Assessing the Carbon Storage of Soil and Litter from National Forest Inventory Data in South Korea

Round 1

Reviewer 1 Report

The authors of the article “Assessing the carbon storage of soil and litter from national forest inventory data in South Korea”present soil carbon results from the national forest inventory in South Korea as well as models and maps in order to assess soil and litter carbon stocks for South Korea. The manuscript is an important contribution for the global and national evaluation of carbon stocks and should be of interest for the readers of “forests”.

The article is written and structured clearly and I want to suggest publication after some points have been revised. There are two general points and some points in detail.

In General:

1. The presentation would benefit by including further international publications, which deal with carbon stocks in forests soils, especially in temperate regions. There is important research from Europe, e.g.:

Grüneberg E., Schöning I., Riek W., Ziche D., Evers J. (2019) Carbon Stocks and Carbon Stock Changes in German Forest Soils. In: Wellbrock N., Bolte A. (eds) Status and Dynamics of Forests in Germany. Ecological Studies (Analysis and Synthesis), vol 237. Springer, Cham. https://0-doi-org.brum.beds.ac.uk/10.1007/978-3-030-15734-0_6

Vanguelova, E.I., Bonifacio, E., De Vos, B. et al. Sources of errors and uncertainties in the assessment of forest soil carbon stocks at different scales—review and recommendations. Environ Monit Assess 188, 630 (2016). https://0-doi-org.brum.beds.ac.uk/10.1007/s10661-016-5608-5

Bruno De Vos, Nathalie Cools, Hannu Ilvesniemi, Lars Vesterdal, Elena Vanguelova, Stefano Carnicelli, Benchmark values for forest soil carbon stocks in Europe: Results from a large scale forest soil survey, Geoderma, Volumes 251–252, 2015, Pages 33-46, ISSN 0016-7061, https://0-doi-org.brum.beds.ac.uk/10.1016/j.geoderma.2015.03.008.

This should be used to discuss your found results concerning amount and effects of stand types on carbon distribution und carbon stocks. As you have only data in the top soil till 30 cm, you have to point at this fact prominently as it reduces the capabilities of a “total” carbon stock estimation.

2. You present data for forest soils. In your map you show values across the whole area of South Korea. This is not possible, as your presented model is based on forests only. This should be reduced to forests!

In Detail:

Abstract: please add that you present data for the top soil -30cm.

Abstract: add mean data of the C-stocks

Line 64: instead of “quantity” you mean “change” ?

Study area: add variabilities of temperature and precipitation, so that the reader can imagine the variability within South Korea

line 101: for instance … class V. this sentence is not important

figure 1: map is too small and can hardly be read.

Lines 128: calculation of carbon stocks is unclear: can you add the formula?

Table 1: unclear unit for bulk density (t d.m. m-3): Mg m-3 (?)

Results and discussion: see general point 1: compare your values with other countries / regions

Line 179/180: the carbon fixation potential of litter is very low, as it is very labile and can be decomposed fastly. I see the “fixation effect” very limited!

Lines 192/193: Where is the difference between the cited study and yours? Discuss differences!

3.2. soil and litter carbon stocks: more fundamental literature review needed!

Line 216: difference between class I and II is not significant!

Line 223: are tropical soils comparable with temperate sites of South Korea?

Line 253: in which context did Chen et al. report predictors (as well as Nanko)?

3.2.2. forest soil carbon map: please avoid regional names like  “Jeju” and “Gangwon”, as many people around the world might not know this. Can you describe it like “region in northwest” or “Island south of Korea mainland” or highlight it in the map.

Lines 280ff: this is very unclear, and the reference to regional details is not clear.

Line 288: “tier 2 levels”: what does this mean?

Line 287 ff: this is not a result, but a political advise. This could be part of the conclusions

Conclusions: this has to be checked ttally. At the moment you mainly repeat results. You should give conclusions on how you assess the outcome of your study. What can be learned for future studies, what is still needed? What can you derive for the GHG-inventories and reports?

Author Response

November 7. 2020

Dear reviewer 1:

We would like to submit the revised manuscript entitled “Assessing the carbon storage of soil and litter from national forest inventory data in South Korea” to be considered for publication as a communication in Forests.

We have responded to each comment raised by reviewers, and the manuscript has been revised accordingly. We also have found minor errors and typos in previous wording, which were corrected the manuscript. The revisions in the manuscript are in red font. We hope that our responses and revisions are acceptable.

All the co-authors have read this revised version of the manuscript, and approved its resubmission to Forests. We confirm that this manuscript has not been submitted elsewhere in part or in entirety and is not under consideration by another journal. We look forward to hearing from you.

Best regards,

Sunjeoung Lee
Division of Forest Industry
National Institute of Forest Science
Seoul 02455
Tel: +82-2-961-2833
Fax: +82-2-961-2839
[email protected]

 
[Response to reviewer 1]

We appreciate your review of our manuscript. Prepared are the responses to your comments and the revised manuscript in accordance with these comments. Revisions to our manuscript are indicated in red font.

Comment 1
The presentation would benefit by including further international publications, which deal with carbon stocks in forests soils, especially in temperate regions. There is important research from Europe, e.g.:

Gruneberg E., Schoning I., Riek W., Ziche D., Evers J. (2019) Carbon Stocks and Carbon Stock Changes in German Forest Soils. In: Wellbrock N., Bolte A. (eds) Status and Dynamics of Forests in Germany. Ecological Studies (Analysis and Synthesis), vol 237. Springer, Cham. https://0-doi-org.brum.beds.ac.uk/10.1007/978-3-030-15734-0_6

Vanguelova, E.I., Bonifacio, E., De Vos, B. et al. Sources of errors and uncertainties in the assessment of forest soil carbon stocks at different scales?review and recommendations. Environ Monit Assess 188, 630 (2016). https://0-doi-org.brum.beds.ac.uk/10.1007/s10661-016-5608-5

Bruno De Vos, Nathalie Cools, Hannu Ilvesniemi, Lars Vesterdal, Elena Vanguelova, Stefano Carnicelli, Benchmark values for forest soil carbon stocks in Europe: Results from a large scale forest soil survey, Geoderma, Volumes 251?252, 2015, Pages 33-46, ISSN 0016-7061, https://0-doi-org.brum.beds.ac.uk/10.1016/j.geoderma.2015.03.008.

This should be used to discuss your found results concerning amount and effects of stand types on carbon distribution und carbon stocks. As you have only data in the top soil till 30 cm, you have to point at this fact prominently as it reduces the capabilities of a “total” carbon stock estimation.

Response 1
Thank you for your specific comments in the attachment file. They were implemented throughout the manuscript.

Line 59-61 “Germany also reported national GHG inventory using the NFI data to estimate carbon stocks of all carbon pools (living biomass, soil, and dead organic matter for national GHG inventory report [14].”

Line 208-211 “The tree species could bring about a major impact in soil fauna activity and related incorporation of litter into the soil, possibly changing the inputs of organic layer material to upper mineral soil [44]. Moreover, root biomass and turnover rate of tree species would influence the residual carbon in from the litter to soil [44]”

Line 217-223 “However, soil carbon stocks also made difference in site conditions and soil texture. Coniferous forests had small soil carbon pools, while deciduous forests such as beech forests had large soil carbon pools. However, it varied depending on the site conditions where the species dominate [48,49]. Another study reported that loamy soil had higher carbon stocks under deciduous forest compared to coniferous forest. In contrast, soils from base-poor consolidated bedrock had higher carbon stocks under coniferous forests compared to deciduous forests [44].
”

Line 250-253 “. In case of temperate forests, no value difference was observed between tree biomass and soil carbon stocks [44]. Aging forests in steady state of carbon cycle have lower potential to carbon fixation than soils of younger forests, and it may be attributed to a loss of organic matter following management disturbance [55].”

Line 282-285 “This would be attributed to the difference in materials and methods. De Vos et al. [56] reported that soil type and tree species were major predictor for forest floor carbon stocks using boosted regression tree model. For topsoil carbon stocks, soil type, mean air temperature and precipitation were major predictor for mineral soil carbon stocks.”

Line 305-313 “Our results were lower than previous study in temperate forests. Wellbrock et al. [60] reported that carbon stock of German forests was 19.0 tC ha-1 in organic layer, 55.6 tC ha-1 in mineral soil to 30cm. De Vos et al. [56] reported that soil organic carbon stocks to 30cm of European forests was 71.3 tC ha-1, there were discrepancies among reference soil groups. The difference in the carbon stocks in forests among the countries might be due to the differences in parents soil material, mean temperature and precipitation, forest stand status such as age class, growing stocks, and tree species. Different scales for measuring, quantification, the sample size could be a difference in carbon stocks of soil organic carbon by countries as well [61].”

Line 336-339 “However, we used an ordinary kriging methodology for the carbon stocks map of forest soil and litter. In order to improve and accurate this map, it is necessary to improve mapping method. Using accurate forest cover and soil type maps while deciding appropriate scaling up method would aid in accomplishing such goal in the future [61].”

Comment 2
You present data for forest soils. In your map you show values across the whole area of South Korea. This is not possible, as your presented model is based on forests only. This should be reduced to forests!

Response 2
We really appreciate for your detailed comments. As you suggested, we have revised our manuscript in Figure 4 in Line 304-305.

Comment 3
Abstract: please add that you present data for the soil at 0-30cm.

Response 3
I appreciate the feedback. We have revised our manuscript as suggested;

Line 14 “Materials and Methods: This study was conducted to assess soil at 0-30 cm”

Comment 4
Abstract: add mean data of the C-stocks

Response 4
Thank you for your specific comment. We have revised our manuscript as advised.

Line 32 “carbon stocks”

Comment 5
Line 64: instead of “quantity” you mean “change” ?

Response 5
Thank you for your specific comments in the attachment file. We have changed the diction accordingly as following:

Line 69 “However, the change of carbon stocks in soil, dead…”

Comment 6
Study area: add variabilities of temperature and precipitation, so that the reader can imagine the variability within South Korea

Response 6
Thank you for your specific comments in attachment file. Additional variabilities have been added as suggested.

Line 93-95 “The mean annual precipitation ranges from 1,000 mm to 1,800mm in southern part of South Korea and from 1,100 mm to 1,400 mm in the central part of South Korea. The mean annual temperature ranges from 10 to 16 ℃ except in the high mountain areas [29].”

Comment 7
line 101: for instance … class V. this sentence is not important

Response 7
Thank you for your specific comments in attachment file. We have removed such detail from our manuscript at (Line 109)

Comment 8
figure 1: map is too small and can hardly be read.

Response 8
Thank you for your specific comments in attachment file. We have changed Figure 1 implementing your suggestion.

Comment 9
Lines 128: calculation of carbon stocks is unclear: can you add the formula?

Response 9
Thank you for your specific comments in attachment file. Per your feedback, the formula has been added.

Line 138
Soil carbon stocks (t C 〖ha〗^(-1) )=∑_(horizon=1)^3▒BD˟ (1-frag) ˟ CC ˟ D
where BD is bulk density (Mg m3), frag is % contents of coarse fragments/100, CC is carbon contents (%), D is depth of soil (cm), and horizon is soil depth layer which are notated by numbers from 1 to 3, each number signifying the depths of 0-10cm, 10-20cm, and 20-30cm respectively.
Line 145
Litter carbon stocks ( t C 〖ha〗^(-1) )=∑_(horizon=1)^2▒〖DW ˟ CF〗
where DW is dry weight of litter (t ha-1) and CF is % carbon contents/100. When horizon equals to 1, the equation calculates litter carbon stocks for L horizon, and when horizon equals to 2, it computes the litter carbon stock of FH horizon.

Comment 10
Table 1: unclear unit for bulk density (t d.m. m-3): Mg m-3 (?)

Response 10
Thank you for your specific comments in attachment file. We have changed our manuscript as your comment suggested (Table 1).

Comment 11
Results and discussion: see general point 1: compare your values with other countries / regions

Response 11
Thank you for your specific comments in the attachment file. They were revised throughout the manuscript as mentioned above at “Response 1.”

Comment 12
Line 179/180: the carbon fixation potential of litter is very low, as it is very labile and can be decomposed fastly. I see the “fixation effect” very limited!

Response 12
Thank you for your specific comments in attachment file. We have removed this portion from our manuscript (Line 196).

Comment 13
Lines 192/193: Where is the difference between the cited study and yours? Discuss differences!

Response 13
Thank you for your specific comments in attachment file. We have changed our manuscript according to your comment.

Line 201: “Previous study in South Korea reported that soil carbon stocks were …”

Comment 14
3.2. soil and litter carbon stocks: more fundamental literature review needed!

Response 14
Thank you for your specific comments in the attachment file. They were revised throughout the manuscript as mentioned above at “Response 1.”

Comment 15
Line 216: difference between class I and II is not significant!

Response 15
Thank you for your specific comments in attachment file. We have changed our manuscript to reflect your remark.

Line 241-242 “This study observed a higher carbon stock in the age class I than in the age class II even if there is no statistically significant difference.”

Comment 16
Line 223: are tropical soils comparable with temperate sites of South Korea?

Response 16
The statement was not intended to compare values, but to present a previously recorded case where the change in carbon stocks due to stand maturation occurred in tropical forest. New literature was cited for accuracy.

Line 250-253 “In case of temperate forests, no value difference was observed between tree biomass and soil carbon stocks [44]. Aging forests in steady state of carbon cycle have lower potential to carbon fixation than soils of younger forests, and it may be attributed to a loss of organic matter following management disturbance [55].”

Comment 17
Line 253: in which context did Chen et al. report predictors (as well as Nanko)?

Response 17
Thank you for your specific comments in attachment file. We have added our manuscript to clarify the meaning of the sentence.

Line 285~288 “Chen et al. [18] reported that the most important predictors, ranked from the highest to lowest, are land cover, parent material, net primary production, elevation, mean annual temperature, mean annual precipitation, erosion rates, topographic wetness index, soil type, and slope using RF modeling.”

Comment 18
3.2.2. forest soil carbon map: please avoid regional names like “Jeju” and “Gangwon”, as many people around the world might not know this. Can you describe it like “region in northwest” or “Island south of Korea mainland” or highlight it in the map.

Response 18
Thank you for your specific comments in attachment file. We have changed our manuscript to clarify the meaning of the sentence.

Line 313-317 “The map shows that Gangwon-do, the north-eastern part of South Korea, and Jeju-do, the southern island in South Korea, carry a large quantity of soil carbon stocks. In the case of Gangwon-do, there are large growing stocks in forests. Jeju-do is a volcanic island formed by continental intraplate volcanism [62], which could explain the reason of the great soil carbon stocks in Jeju-do, the southern island in South Korea.”

Comment 19
Lines 280ff: this is very unclear, and the reference to regional details is not clear.

Response 19
Thank you for your specific comments in attachment file. We have changed our manuscript for a better illustration.

Line 321-323 “. This map demonstrated a similar trend to the biomass resource map in the South: there were many biomass resources in the north-eastern part, east-southern part, and southern-central part [65]”

Comment 20
Line 288: “tier 2 levels”: what does this mean?

Response 20
Such tiers are for the GHG inventory reporting system, and data set used for the inventory report can be classified from tier 1 to 3, according to the level.

Comment 21
Line 287 ff: this is not a result, but a political advise. This could be part of the conclusions

Response 21
We have determined that such statement is an implication based on the results and discussion found in current manuscript, and deemed it to be appropriate part of the discussion. However, this has been added in conclusion portion of the manuscript as well.

Comment 22
Conclusions: this has to be checked ttally. At the moment you mainly repeat results. You should give conclusions on how you assess the outcome of your study. What can be learned for future studies, what is still needed? What can you derive for the GHG-inventories and reports?

Response 22
Thank you for your specific comments in attachment file. We have changed our manuscript to clarify the meaning of the sentence.

Line 352-363 “Our findings will provide a more detailed information on litter and soil carbon stocks, thereby facilitating the understanding of forest carbon storage in South Korea. A few limitations, however, were seen. We were only able to utilize the data sets gathered over four years, a year short of full grid sampling cycle of the NFI. Including a full set of the data will allow not just for a more accurate estimation of carbon stocks in forest soil, but also for identification of change in them in the near future. Another flaw is that only one methodology was applied to map the carbon stocks in forest soil and litter. To obtain precise information on them requires to compare appropriate scaling-up tools. These drawbacks notwithstanding, the methods used in this study to estimate and map carbon stocks in forest litter and soil could be adopted in future national GHG inventory reports for tier 2 levels. All carbon pools can also be assessed by the approaches to achieve accuracy and completeness in the reports. Moreover, soil and litter carbon maps will be of great use for spatial soil carbon stocks at a national level, the data of which will eventually be utilized at a global level.”

Author Response File: Author Response.docx

Reviewer 2 Report

The subject of the paper fits the profile of "Forests" journal. The publication “Assessing the carbon storage of soil and litter from national forest inventory data in South Korea” presents some interesting and important studies. The presented manuscript is well prepared and has a proper structure. Overall impression is very good.

However, a fundamental question arises for the Authors, is it possible to speak of soil carbon stocks based on the data from the litter and the soil surface layer - 0-30 cm? In the 20-30 cm layer, significant organic carbon stocks were found in all studied soils of three forest types, which suggests that organic carbon can be present in deeper parts of soil profiles. This question is debatable.

 Article is suitable for publication after amendments. Comments and suggestions for Authors are given below:

• line 29, correct as “carbon stocks”,
• in line 90 should be “parent soil material”,
• in line 91-94 the Authors use the Soil Taxonomy (USA) units first, then go on to determine the local terminology of soil profiles. What is immature soil? Eroded soil is not the soil type. It is inconsistent. I think that for a global audience it would be best to use WRB (World reference base for soil resources soil) nomenclature, if such data are of course available,
• figure 1, it is completely unreadable, especially the description of the legend,
• line 116-127, it is not clear whether the analysis presented here are normally done as part of the NFI program, or if they were performed for the purposes of this paper,
• line 119, instead of “mineral soils” it should be “fine earth fractions”,
• line 121 (which applies to all manuscript), I propose to change the L, FH “layer” to “horizon”, because depth was not taken into account but their development degree,
• line 127, “elemental analyzer”, but by what method (oxidation?), what apparatus name?
• table 1, “Corse (or rock) fragments content (%)” or “Soil skeleton (%)”
• line 149, please explain the abbreviation DBH, also other abbreviations in paper, e.g. RMSE (root-mean-square error?) – line 240,
• figure 3, please replace (a) with (b) in the description or on the graphs,
• table 4, Why uses “,” and not “.” next to numbers, do you need such accuracy as 3 decimal places, e.g. for a height of 16 m, 84 cm and 2 mm?
• figure 4, like in figure 1.

 Article is suitable for publication after correction (minor revision).

Author Response

November 7. 2020

Dear reviewer 2:

We would like to submit the revised manuscript entitled “Assessing the carbon storage of soil and litter from national forest inventory data in South Korea” to be considered for publication as a communication in Forests.

We have responded to each comment raised by reviewers, and the manuscript has been revised accordingly. We also have found minor errors and typos in previous wording, which were corrected the manuscript. The revisions in the manuscript are in red font. We hope that our responses and revisions are acceptable.

All the co-authors have read this revised version of the manuscript, and approved its resubmission to Forests. We confirm that this manuscript has not been submitted elsewhere in part or in entirety and is not under consideration by another journal. We look forward to hearing from you.

Best regards,

Sunjeoung Lee
Division of Forest Industry
National Institute of Forest Science
Seoul 02455
Tel: +82-2-961-2833
Fax: +82-2-961-2839
[email protected]

 
[Response to reviewer 2]
We appreciate your review of our manuscript. Prepared are the responses to your comments and the revised manuscript in accordance with these comments. Revisions to our manuscript are indicated in red font.

Comment 1
However, a fundamental question arises for the Authors, is it possible to speak of soil carbon stocks based on the data from the litter and the soil surface layer - 0-30 cm? In the 20-30 cm layer, significant organic carbon stocks were found in all studied soils of three forest types, which suggests that organic carbon can be present in deeper parts of soil profiles. This question is debatable.

Response 1
Thank you for your specific comments in attachment file. They were implemented throughout the manuscript.

Comment 2
line 29, correct as “carbon stocks”

Response 2
We really appreciate for your detailed comments. As you suggested, we have revised our manuscript as follows;

Line 32 “carbon stocks”

Comment 3
in line 90 should be “parent soil material”,

Response 3
As you suggested, we have revised our manuscript as follows;

Line 96 “parent soil material”

Comment 4
in line 91-94 the Authors use the Soil Taxonomy (USA) units first, then go on to determine the local terminology of soil profiles. What is immature soil? Eroded soil is not the soil type. It is inconsistent. I think that for a global audience it would be best to use WRB (World reference base for soil resources soil) nomenclature, if such data are of course available,

Response 4
Thank you for your specific comment. Like those of Japan and North Korea, South Korea’s forest soil has its own soil classification system according to the values of productivity in forests. The forest soil map used in this study was prepared according to the classification system of South Korea, and therefore, the subclassification of forest soil could not meet the international standards, such as WRB. However, we have added the information to our manuscript as advised.

Line 98-99 “South Korea developed independent soil classification system for forest soil due to importance of forest productivity.”

Comment 5
figure 1, it is completely unreadable, especially the description of the legend,

Response 5
Thank you for your specific comments in attachment file. We have changed our manuscript according to your suggestion (Figure 1).

Comment 6
line 116-127, it is not clear whether the analysis presented here are normally done as part of the NFI program, or if they were performed for the purposes of this paper,

Response 6
Thank you for your specific comments in attachment file. We have changed our manuscript according to your feedback.

Line 123 “Sampling and analysis of soil and litter were performed in NFI and FHM survey.”

Comment 7
line 119, instead of “mineral soils” it should be “fine earth fractions”,

Response 7
Thank you for your specific comments in the attachment file. We have changed the dictions accordingly as following:

Line 127: “fine earth fractions”

Comment 8
line 121 (which applies to all manuscript), I propose to change the L, FH “layer” to “horizon”, because depth was not taken into account but their development degree,

Response 8
Thank you for your specific comments in attachment file. They were implemented throughout the manuscript.

Comment 9
line 127, “elemental analyzer”, but by what method (oxidation?), what apparatus name?

Response 9
Thank you for your specific comments in attachment file. We have changed our manuscript to reflect your remark.

Line 135: “analyzer (vario Macro, Elementar Analysensystme, Germany) [35].”

Comment 10
table 1, “Corse (or rock) fragments content (%)” or “Soil skeleton (%)”

Response 10
Thank you for your specific comments in attachment file. We have changed our manuscript implementing your comment (Table 1).

Comment 11
line 149, please explain the abbreviation DBH, also other abbreviations in paper, e.g. RMSE (root-mean-square error?) ? line 240,

Response 11
Thank you for your specific comments in attachment file. We have already explained the DBH in Line 107. However, we changed our manuscript as your comment regarding the RMSE (Line 269).

Comment 12
figure 3, please replace (a) with (b) in the description or on the graphs,

Response 12
Thank you for your specific comments in attachment file. We have changed the description (Figure 3).

Comment 13
table 4, Why uses “,” and not “.” next to numbers, do you need such accuracy as 3 decimal places, e.g. for a height of 16 m, 84 cm and 2 mm?

Response 13
The comma was used to distinguish two numerical values, and is not a typo for a decimal point.

Comment 14
figure 4, like in figure 1.

Response 14
Thank you for your specific comments in attachment file. We have changed the description for (Figure 4).

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Thank you very much for considering my comments on your manuscript!

In this stage i can support a publication.

There are only two little comments:

figure 1: This graph is very small. is the print quality better than this?

figure 4: i suggest to add "forest soils" in the caption.

Author Response

[Reviewer 1]

We appreciate your comments of our manuscript. Prepared are the responses to your comments and the revised manuscript in accordance with these comments. Revisions to our manuscript are indicated in red font.

Comment 1
Figure 1: This graph is very small. Is the print quality better than this?

Response 1
Thank you for your detailed comments. As you suggested, we have revised our Figure 1 resolution (300dpi → 1000 dpi).

Comment 2
Figure 4: I suggest to add “forest soils” in the caption.

Response 2
We really appreciate for your specific comments in attachment file. The specific information was implemented throughout the manuscript.
Line 324-325 “Figure 4 Map of carbon stocks in (a) soil at 0–30 cm, (b) soil at 0–30 cm and litter in South Korean forests”
Line 86, 105, 342 “South Korea” →”South Korean forests”

Author Response File: Author Response.docx