.gloenvcha.2008.02.001
Hill, S. L. L., Gonzalez, R., Sanchez-Ortiz, K., Caton, E., Espinoza, F., Newbold, T., et al. (2018). Worldwide impacts of past and projected future land-use change on local species richness and the Biodiversity Intactness Index. BioRxiv, 311787. https://doi.org/10.1101/311787
Solarski, M.; Krzysztofik, R. Is the Naturalization of the Townscape a Condition of De-Industrialization? An Example of Bytom in Southern Poland. Land 2021, 10, 838. https://doi.org/10.3390/land10080838
Stéphenne, E.F. Lambin, A dynamic simulation model of land-use changes in Sudano-sahelian countries of Africa (SALU), Agriculture, Ecosystems & Environment, Volume 85, Issues 1–3, 2001, Pages 145-161,
Dagnachew Legesse, Christine Vallet-Coulomb, Françoise Gasse, Hydrological response of a catchment to climate and land use changes in Tropical Africa: case study South Central Ethiopia,
Journal of Hydrology, Volume 275, Issues 1–2, 2003, Pages 67-85,
A.C. Guzha, M.C. Rufino, S. Okoth, S. Jacobs, R.L.B. Nóbrega,
Impacts of land use and land cover change on surface runoff, discharge and low flows: Evidence from East Africa, Journal of Hydrology: Regional Studies,
Volume 15, 2018, Pages 49-67, ISSN 2214-5818, https://doi.org/10.1016/j.ejrh.2017.11.005.
Otieno VO, Anyah RO (2012) Effects of land use changes on climate in the Greater Horn of Africa. Clim Res 52:77-95. https://doi.org/10.3354/cr01050
Gyamfi, C.; Ndambuki, J.M.; Salim, R.W. Hydrological Responses to Land Use/Cover Changes in the Olifants Basin, South Africa. Water 2016, 8, 588. https://doi.org/10.3390/w8120588
Alongi, D.M. Impact of Global Change on Nutrient Dynamics in Mangrove Forests. Forests 2018, 9, 596. https://doi.org/10.3390/f9100596
Etemadi, H., Smoak, J.M. & Karami, J. Land use change assessment in coastal mangrove forests of Iran utilizing satellite imagery and CA–Markov algorithms to monitor and predict future change. Environ Earth Sci 77, 208 (2018). https://doi.org/10.1007/s12665-018-7392-8
Murdiyarso, D., Purbopuspito, J., Kauffman, J. et al. The potential of Indonesian mangrove forests for global climate change mitigation. Nature Clim Change 5, 1089–1092 (2015). https://doi.org/10.1038/nclimate2734
Figure 4 needs improvement, what are the units on the x axis? The signatures of individual categories of land use on the chart should be changed, they can, for example, be marked with abbreviations, the meaning of which will be described in the legend.
Moreover, in many places the authors incorrectly cite the literature, e.g. soils to the air also oxidizes soil carbon and releases it as CO2 (Hiraishi et al. 2014) [30]. (verse 387)
Author Response
Comments and Suggestions for Authors
The article submitted to me for evaluation concerns interesting issues focusing on changes in land use in a fragment of the coastal zone of Cameroon. The work is interesting, but not devoid of minuses that should be corrected before possible publication. First of all, the question arises, what new does this study bring to the subject matter? Are the observed patterns of land use changes also noticeable in other parts of the coastal zone of other African countries or other parts of the world with mangrove forests? The research procedure is insufficiently described.
Response: The paper has been revised, starting with the introduction where new literature has been included that locates our study in the context of other studies on coastal zones and mangrove management. Few studies of this nature exist for Cameroon and Africa. So having such a study is important for the local coastal landscape of Manoka and for similar ecosystems in Cameroon and abroad. In the specific context of Cameroon, the more emission factors and activities data we have, the better. We thank Reviewer 2 for the suggestions, which were taken into consideration along with those of the other two reviewers. If we have overlooked some issues that arise from these comments that still need to be considered before publication, we are open to making further minor changes.
The drawback of the work is the poor literature review on the functioning of mangrove forests, land use changes in the areas where they occur, the impact of contemporary climate changes on this type of ecosystems and the issues of land use changes in terms of methodology (Solarski, Krzysztofik, 2021). Below are some examples of publications that would enrich the cited literature and broaden the context. Of course, there are many more publications of this type, so I believe that the number of 32 publications quoted is insufficient.
Response: Many thanks for this very useful literature list. The contents of the document have been improved regarding these observations. Literature citations have been enriched in the revised version.
Figure 4 needs improvement, what are the units on the x axis? The signatures of individual categories of land use on the chart should be changed, they can, for example, be marked with abbreviations, the meaning of which will be described in the legend.
Response: Figure 7 (formerly Fig. 4) has been improved, and units along both axes were introduce.
Moreover, in many places the authors incorrectly cite the literature, e.g. soils to the air also oxidizes soil carbon and releases it as CO2 (Hiraishi et al. 2014) [30]. (verse 387)
Response: This has been corrected in the revised version.
Reviewer 3 Report
The manuscript compared the land use changes of Manoka Island between 1986 and 2018, and computed the carbon loss due to the degradation of forests. The manuscript is understandable, but I suggest major revision before it can be published. The methodology on land use classification and carbon computation is commonly applied in many previous studies, so the author must highlight the specialty of their work in term of the results and discussions. It also required proof reading prior of publication. Please refer to attached document for more comments.
Comments for author File: Comments.pdf
Author Response
Comments and Suggestions for Authors
The manuscript compared the land use changes of Manoka Island between 1986 and 2018, and computed the carbon loss due to the degradation of forests. The manuscript is understandable, but I suggest major revision before it can be published. The methodology on land use classification and carbon computation is commonly applied in many previous studies, so the author must highlight the specialty of their work in term of the results and discussions. It also required proof reading prior of publication.
Response: We thank Reviewer 3 for these comments and suggestions: we have revised the study based on the suggestions of all three reviewers. We also asked a science editor to edit the paper. Thus, we hope that the paper is now acceptable for publication. However, if we have overlooked some issues that arise from these comments that still need to be considered before publication, we are open to making further minor changes.
Some of my main comments to improve the manuscript are:
The classification is based on the maximum likelihood algorithm, what are the reason to use maximum likelihood classifier? Are there any pre-processing of the Landsat images before the classification? Authors must clarify these procedures.
Response: The classification method has been corrected in the revised version, which provides more detail on the pre-processing of the Landsat images before their classification and the reason for using the maximum likelihood algorithm.
In terms of field data collection for land use classification, how many reference points were collected in total? How many were used as training and how many were used for validation?
Response: More information about reference points collected and their use in the process of classification and validation are presented in detail in the revised version. In addition, we added 2 figures in the revised version which show an Overview of the verification/validation tracking segments of the classification
Most of the discussion are focusing only on mangrove, the authors did not discuss the how the inland forest loss impact the island.
Response: Discussion has been improved in the new version of the manuscript and those aspects have been integrated.
The clear link between the journal theme: Sustainability and the land use changes, and carbon loss is not discussed. The results and discussion need to be improved. For example, most of the forest clearance/ carbon loss are found to due by the local exploration and local usage, and some actions were taken to reduce the logging activity, but how these actions promote sustainability in the island over the period? Are these actions working? How these action shows the Sustainability (changes on environmental, community, economic, cultural etc.) in the study area?
Response: The Results section has been modified and provides more detail in the revised version. The Discussion has been revised using more recent references.
Minor comments:
Check the format of decimal point and be consistent – some are comma (,) some are dot (.), for example Line 23 and Line 49. Line 227: 3814,85 or 3814.85?
Response: The presentation of decimal numbers has been corrected in the text. All commas in tables and in the text have been revised.
Line 106 – 107: the sentence is not clear, please revise.
Response: This sentence has been revised in the new version.
Line 121: delete the space between the word “study” and “;”
Response: Correction applied.
Line 144: why there is a “ prior of the word identify?
Response: Phrase corrected.
It would be great to provide a figure of all the satellite images used in the study – to show the condition of clouds, shadow, and the stripping of the Landsat 7 ETM+ image.
Response: We introduced a new figure that provides these images.
Line 146: themes or classes? In Table 2 you used Occupancy class but, in the text, you used themes, suggest being consistent throughout the manuscript.
Response: In the revised version, we corrected themes to classes.
Line 162: What is the meaning of: evaluated the accuracy of the soil occupation maps? I think what you refer to is the classification maps?
Response: Yes, we corrected it in the revised version to classification maps.
Line 172 – 177: please take note on the flow of the manuscript – why these sentences are written in point form?
Response: The manuscript has been revised to improve the flow.
Line 180: be specific – list which image(s) is the one close to the period of field data collection. I believe only the image acquired in 2018 is valid here.
Response: Yes, we have specified it in the new version. It is the Image acquired in 2018.
Line 198: The aerial parts have a higher carbon sequestration rate than the soil reservoirs. Is this statement true for both inland forest and mangrove? Can you provide reference and descriptions for this statement?
Response: We first corrected this phrase as follows: “the soil reservoirs have a higher carbon sequestration rate than the aerial parts, with 65% per ha within the soil reservoirs (soil and roots) and 35.0% in the aerial biomass, respectively [19]”. At the end we remove this sentence, since in this study we did not collected soil data
Table 4: For Mangrove, you used Greatly exploited; for Inland Forest, you used Intensively exploited. In Line 200, you used heavily exploited. What are the differences between Greatly, Intensively, and heavily? If none, please consider using the same word.
Response: In the revised version, we used only greatly exploited.
Line 206 – 213: Repeated, see Line 192 – 200.
Response: These sentences have been deleted.
The fonts of text in Figure 2 and Figure 3are not readable, they should be increased.
Response: We improved the quality of Figures 5 and 6 (formerly Figs 2 and 3) in the text.
Line 230: How about the area and percentage of Bare surface and Water?
Response: The percentage and the area of bare surface and water are introduced in this version of the text.
Line 223 – 224: fig 3 and fig 4 – check if this is the correct format required by the journal.
Response: These figures have been corrected.
Are Figure 2 and Figure 3 (right side) the same maps? If so, why you need Figure 2?
Response: Figure 5 (formerly Figure 2) has been retained because it was used to illustrate land cover land use in 2018 and the description is useful in assessing carbon storage.
Figure 4: indicate the unit of the y-axis.
Response: Units of measurement along both axes are indicated in the corrected version (figure 7).
Line 264: “17.8 ha of degraded mangrove have been converted into habitat”, what “habitat” here means?
Response: In the revised version, habitat has been corrected to built-up space.
Line 276: Landsat, not landsat.
Response: Correction applied.
Table 5: where is the value for intensively exploited mangrove?
Response: The table had been edited and the data related to the land uses/cover category/Typology included when necessarily (This mean when the land use/cover category exist during the study period). (See Table 6.)
Table 6 is the same with Table 4.
Response: Table 6 has been deleted in the revised version.
Line 286 – 288 is repeated, see Line 203 – 205.
Response: This sentence has been deleted in the revised version.
Revise the caption of Figure 6 by marking the photos.
Response: Photos are marked in revised version.
Check citation format e.g. Line 387 and Lin 388.
Response: The citation format has been corrected.
Round 2
Reviewer 2 Report
After the changes have been made, the article may be considered for publication.
Author Response
we Thanks the reviewer for the comments. We updated the paper base on details suggestion provided by the reviewer 3 who was more specific.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript has been improved. I recommend it for publication after considering the following minor issues.
Line65 – 66: " They are an important carbon sink and therefore play a key role in mitigating climate change." This sentence sounds repetitive from the above statements. Consider remove.
I still think Figure 5 and Figure 6 (right) are carrying the same information, so Figure 5 is not necessary and can be deleted, authors can refer the descriptions they have written based on Figure 5 to Figure 6 (right) since both are the same.
Line 386: remove the minus (-) sign.
Author Response
Comments and Suggestions for Authors
The manuscript has been improved. I recommend it for publication after considering the following minor issues.
Response: We thanks the reviewer 3 for recommending publication of our paper after taking in consideration some minors suggestions. We took those suggestions in consideration, and we hope that the paper can now be finally accepted for publication.
Line65 – 66: " They are an important carbon sink and therefore play a key role in mitigating climate change." This sentence sounds repetitive from the above statements. Consider remove.
Response: We deleted this sentence.
I still think Figure 5 and Figure 6 (right) are carrying the same information, so Figure 5 is not necessary and can be deleted, authors can refer the descriptions they have written based on Figure 5 to Figure 6 (right) since both are the same.
Response: Figure 5 have been deleted. In addition, we added one table in the revised version which show land cover and land uses classes in 2018. We hope that this can allow the reader to have a rapid overview of land covers & uses of this Island.
Line 386: remove the minus (-) sign.
Response: We deleted this sign.
Author Response File: Author Response.pdf
