Carbon Offset Service of Urban Park Trees and Desirable Planting Strategies for Several Metropolitan Cities in South Korea
Round 1
Reviewer 1 Report
Carbon peak and carbon neutralization is one of the hotspots in the world. Urban forest is the important part of vegetation for carbon storage and carbon sequestration. But the ability of carbon storage and carbon sequestration by urban forest are quite different for the species composition and structures of urban forest ecosystems, land-use and human activities. And there are different experiences to be exchanged in different cities, countries and regions. So research frontiers in carbon storage and carbon sequestration in the world can be followed by the topic of the manuscript. However there were several big problems and some detailed problems should be discussed in the manuscript. The main problems is as follow:
1 The topic of of the title is too broad so that none scientific problems can be summarized in the part of introduction and the study is only status description. And carbon offset service of urban park trees can not been represented by two of sampled cities. Thus the study is only a case study. I suggest that the topic of the manuscript should be concentrated on one or several scientific problems, and the title of the manuscript should be summarized on basis of proposed scientific problems.
2 The structure of the manuscript should be revised. The content in the subtitle 3.1 (line 134) should be integrated into "material and methods" according to the topic in the manuscript. And The part of 3.2 (line 155) should be also integrated into the part of "material and methods", or this part can be utilized in discussion when you want to explain the affecting mechanisms of result. And The part of 3.4 (line 277) should be taken as suggestion in conclusion. Because contents in the three parts were no directly relations with carbon storage of urban trees and the content of part 3.2 belongs to urban tree structure. Therefore the remained result was only 3.3. Thus the composition of result was were simple. I suggest that the remained result should be expended or revised according to proposed scientific problems. The part of discussion which is very important part in scientific papers to explain mechanisms of results was absent in the manuscript.
3 line 50-56: The writing style belongs to the literature accumulation, and regular results should be summarized.
4 Line 63-65 and line 66-68: there were grammar problems.
5 Line 66: Urban park belongs to one type of greenspaces, so the phrase of “urban park” is redundant.
6 Line 80 “systematic random sample”: The sampling method was not clearly expressed because systematic sample is quite different with random sample. The eight of sample lines were systematic method, and sampled parks were random method. But I suggest that total numbers of parks were crossed by the eight sampled lines should be states. And the proportion of crossed parks by sampled lines taking total parks in the two cities should be also introduced in the method. I suggest that a table including park types and size classes and number or area proportion of sampled parks taking total parks in each class in target cities to prove the scientificalness and rationality of the methods.
7 Line 115-117: I argued about the method of “carbon uptake and storage of trees in urban parks were calculated by applying the quantitative model per tree species developed for open-grown urban trees”. The carbon storage of urban trees will be overestimated by this method and be not the current status. So mechanical sample method or stratified sampling is the best one on basis of estimation precision, and all of trees in one sampled plot should be investigated. The current method is OK if tree carbon storage in species scale is estimated. Tree sizes were affected by neighbor competition, tree ages, and grown environments such as heat island and other site conditions. The influences is worth to researched to explain affecting mechanisms of variation in tree carbon storage.
8 Line 244-253 figure 3: What is the reasons of carbon uptake and storage variable? This maybe the scientific problems in the manuscript. But the status of carbon uptake and storage were only compared in the manuscript.
Comments for author File: 
Comments.pdf
Author Response
We would like to express our sincere appreciation for your kind and invaluable comments on our paper. Your comments have been thoroughly reviewed and then reflected. Our revisions and answers to each comment are as follows:
Point 1
The topic of the title is too broad so that none scientific problems can be summarized in the part of introduction and the study is only status description. And carbon offset service of urban park trees can not been represented by two of sampled cities. Thus the study is only a case study. I suggest that the topic of the manuscript should be concentrated on one or several scientific problems, and the title of the manuscript should be summarized on basis of proposed scientific problems.
Response 1
Thanks for your detailed comments. We have revised the title of the paper reflecting your opinion (Lines 2-3).
Point 2
The structure of the manuscript should be revised. The content in the subtitle 3.1 (line 134) should be integrated into "material and methods" according to the topic in the manuscript. And The part of 3.2 (line 155) should be also integrated into the part of "material and methods", or this part can be utilized in discussion when you want to explain the affecting mechanisms of result. And The part of 3.4 (line 277) should be taken as suggestion in conclusion. Because contents in the three parts were no directly relations with carbon storage of urban trees and the content of part 3.2 belongs to urban tree structure. Therefore the remained result was only 3.3. Thus the composition of result was simple. I suggest that the remained result should be expended or revised according to proposed scientific problems. The part of discussion which is very important part in scientific papers to explain mechanisms of results was absent in the manuscript.
Response 2
We have revised the structure of the manuscript. We have added a Discussion section (Lines 310-433). The content about study city in subtitle 3.1 has been moved to Materials and Methods (Lines 100-106). However, the content about the type of land cover was retained as it was the result of the survey and analysis (Lines 199-207). Most of the previous studies have described the tree planting structure in the Results section, so we have also kept this content in the same section (Lines 211-243). However, following your recommendation, subtitle 3.3 was created to further analyze the relationship between the planting structure and carbon offset service (Lines 292-309). Moreover, subtitle 4.3 of the Discussion was expanded. Subtitle 3.4 has been moved to the Discussion following the recommendations by the reviewers (Lines 364-402).
Point 3
line 50-56: The writing style belongs to the literature accumulation, and regular results should be summarized.
Response 3
We have revised the literature review in response to your kind comments. We have provided more details regarding the results and the contents of previous studies (Lines 50-69).
Point 4
Line 63-65 and line 66-68: there were grammar problems.
Response 4
Thanks for your detailed comment. We have revised the sentences and applied English corrections in response to your comment (Lines 72-77).
Point 5
Line 66: Urban park belongs to one type of greenspaces, so the phrase of “urban park” is redundant.
Response 5
By deleting the “urban greenspace”, we have emphasized the “urban park”, which is the subject of this study (Lines 75-77).
Point 6
Line 80 “systematic random sample”: The sampling method was not clearly expressed because systematic sample is quite different with random sample. The eight of sample lines were systematic method, and sampled parks were random method. But I suggest that total numbers of parks were crossed by the eight sampled lines should be states. And the proportion of crossed parks by sampled lines taking total parks in the two cities should be also introduced in the method. I suggest that a table including park types and size classes and number or area proportion of sampled parks taking total parks in each class in target cities to prove the scientificalness and rationality of the methods.
Response 6
We have revised the sampling method according to your suggestion (Lines 108-114). We selected parks distributed within a distance of 500 m from the point of intersection between the circle and the line or a point of contact as a sample. A minimum of three and a maximum of six parks were selected from each of the eight lines. The number of sample parks in this study was equal to 4.4% and 6.2% of the total number of urban parks in Daejeon (579 parks) and Daegu (797 parks), respectively. In addition, based on your comments, we have added a table that includes the number and type of sample parks (Lines 134-135).
Point 7
Line 115-117: I argued about the method of “carbon uptake and storage of trees in urban parks were calculated by applying the quantitative model per tree species developed for open-grown urban trees”. The carbon storage of urban trees will be overestimated by this method and be not the current status. So mechanical sample method or stratified sampling is the best one on basis of estimation precision, and all of trees in one sampled plot should be investigated. The current method is OK if tree carbon storage in species scale is estimated. Tree sizes were affected by neighbor competition, tree ages, and grown environments such as heat island and other site conditions. The influences is worth to researched to explain affecting mechanisms of variation in tree carbon storage.
Response 7
As already suggested in the method, we conducted a field survey on the species, size, and planting density of all trees in the park, and applied this to quantitative models for each tree species to quantify the carbon offset service (Lines 138-139, 167-169). In other words, this study quantified the carbon uptake and storage of all trees planted in the park, not just some trees.
Point 8
Line 244-253 figure 3: What is the reasons of carbon uptake and storage variable? This maybe the scientific problems in the manuscript. But the status of carbon uptake and storage were only compared in the manuscript.
Response 8
Variables such as park area, crown cover, and basal area have often been used as carbon indicators for urban greenspaces in previous studies. Considering your comments, we further deepened the discussion on the comparison of carbon indicators between this work and previous studies (Lines 174-175, 313-315).
Author Response File: 
Author Response.docx
Reviewer 2 Report
The work presented in the manuscript is an interesting and an important article. However, there are some places that need improvement.
Introduction - at present, the section reads disjointedly. It needs to have a smooth flow. In fact, one paragraphs has only one sentence, while most paragraphs are 2-3 sentences. You could group the current content, flesh out where needed, and add some new information to form the background to your work.
Results - there is a lot of information presented in both the tables and the figures. However, only a minute percentage of this information has been discussed under the Results section.
Conclusions - I suggest to separate Discussions and conclusions into 2 sections, as given in the journal template. You have not done justice to your findings. All the important findings that you pointed out in the Results section need to be discussed in detail under the Discussion section. Both the Results and the Discussion sections need to be improved.
When reformulating the Conclusions section, remind the reader what your objectives were, and summarize the key findings before concluding the work.
English must be revised.
Author Response
We would like to express our sincere appreciation for your kind and invaluable comments on our paper. Your comments have been thoroughly reviewed and then reflected. Our revisions and answers to each comment are as follows:
Point 1
Introduction - at present, the section reads disjointedly. It needs to have a smooth flow. In fact, one paragraphs has only one sentence, while most paragraphs are 2-3 sentences. You could group the current content, flesh out where needed, and add some new information to form the background to your work.
Response 1
Thanks for your detailed comment. In the Introduction, we have expanded the literature review and emphasized the necessity of this study (Lines 50-83).
Point 2
Results - there is a lot of information presented in both the tables and the figures. However, only a minute percentage of this information has been discussed under the Results section.
Conclusions - I suggest to separate Discussions and conclusions into 2 sections, as given in the journal template. You have not done justice to your findings. All the important findings that you pointed out in the Results section need to be discussed in detail under the Discussion section. Both the Results and the Discussion sections need to be improved. When reformulating the Conclusions section, remind the reader what your objectives were, and summarize the key findings before concluding the work.
Response 2
We have added a Discussion section according to your suggestion (Lines 310-433). This section included the main findings and their implications that were not covered in the Results. Thank you for your kind suggestion.
Point 3
English must be revised.
Response 3
This revised paper has undergone English corrections in response to your comments.
Author Response File: Author Response.docx
Reviewer 3 Report
The paper reports carbon uptake and storage by urban park vegetation in two South Korean cities and discusses measures available for increasing the amount of carbon sequestered and stored in park vegetation. The topic is interesting and valid, and it seems the authors have collected adequate data using methods appropriate for the study.
However, the methods used need are reported too loosely. The authors should explain how they measured tree cover and layering structure and how the importance value of species and layering planting structure were estimated. They should also note how they estimated the cover of shrubs, grass, herbaceous plants, and pavements (there is nothing about this in methods, but the results give cover estimates for these elements; shrubs seem to be also measured for carbon uptake and storage). In addition, the statistical methods used for data analysis should be described.
In Results and Discussion, there is unnecessary repetition in the body text, which often gives similar numerical results as is presented in tables or figures (which are seldom referred to). The results are discussed quite scantly leaving most recent papers on the carbon sequestration efficiency non-utilized (see e.g. https://doi.org/10.1016/j.ufug.2021.127291 and references therein). In my mind, the conclusions on which factors affected carbon uptake and storage most are not justified as the impact of tree species, density, size, or vertical structure was not statistically analyzed (or not reported in any case).
The English language should be thoroughly revised; the construction of the text often makes it hard to comprehend (e.g. page 3, lines 120-123, page 5 lines 164-166 and 170-171, p. 6 lines 201-202, p. 9 lines 315-317). Captions in figures and tables should be improved and/or corrected. It seems to me the authors often use "total" when they mean average, in tables and figures. Signs of statistical significance are missing in all tables and figures. The authors should also tell strictly if and when the results are reported per unit park or vegetation area, as pavements and facilities covered more than half of park area on average (wouldn't this be an apparent point where carbon offset could be enhanced, by increasing the overall vegetation cover at the expense of hard structures?).
Author Response
We would like to express our sincere appreciation for your kind and invaluable comments on our paper. Your comments have been thoroughly reviewed and then reflected. Our revisions and answers to each comment are as follows:
Point 1
However, the methods used need are reported too loosely. The authors should explain how they measured tree cover and layering structure and how the importance value of species and layering planting structure were estimated. They should also note how they estimated the cover of shrubs, grass, herbaceous plants, and pavements (there is nothing about this in methods, but the results give cover estimates for these elements; shrubs seem to be also measured for carbon uptake and storage). In addition, the statistical methods used for data analysis should be described.
Response 1
Thank you for your valuable comment. In the Materials and Methods section, we have added an explanation about how we estimated the crown cover, importance value, vertical structure, and type of land cover of study parks (Lines 143-156). In addition, we have added an explanation of the statistical method used for data analysis (Lines 188-195).
Point 2
In Results and Discussion, there is unnecessary repetition in the body text, which often gives similar numerical results as is presented in tables or figures (which are seldom referred to). The results are discussed quite scantly leaving most recent papers on the carbon sequestration efficiency non-utilized (see e.g. https://doi.org/10.1016/j.ufug.2021.127291 and references therein). In my mind, the conclusions on which factors affected carbon uptake and storage most are not justified as the impact of tree species, density, size, or vertical structure was not statistically analyzed (or not reported in any case).
Response 2
Based on your recommendation, we have calculated the correlation coefficients of the variables (including the tree species, density, size, and type of land cover) and carbon offset services to elucidate the factors affecting carbon uptake and storage (Lines 292-307). We have added the paper you recommended to the Discussion (Lines 398-400). In addition, we have separated the Results and Discussion sections and expanded them (Lines 310-433).
Point 3
The English language should be thoroughly revised; the construction of the text often makes it hard to comprehend (e.g. page 3, lines 120-123, page 5 lines 164-166 and 170-171, p. 6 lines 201-202, p. 9 lines 315-317). Captions in figures and tables should be improved and/or corrected. It seems to me the authors often use "total" when they mean average, in tables and figures. Signs of statistical significance are missing in all tables and figures. The authors should also tell strictly if and when the results are reported per unit park or vegetation area, as pavements and facilities covered more than half of park area on average (wouldn't this be an apparent point where carbon offset could be enhanced, by increasing the overall vegetation cover at the expense of hard structures?).
Response 3
This revised paper has undergone English corrections in response to your comments. To help the reader's understanding, "total" in tables and figures has been changed to "mean" (Table 3-5, Figure 3). We have added the statistical significance to tables and figures (Table 3-6, Figure 3). In addition, we have explained that both the vegetation and pavement/facility area are reflected in the carbon uptake and storage per unit area, and clarified that the carbon offset service can be enhanced if the hard surface is reduced (Lines 355-362).
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
All revisions have bene accepted and done in the manuscript.
I suggest to accept the paper.
Author Response
We appreciate your positive review. Wish you the best for 2023.
Reviewer 3 Report
In my opinion, the authors have made considerable improvements in the paper. Separating Results and Discussion made the report clearer and more readable, and the clarity and language has got notably better. However, I still suggest some revision:
In the Introduction, line 56 please correct the following expression: "are different 4.5 times at maximum".
In chapter 2.2., please tell that you also investigated shrubs in the study parks and how was that done? (in Results you report carbon uptake by trees and shrubs) On the other hand, why do you describe the calculation of importance values, but do not report any importance value results? The sentence on lines 149-150 has some word(s) missing.
In chapter 3.1., the sentence on lines 203-205 is incomprehensible (both cities exceeded the mean value?). In Table 3, I'd recommend using "Other" instead of "Etc." In Figure 2, replace "Total" with "Mean"
In chapter 3.2., correct the first sentence so it comes clear you measured carbon uptake of TREES AND SHRUBS per unit area of the study parks. In my opinion, the text on lines 262-277 belongs to the Discussion, not to the Results section where it now is.
In chapter 4.4., on line 409 something is missing; should it maybe be "the carbon EMISSION per unit area"
Author Response
We would like to express our sincere appreciation for your kind comments on our paper. We also have been marked the parts of the revised manuscript in yellow. Our revisions and answers to each comment are as follows:
Point 1
In the Introduction, line 56 please correct the following expression: "are different 4.5 times at maximum".
Response 1
Thanks for your detailed comment. In the Introduction, we have revised this sentence reflecting your opinion (Lines 55-56).
Point 2
In chapter 2.2., please tell that you also investigated shrubs in the study parks and how was that done? (in Results you report carbon uptake by trees and shrubs) On the other hand, why do you describe the calculation of importance values, but do not report any importance value results? The sentence on lines 149-150 has some word(s) missing.
Response 2
We have added an explanation about how we investigated shrub reflecting your comment (Line 138, Lines 139-141). In addition, we have revised the sentence about the calculation method of importance values (Lines 145-147). The importance value results are already suggested in Results (Lines 227-233).
Point 3
In chapter 3.1., the sentence on lines 203-205 is incomprehensible (both cities exceeded the mean value?). In Table 3, I'd recommend using "Other" instead of "Etc." In Figure 2, replace "Total" with "Mean"
Response 3
Based on your opinion, we have revised the sentence (Lines 203-205), Table 3 (Line 208), and Figure 2 (Line 240). Thanks for your valuable comment.
Point 4
In chapter 3.2., correct the first sentence so it comes clear you measured carbon uptake of trees and shrubs per unit area of the study parks. In my opinion, the text on lines 262-277 belongs to the Discussion, not to the Results section where it now is.
Response 4
We have revised the sentence to clarify the meaning of carbon uptake by trees and shrubs (Line 249). We have moved the text on lines 262-277 to Discussion reflecting your opinion (Lines 310-327).
Point 5
In chapter 4.4., on line 409 something is missing; should it maybe be "the carbon EMISSION per unit area"
Response 5
We have revised this sentence reflecting your valuable comment (Line 406).
Author Response File: Author Response.docx
