Review Reports - Performance Analysis of Log Extraction by a Small Shovel Operation in Steep Forests of South Korea

Round 1

Reviewer 1 Report

It was a pleasure reading this nicely written paper. The manuscript presents appropriate and useful work, it is most interesting.

I only have some minor suggestions for possible improvement and namely:

Tile and keywords have different goal and therefore, I suggest to select keyword that are not already in the title (small shovel and log extraction). Choosing the right keywords will help other researchers find and share your article. Function of keywords should be to supplement the information given in the title. I suggest to replace small shovel and log extraction with different words

Line 53: I suggest to rephrase the part "conifers being the dominant species, followed by Korean red pine...." Species you reported are conifers therefore, it could be "namely" and not "followed". Please verify

Line 109-120. First you declared that no information was available on delay times and then you wrote that you included machine delays. Please, can you specify?

Figure 3. I'm not sure this is relevant. You already mentioned this in the text.

Author Response

Point 1: Tile and keywords have different goal and therefore, I suggest to select keyword that are not already in the title (small shovel and log extraction). Choosing the right keywords will help other researchers find and share your article. Function of keywords should be to supplement the information given in the title. I suggest to replace small shovel and log extraction with different words

Response 1: We changed ‘small shovel’ and ‘log extraction’ with different words. (in red)

-‘small shovel’ to excavator with a log grapple

-‘log extraction’ to cut-to-length extraction

Point 2: Line 53: I suggest to rephrase the part "conifers being the dominant species, followed by Korean red pine...." Species you reported are conifers therefore, it could be "namely" and not "followed". Please verify

Response 2: We changed it, as suggested. (in red)

Point 3: Line 109-120. First you declared that no information was available on delay times and then you wrote that you included machine delays. Please, can you specify?

Response 3: We have no information about machine delays during small-shovel operation. In addition, follow-up data include machine operation and idle time, and we can not divide. Therefore, we calculate only the cost per SMH, which is included productive, delay, and warm-up cost. Thus, We do not know about cost per PMH.

Point 4: Figure 3. I'm not sure this is relevant. You already mentioned this in the text.

Response 4: We deleted in Figure 3 description. (in red)

Author Response File: Author Response.docx

Reviewer 2 Report

I congratulate the authors for writing a nice and dense manuscript on an interesting topic and with informative results. However, the manuscript needs a revision before publishing because of the following deficits:

· There are too many errors in the discussion of your results. I strongly suggest (demand may be a better word) that the Results and Discussion be split up into two separate sections. This division will allow the authors to present their somewhat illogical results (which are most probably a product the vast amounts of "noise" that manually collected follow-up data often brings with it), and then discuss their validity in the face of common knowledge of forest operations.

· Extraction distance: what exactly is the authors' definition? There are numerous somewhat contradictory definitions, c.f. Lines 22-23 and Line 237 with Lines 99-100 and 107-108. Extracting logs to the roadside is hugely different than extracting to a skid trail. Skid trails implies that you need terrain vehicles (like tractors, skidders or forwarders) to finish off the log extraction, while trucks can be used from the roadside onwards. Presently, readers cannot be sure what extraction distance exactly is, and that is very bad (see next bullet). A drawing (visual definition) would partly aid in solving the problem.

· No credible study has previously shown that log extraction productivity increases with extraction distance. This thinking is illogical since it is a physical law that it takes more time to extract logs the farther the distance is (ceteris paribus). But Time Consumption (which is the inverse of productivity) does increase with extraction distance. Please study your reference #42 thoroughly (you will see that you have misunderstood it! Yes, time consumption is positively dependant on distance, but productivity is negatively dependant), and find more suitable (ie. reputable, valid, and reliable) references than your ref. #43 for this fundamental fact.

· The authors’ show (Fig. 8) that productivity does increase with extraction distance. Here, extraction distance is probably a proxy variable for eg. total tract size/total stand volume (this latter variable should be included in your analysis. The reason: productivity per SMH almost always increases with increasing total harvested volume because the effect of relocation time, upstart time, etc. decreases with increasing harvested volume). Please reanalyze your data. Or could it be the lack of a rigorous definition of extraction distance that is the problem (ie different operators measured the distance differently)?

· On a similar topic, please rework your Lines 184-187. Your explanations are neither clear nor helpful for the reader.

· Most often, the authors' choose to compare their Shovel Logging-results with results from other extraction systems (tractor, skidding, forwarding). This choice is often wrong because the productivity influencing factors of small excavators are sometimes different from those of forwarders, tractors, etc. Please compare your results with previous studies of excavators working as shovel loggers/hoe chuckers (there are previously published studies available).

· Your present productivity function should be either excluded or reworked so that it is not solely reliant on an illogical proxy variable (Table 3). Try testing “total harvested volume”. Or choose a confidence level of 90%.

· The second sentence in the captions for Figures 4, 5, 7, 8, 9 are often dead wrong. There is absolutely no correlation in Figures 7 and 9, let alone moderate correlation. And your correlation in Figure 8 is more than moderate!

· The manuscript needs less descriptions about correlation between stand density, Dbh, and average stem volume. Fig 6 has no value in this manuscript, and should be removed.

· The manuscript needs more methods descriptions = definitions of work tasks, system descriptions, machine descriptions, etc.

o What typical manufacturer of excavators, typical boom lengths, grapple types?

o Please provide a figure of how the excavator works.

o How many logs does the boom reach per stationary point?

o Which is the excavator’s travel direction in terms of the slope direction?

o The extraction distances are very short by international standards (30-70 m!). Please elaborate with a paragraph in the intro about the average road density in Korea, typical extraction distances, etc).

o Line 134: Hauling distance = what distance is that? Tractors? Trucks?

o All of the above is essential information if international readers are to understand your results.

· There are many other errors that need to be fixed: SI units only in Table 2, Fig 10, language in the conclusions, Patents? (there are none), etc. Please have your coauthors and colleagues critically review your revised manuscript before sending it in again.

Author Response

Point 1: There are too many errors in the discussion of your results. I strongly suggest (demand may be a better word) that the Results and Discussion be split up into two separate sections. This division will allow the authors to present their somewhat illogical results (which are most probably a product the vast amounts of "noise" that manually collected follow-up data often brings with it), and then discuss their validity in the face of common knowledge of forest operations.

Response 1: Thank you for your suggestions. But, we would like to write the result and discussion into one section, since it is first study to introduce “small-shovel performance in various sites” to the world. So, we want to report what the results mean in small-shovel extraction activity in South Korea.

Point 2: Extraction distance: what exactly is the authors' definition? There are numerous somewhat contradictory definitions, c.f. Lines 22-23 and Line 237 with Lines 99-100 and 107-108. Extracting logs to the roadside is hugely different than extracting to a skid trail. Skid trails implies that you need terrain vehicles (like tractors, skidders or forwarders) to finish off the log extraction, while trucks can be used from the roadside onwards. Presently, readers cannot be sure what extraction distance exactly is, and that is very bad (see next bullet). A drawing (visual definition) would partly aid in solving the problem.

Response 2: We defined extraction distance in line 96-98 and changed skid trail to roadside. (in red) “We defined extraction distance in small-shovel operation as starts when the small-shovel leaves the forest road or landing area and ends when it reaches the landing.”

Point 3: No credible study has previously shown that log extraction productivity increases with extraction distance. This thinking is illogical since it is a physical law that it takes more time to extract logs the farther the distance is (ceteris paribus). But Time Consumption (which is the inverse of productivity) does increase with extraction distance. Please study your reference #42 thoroughly (you will see that you have misunderstood it! Yes, time consumption is positively dependant on distance, but productivity is negatively dependant), and find more suitable (ie. reputable, valid, and reliable) references than your ref. #43 for this fundamental fact.

Response 3: We changed this paragraph in line 165-177. (in red)

“Another important variable that influences SS productivity was the extraction distance. Both Ghaffariyan et al. [39] and Strandgard et al. [40] studies found that productivity was significantly related to extraction distance, since the load travel time accounted for over one quarter of the variation in cycle time. In addition, extraction productivity increased with a decrease in extraction distance [41, 42, 43]. However, this study implied that an increased extraction distance would be positively and significantly correlated with SS productivity (p< 0.001; r=0.8262; Fig. 87). The operation of SS in South Korea, unlike the ground-based extraction method, is to use gravity. During the operation, throwing and rolling activity, which is to transfer logs from felling area down to the landing area, may associate with a large number of logs and longer distance, but the load travel time was not affected. Thus, productivity of SS depends on the number of logs per extraction cycle and extraction distance.”

Point 4: The authors’ show (Fig. 8) that productivity does increase with extraction distance. Here, extraction distance is probably a proxy variable for eg. total tract size/total stand volume (this latter variable should be included in your analysis. The reason: productivity per SMH almost always increases with increasing total harvested volume because the effect of relocation time, upstart time, etc. decreases with increasing harvested volume). Please reanalyze your data. Or could it be the lack of a rigorous definition of extraction distance that is the problem (ie different operators measured the distance differently)?

Response 4: We changed this paragraph in line 165-177. (in red)

Point 5: Most often, the authors' choose to compare their Shovel Logging-results with results from other extraction systems (tractor, skidding, forwarding). This choice is often wrong because the productivity influencing factors of small excavators are sometimes different from those of forwarders, tractors, etc. Please compare your results with previous studies of excavators working as shovel loggers/hoe chuckers (there are previously published studies available).

Response 5: Yes, but we did not compare productivity with previous studies (evaluation productivity of tractor, skidding, and forwarding). We would like to use to explain “why this trend happens?”.

Point 6: Your present productivity function should be either excluded or reworked so that it is not solely reliant on an illogical proxy variable (Table 3). Try testing “total harvested volume”. Or choose a confidence level of 90%.

Response 6: We explained why the extraction distance affected line 165-177. (in red) So, we think extraction distance is one of effective variable in SS operation.

Point 7: The second sentence in the captions for Figures 4, 5, 7, 8, 9 are often dead wrong. There is absolutely no correlation in Figures 7 and 9, let alone moderate correlation. And your correlation in Figure 8 is more than moderate!

Response 7: We changed the second sentence as your comments in Figure 7, 8, 9. (in red)

Point 8: The manuscript needs less descriptions about correlation between stand density, Dbh, and average stem volume. Fig 6 has no value in this manuscript, and should be removed.

Response 8: We deleted the Fig 6.

Point 9: The manuscript needs more methods descriptions = definitions of work tasks, system descriptions, machine descriptions, etc.

o What typical manufacturer of excavators, typical boom lengths, grapple types?, Please provide a figure of how the excavator works.

Response : We used excavator in many manufacture and SS is only changed excavator head. Therefore, we added in Figure 1 description about boom length and grapple types. Also we added picture for excavator work. (in red)

o How many logs does the boom reach per stationary point?

Response : We have limitation with this information. But the SS work covered 30 m length.

o Which is the excavator’s travel direction in terms of the slope direction?

Response : Yes excavator’s travel direction is slope direction. We also report reference # 10, 28 in line 106-107 to description SS operation.

Response : The average road density is 108 m/ha (ranged from 32 to 188 m/ha) in this study harvest unit NOT Korea.

o Line 134: Hauling distance = what distance is that? Tractors? Trucks?

Response : We changed extraction distance in line 144. (in red)

o All of the above is essential information if international readers are to understand your results.

Response : Thank you for your comment.

Point 10: There are many other errors that need to be fixed: SI units only in Table 2, Fig 10, language in the conclusions, Patents? (there are none), etc. Please have your coauthors and colleagues critically review your revised manuscript before sending it in again

Response 10: Yes, we revised manuscript with co-authors and colleagues.

Author Response File: Author Response.docx

Reviewer 3 Report

The lanugage needs extensive editing. I am sorry to say I do not have time enough to comment on all statements that are in need of edition, but large parts of the

manuscript are very confusing due to poor language. This alsomakes impossible to do a proper review. So: please rewrite the entire manuscript to be a lot more

clear and to the point. Avoid empty statements.

Please also describe the context in which the showel logging is taking place. I assume this log extraction work is part of a supply chain starting at the stump

and ending at the roadside. What is the other parts of this chain? Do you have a road density where 60 metre extraction distance is enough to get the logs to a

roundwood truck?

Abstract:
Line 17: "..improving productivity over the world.." I'm sorry but i do not get the message.
Line 18: The follow up method is not such an established method. Consider rewriting to something like: ".. we conducted a study using follow-up data to

determine...".
Line 19 - 20: Your language is a bit blurrying. The impact of related variables is found by modelling the productivity and using log and site characteristics like

log volume, extraction distance and slope percentage as explanatory variables. Please rewrite these lines to clarify your message.
Line 22: What is forest level? I think you better drop the term. You better clarify in the methods brief (line 18-19) what was your observation unit.
Line 22-23: In my opinon it would be even more interesting if your results was expressed like time consumption per m3 per extraction distance. E.g. hours m3^-1

m^-1. Or, you could write in your initial material and methods brief (line 18-19) the working conditions; range of extraction distance, slope percentage and log

sizes in your study.
Line 23: The costs were 4.37 and 17.66 respectively. In the conclusions this was set to be the range of extraction costs. So: what kind of numbers are these

numbers really?

Line 26-28: Poor language - I do not understand the message. Please rewrite.

Line 34: Logging operation and primary transportation: I'm not sure these are equivalent terms. I believe a logging operation includes both felling, processing,

and extraction to roadside, where the latter is primary transportation.

Line 36-37: Poor language - i do not understand the message. Please rewrite.
Line 39-41: Poor grammar - singular|plural confusion.

Line 46: "In another example" - what was the first example?
Line 46: The study method do not by it self limit the data availability nor does it necessarily generate unsafe working conditions. But indeed data collection is

more costly - as researchers has to do substantial fieldwork to get the data.
Line 46: Reference 16 - Strandgard Mitchell: This paper examines the ability of a automated data collection system to gather data similar to a time- and motion

study. It does not claim traditional methods provide too limited data.
Line 48: Ref 17, Siren Aaltio: In this paper the data collection was organized for follow up studies, i.e. using templates for operators for separating time

consumption into productive time and other time categories as well as productivity.
Line 42 - 49: Please move this to the methods chapter, and rewrite and be more to the point: what are the pros and cons for each of these two methods. Why did you

choose one of them. Economical limitations, availability of data, are still fair motives to choose the method you have choosed.

Line 65-66: These statements are not linked. The most cost-efficient logging method would normally be the preferede one - irrespective of the value of the

product?

Line 76: Various types of forest? It is unclear what is one type and what is another type. Another place it was mentioned to be conifer / deciduous / mix. In your dataset (Table 1) does not, as far I can see, indicate various types of forest.
Line 75 - 81: Essential part of the manuscript, and still very confusing. Please clarify both the general and the specific research questions. Then if the same dataset is used to answer all RQ's you mention the dataset and datasource only once.

Line 103 - 105: The methods used to characterize each harvest unit should be described here

Line 106-107: The two processes are not separated later on in the manuscript?

Line 167 - 169: I have no idea what is the message here
Line 170 - 171: I have no idea what is the message here

Conclusions
Line 236-237: I suggest to skip empty statements. You do not need a study to find that the productivity will vary across harvest units.
Line 239: These costs are estimated costs according to your cost calculations. They are not direct observations from your study data. So I would suggest to link

your findings to your material. I.e. "According to the cost deduction the corresponding extraction costs were estimated to be in the range..."
Line 240: "statistically influenced" - i personally do not like this term - I suggest you rather point to variables "significantly affecting productivity" or

having "a significant impact on productivity".
Line 249: Very poor language. I am not sure what you intend to tell the audience
Line 249- 252: Poor language and statements. I.e. a larger range of tree volumes will probably widen the valid range of the model, but not improve the accuracy?

Author Response

Point 1: Please also describe the context in which the showel logging is taking place. I assume this log extraction work is part of a supply chain starting at the stump and ending at the roadside. What is the other parts of this chain? Do you have a road density where 60 metre extraction distance is enough to get the logs to a roundwood truck?

Response 1: SS operations in each unit were performed using a semi-mechanized system that employs a chainsaw for felling, limbing, and bucking trees into 2-4 m logs. Then SS operation utilized the gravity extraction technique, which involves throwing, rolling, and pushing logs, to move the logs to the roadside or landing area. This is the SS operation chain.

In addition, the average road density is 108 m/ha (ranged from 32 to 188 m/ha) in this study harvest unit NOT Korea. So, extraction distance (32-72 m) was enough to get the logs to a roundwood truck.

Point 2: Line 17: "..improving productivity over the world.." I'm sorry but i do not get the message

Response 2: We deleted the “over the world” and changed the “in steep slopes and in accessible sites” in Line 17. (in red)

Point 3: Line 18: The follow up method is not such an established method. Consider rewriting to something like: ".. we conducted a study using follow-up data to determine...".

Response 3: We changed it (in red) to “… the main objectives were to determine…” in Line 18.

Point 4: Line 19 - 20: Your language is a bit blurrying. The impact of related variables is found by modelling the productivity and using log and site characteristics like log volume, extraction distance and slope percentage as explanatory variables. Please rewrite these lines to clarify your message.

Response 4: We wrote the study area description in line 21 - 24. (in red)

Point 5: Line 22: What is forest level? I think you better drop the term. You better clarify in the methods brief (line 18-19) what was your observation unit.

Response 5: We wrote the study area description in line 21 - 24. (in red)

Point 6: Line 22-23: In my opinon it would be even more interesting if your results was expressed like time consumption per m3 per extraction distance. E.g. hours m3^-1 m^-1. Or, you could write in your initial material and methods brief (line 18-19) the working conditions; range of extraction distance, slope percentage and log sizes in your study.

Response 6: We wrote the study area description in line 21 - 24. (in red)

Point 7: Line 23: The costs were 4.37 and 17.66 respectively. In the conclusions this was set to be the range of extraction costs. So: what kind of numbers are these numbers really?

Response 7: We wrote the working conditions (DBH, slope, tree per hectare, extraction distance) in line 21 - 24. (in red)

Point 8: Line 26-28: Poor language - I do not understand the message. Please rewrite.

Response 8: We changed in line 30-32. (in red)

“Our findings provide insights into how stem size and extraction distance influences on SS’s performance and the predictive ability of productivity.”

Point 9: Line 34: Logging operation and primary transportation: I'm not sure these are equivalent terms. I believe a logging operation includes both felling, processing, and extraction to roadside, where the latter is primary transportation.

Response 9: Yes, Logging operation includes felling, skidding/yarding, processing and loading (Enache et al., 2016). However, the term logging operation is sometimes used narrowly to define as the extraction of logs to landings (Acar et al., 2010; Harrill, 2014). Further, primary transportation that move logs at stump to landing by various option (Grebner et al., 2013).

Point 10: Line 36-37: Poor language - i do not understand the message. Please rewrite.

Response 10: We changed in line 40-41. (in red)

“…, but can be extremely expensive and more time-consuming practice than felling and processing”

Point 11: Line 39-41: Poor grammar - singular|plural confusion.

Response 11: We changed “logging practices” to “logging practice”, and “limitations” to “limitation” in line 44-45. (in red)

Point 12: Line 46: "In another example" - what was the first example?

Response 12: The first example is time and motion study method.

Point 13: Line 46: The study method do not by it self limit the data availability nor does it necessarily generate unsafe working conditions. But indeed data collection is more costly - as researchers has to do substantial fieldwork to get the data.

Response 13: We changed as your comment in line 49-51. (in red)

“However, this approach has a limitation on data availability due to short period of data collection and high costs of field data collection”

Point 14: Line 46: Reference 16 - Strandgard Mitchell: This paper examines the ability of a automated data collection system to gather data similar to a time- and motion study. It does not claim traditional methods provide too limited data.

Response 14: We deleted reference 16. (in red)

Point 15: Line 48: Ref 17, Siren Aaltio: In this paper the data collection was organized for follow up studies, i.e. using templates for operators for separating time consumption into productive time and other time categories as well as productivity.

Response 15: Yes, but follow-up study is more accurate information than time and motion study method (Siren and Aaltio, 2003) in line 54. So we did not remove this reference.

Point 16: Line 42 - 49: Please move this to the methods chapter, and rewrite and be more to the point: what are the pros and cons for each of these two methods. Why did you choose one of them. Economical limitations, availability of data, are still fair motives to choose the method you have choosed.

Response 16: This paragraph is mainly about what are the pros and cons for each method: time and motion, and follow-up method. So, we do not move this to the methods chapter.

Point 17: Line 65-66: These statements are not linked. The most cost-efficient logging method would normally be the preferede one - irrespective of the value of the product?

Response 17: We deleted in line 69-70. (in red)

Point 18: Line 76: Various types of forest? It is unclear what is one type and what is another type. Another place it was mentioned to be conifer / deciduous / mix. In your dataset (Table 1) does not, as far I can see, indicate various types of forest.

Response 18: We added the information of stand types in Table 1. (in red)

Point 19: Line 75 - 81: Essential part of the manuscript, and still very confusing. Please clarify both the general and the specific research questions. Then if the same dataset is used to answer all RQ's you mention the dataset and data source only once.

Response 19: We rephrase this paragraph in line 82-88. (in red)

“Therefore, in this study, the overall objective was to determine the performance of SSs in various types of forest. In particular, this study sought to: (1) determine the productivity (m³/SMH) and costs (US $/m³) of extracting logs through the follow-up method, (2) establish the influential variables in SS extraction productivity, and (3) develop regression models to predict SS productivity. Further, the results of this study will lead to better-informed SS technology decisions and more efficient production of timber products.

Point 20: Line 103 - 105: The methods used to characterize each harvest unit should be described here

Response 20: We already described the characterize each harvest in line 90-103.

Point 21: Line 106-107: The two processes are not separated later on in the manuscript?

Response 21: Yes, but we would like to introduce SS operation process steps in line 115-117.

Point 22: Line 167 - 169: I have no idea what is the message here

Response 22: We rephrase this sentence in line 182-183. (in red)

“These studies found that the slope was not significantly impact on loaded travel time during extraction activities.”

Point 23: Line 170 - 171: I have no idea what is the message here

Response 23: We rephrase this sentence in line 184-186. (in red)

“This study showed that slope has little influence on SS productivity, since the throwing and rolling logs time may be considerably more than travel time.”

Point 24: Line 236-237: I suggest to skip empty statements. You do not need a study to find that the productivity will vary across harvest units.

Response 24: We deleted it in line 254-255. (in red)

Point 25: Line 239: These costs are estimated costs according to your cost calculations. They are not direct observations from your study data. So I would suggest to link your findings to your material. I.e. "According to the cost deduction the corresponding extraction costs were estimated to be in the range..."

Response 25: We changed it as your comment in line 258-259. (in red)

Point 26: Line 240: "statistically influenced" - i personally do not like this term - I suggest you rather point to variables "significantly affecting productivity" or having "a significant impact on productivity".

Response 26: We changed it “statistically influenced” to a significant impact in line 260 description. (in red)

Point 27: Line 249: Very poor language. I am not sure what you intend to tell the audience

Response 27: We deleted this sentence in line 271-272. (in red)

Point 28: Line 249- 252: Poor language and statements. I.e. a larger range of tree volumes will probably widen the valid range of the model, but not improve the accuracy?

Response 28: We deleted this paragraph in line 271-275. (in red). And we move and change the last sentence in line 267-269.

“Further study is needed using a broader and more updated range of data, with a tree volume greater than 0.6 m³, to develop applicable prediction model across South Korea.”

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

This article has the potential to be published, but not in its current form. Unfortunately, the authors have not sufficiently addressed my concerns regarding the previous review’s points # 1, 3, 4, 5, 6, 8, 9, 10. And the addresses to points # 2, 3 are grammatically incomprehensible (erroneous). Regarding point # 7, Figs 6 and 8 still have absolutely no correlation. Regarding point # 10, please fix all errors that I have pointed out.

Please address all my concerns without brushing aside their inherent meaning.

Author Response

Thank you very much for your time and thoughtful review of our manuscript. We appreciate your constructive comments, and we apologize that they were not sufficiently addressed in the first-round review. We have now significantly revised the article. Below, we have quoted your first-round comments and added new responses for each; out of respect for your time, we have tried to make our responses brief. Again, we thank you for your effort and insightful comments.

Response 1: Thank you for your suggestion. We have created two separate sections “Results” and “Discussion” in response to your strong recommendation. We hope that the Discussion section is clearer and better explains our interpretations of what the results mean in terms of small-shovel extraction activity in South Korea.

Response 2: We hope that this is now better clarified throughout the manuscript. Our formal definition of extraction distance is given on lines 97-99:

“We defined extraction distance for small-shovel operations as the distance the extractor travels, starting when the small-shovel leaves the forest road or landing area and ending when it returns to the landing.”

Response 3: Thank you for this comment. We did not mean to imply that log extraction productivity increases with extraction distance. (Although, yes, that is want our results counterintuitively seem to imply.) Rather, we meant to say that the reason for this seemingly illogical result has to do with the specific terrain of South Korea (highly sloped) and the gravity method used in harvesting, which moves the logs significant distances without any mechanical aid. That is, the distance the logs travel from the felling area to the landing area (where they are picked up by the extractor) is significant, which increases efficiency.

We have changed this paragraph (lines 163-173). Please let us know if you feel our reasoning is incorrect or unclear.

“Another important variable that influences SS productivity was the extraction distance. Both the Ghaffariyan et al. [39] and Strandgard et al. [40] studies found that productivity was significantly related to extraction distance since the load travel time accounted for over one quarter of the variation in cycle time. In addition, extraction productivity increased with a decrease in extraction distance [41-43]. However, this study implied that an increased extraction distance would be positively and significantly correlated with SS productivity (p< 0.001; r=0.8262; Fig. 7). The operation of SS in South Korea, unlike the ground-based extraction method, uses gravity. During the operation, the throwing and rolling activity, which is done to transfer logs from the felling area down to the landing area, may be associated with a large number of logs and long distances, whereas the load travel time was not affected. Thus, the productivity of SS depends on the number of logs per extraction cycle and extraction distance.”

Response 4: Thank you for your comments. We believe some of this is resolved in the paragraph cited above. We also think that lines 192-197 address this to some extent as well.

“The SS productivity model showed that productivity improved as tree volume and distance increased; the average tree volume ranged from 0.15 to 0.50 m3, and the mean extraction distance was between 40 and 70 m (Fig. 9). The data indicated that, when the volume of trees extracted increased from 0.15 m3 to 0.50 m3 (and the extraction distance ranged between 40 and 70 m), productivity increased by up to 30%. This result may be explained by the fact that efficiency improved with larger tree volumes and an increased number of logs at the stump area.”

Please also see Fig. 9.

Response 5: Thank you for your comment. You make an excellent point. We did not mean for those examples to be used to compare productivity. Our purpose in citing these studies was to help explain overall trends. In addition, small-shovel extraction method was not shovel logging patterns: tree length and whole tree (Session and Boston, 2013). Further, we were unable to find studies that look at this type of terrain using our approach.

Response 6: Thank you for your comment. While we continue to think that extraction distance is a strong variable. We have made the following adjustments/additions:

Response 7: We have changed the figure captions to reflect this comment. We hope this addresses your concern.

Point 8: The manuscript needs less descriptions about correlation between stand density, Dbh, and average stem volume. Fig 6 has no value in this manuscript, and should be removed.

Response 8: We have removed these from the paper.

Point 9: The manuscript needs more methods descriptions = definitions of work tasks, system descriptions, machine descriptions, etc.

o What typical manufacturer of excavators, typical boom lengths, grapple types?, Please provide a figure of how the excavator works.

Response : We found that many excavators used in manufacturing and SS operations are similar, only the head is changed. Therefore, we have added a description of boom length and grapple type to Fig. 1 to help. This photo also shows the excavator at work.

o How many logs does the boom reach per stationary point?

Response : Unfortunately, due to the nature of the data, we cannot say precisely how many logs the boom can reach from a stationary point. However, we can say that the SSs covered a distance of 30 m.

o Which is the excavator’s travel direction in terms of the slope direction?

Response : We have added some further description of the harvesting procedure on lines 105-107. We hope this clarifies the process a bit.

Response : The average road density in the study units is 108 m/ha (ranged from 32 to 188 m/ha). However, this is in the rural study areas, not Korea overall. We also addressed in line 96-97.

o Line 134: Hauling distance = what distance is that? Tractors? Trucks?

Response : We have the this to changed extraction distance on line 96.

o All of the above is essential information if international readers are to understand your results.

Response : Thank you for your comment. We hope our changes help readers understand our study and results better.

Point 10: There are many other errors that need to be fixed: SI units only in Table 2, Fig 10, language in the conclusions, Patents? (there are none), etc. Please have your co-authors and colleagues critically review your revised manuscript before sending it in again

Response 10: Thank you for noting these issues. We have colleagues and co-authors carefully review the manuscript and make revisions. We have corrected theses errors, and we hope that the overall clarity and readability of the text has improved.

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

The authors have made some changes in the manuscript but not as much as they imply in their cover letter.

Where are the two seperate sections? "We have created two separate sections “Results” and “Discussion” in response to your strong recommendation. " Just do this!

The main problem with the manuscript is regarding extraction distance,. The authors are mixing different definitions of extraction distance, which is most likely why their results regarding Extraction Distance are so strange.

All of their references regarding Extraction Distance define Extraction Distance in one-way terms (ie. only from stump to landing), while the authors here choose two-way (there and back) distance. See eg. Manner 2015 , https://pub.epsilon.slu.se/12821/ section 1.3.2 for correct distance terminology.

The authors should rather term their distance "Total Travelled Distance" or "Total Driven Distance". See eg. Berg et al. 2019, https://doi.org/10.17221/23/2019-JFS .Then they can discuss their findings in relation to other references' Total Travelled Distance. Because as the manuscript is now written, the manuscript compares "apples and oranges" (one- vs two-way distances). Change your wording throughout the manuscript please!

Also, I have previously asked the authors to describe how their "extraction distance" (in reality, Total Driven Distance) was determined. (Lines 96-97) and they have yet to do so. Please stop wasting our time and provide this!

Line 166: change increased to increases = "... extraction productivity increases with a decrease in..."

Moreover, the authors propose that SS is not a ground-based extraction method. However, SS is still ground based, see eg. page 5-6 of: https://www.competenz.org.nz/assets/Uploads/Ground-based-Logging-2018.pdf , or https://jingxinwang.forestry.wvu.edu/files/d/b95faf5d-3e87-41c8-84da-d443a9d8ce71/gextract.pdf, or any reputable Forest Operations book. Please change your categorization in the manuscript.

Response to point 5: Please compare your results with previous studies of excavators working as shovel loggers/hoe chuckers (there are previously published studies available). References regarding excavators are more relevant than references regarding forwarders. Refer to eg. Session and Boston, 2013 and other studies comapring hoe chucking, shovel logging. This must be done!

Figure 1 caption: jaw instead of jar!

Figure 3: which previous studies? See eg. Berg et al. 2019, FIg. 3 how to define previous studies in the figure caption.

Figure 7: x-axis= Average Total Driven Distance

Table 1: column heading = Average Total Driven Distance; also, Define DBH (all abreviations should be defined in the caption).

Table 2: column heading = small shovel

Keyword "excavator with a log grapple" is not a good keyword. "shovel logging" is better.

Gahffarian is spellt wrong in the ref. list..

Author Response

The authors have made some changes in the manuscript but not as much as they imply in their cover letter.

Point 1. Where are the two separate sections? "We have created two separate sections “Results” and “Discussion” in response to your strong recommendation. " Just do this!

Thank you for your suggestion. We have created two separate sections “Results” and “Discussion” in response to your strong recommendation.

Point 2. The main problem with the manuscript is regarding extraction distance,. The authors are mixing different definitions of extraction distance, which is most likely why their results regarding Extraction Distance are so strange.

Thank you for this comment. We changed extraction distance to Travel driven distance (TDD) in this paper.

Point 3. All of their references regarding Extraction Distance define Extraction Distance in one-way terms (ie. only from stump to landing), while the authors here choose two-way (there and back) distance. See eg. Manner 2015 , https://pub.epsilon.slu.se/12821/ section 1.3.2 for correct distance terminology.

Thank you for this reference. We changed extraction distance to Travel driven distance (TDD) in this paper.

Point 4. The authors should rather term their distance "Total Travelled Distance" or "Total Driven Distance". See eg. Berg et al. 2019, https://doi.org/10.17221/23/2019-JFS. Then they can discuss their findings in relation to other references' Total Travelled Distance. Because as the manuscript is now written, the manuscript compares "apples and oranges" (one- vs two-way distances). Change your wording throughout the manuscript please!

Thank you for this reference. We changed extraction distance to Travel driven distance (TDD) in this paper.

Point 5. Also, I have previously asked the authors to describe how their "extraction distance" (in reality, Total Driven Distance) was determined. (Lines 96-97) and they have yet to do so. Please stop wasting our time and provide this!

Thank you for this reference. We changed extraction distance to Travel driven distance (TDD) in this paper.

Point 6. Line 166: change increased to increases = "... extraction productivity increases with a decrease in..."

We changed it in line 257.

Point 7. Moreover, the authors propose that SS is not a ground-based extraction method. However, SS is still ground based, see eg. page 5-6 of: https://www.competenz.org.nz/assets/Uploads/Ground-based-Logging-2018.pdf , or https://jingxinwang.forestry.wvu.edu/files/d/b95faf5d-3e87-41c8-84da-d443a9d8ce71/gextract.pdf, or any reputable Forest Operations book. Please change your categorization in the manuscript.

We changed it to excavator extraction method in line 266-267.

“The operation of SS in South Korea, unlike the excavator extraction method (a.k.a., shovel logging), uses gravity.”

Point 8. Response to point 5: Please compare your results with previous studies of excavators working as shovel loggers/hoe chuckers (there are previously published studies available). References regarding excavators are more relevant than references regarding forwarders. Refer to eg. Session and Boston, 2013 and other studies comapring hoe chucking, shovel logging. This must be done!

We added Session and Boston, 2013 reference in line 245.

“Shovel logging productivity is affected by the number of swings and road spacing [36].”

Point 9. Figure 1 caption: jaw instead of jar!

We changed it in Figure 1.

Point 10. Figure 3: which previous studies? See eg. Berg et al. 2019, FIg. 3 how to define previous studies in the figure caption.

Thank you for your suggestion. We added more information about previous studies in Fig 3.

Point 11. Figure 7: x-axis= Average Total Driven Distance

We changed “extraction distance” to “average total driven distance” in Fig 7.

Point 12. Table 1: column heading = Average Total Driven Distance; also, Define DBH (all abreviations should be defined in the caption).

We do change the “extraction distance” to “average total driven distance”. We define the DBH in Table 1.

Point 13. Table 2: column heading = small shovel

We changed it in Table 2.

Point 14. Keyword "excavator with a log grapple" is not a good keyword. "shovel logging" is better.

We changed it in Keyword.

Point 15. Gahffarian is spellt wrong in the ref. list..

We changed Ghaffariyan Ref. 53.

Author Response File: Author Response.docx